diff --git a/.env.example b/.env.example
index af492e576..20415d125 100644
--- a/.env.example
+++ b/.env.example
@@ -288,3 +288,6 @@ PAYMENTS_SERVICE_OAUTH2_SCOPES=payment-profile/read
 L5_SWAGGER_OPEN_API_SPEC_VERSION=3.1.0
 
 SCHEDULER_OUTPUT_TO_STDOUT=false
+
+# registration stats response cache lifetime in seconds (0 disables the cache)
+CACHE_API_RESPONSE_REGISTRATION_STATS_LIFETIME=600
diff --git a/app/ModelSerializers/Summit/SummitRegistrationStatsSerializer.php b/app/ModelSerializers/Summit/SummitRegistrationStatsSerializer.php
index 7f148b63b..2e6bb1e58 100644
--- a/app/ModelSerializers/Summit/SummitRegistrationStatsSerializer.php
+++ b/app/ModelSerializers/Summit/SummitRegistrationStatsSerializer.php
@@ -13,6 +13,8 @@
  **/
 use App\Http\Exceptions\HTTP403ForbiddenException;
 use App\Utils\FilterUtils;
+use Illuminate\Support\Facades\Cache;
+use Illuminate\Support\Facades\Config;
 use Illuminate\Support\Facades\Log;
 use libs\utils\JsonUtils;
 use models\summit\Summit;
@@ -36,6 +38,45 @@ public function serialize($expand = null, array $fields = [], array $relations =
     {
         $summit = $this->object;
         if (!$summit instanceof Summit) return [];
+
+        $ttl = intval(Config::get('cache_api_response.registration_stats_response_lifetime', 600));
+        // the endpoints are admin only, so the key does not depend on the caller
+        if ($ttl <= 0)
+            return $this->buildValues($summit, $expand, $fields, $relations, $params);
+
+        $filter = $params['filter'] ?? null;
+        $start_date = null;
+        $end_date = null;
+        if ($filter instanceof Filter) list($start_date, $end_date) = FilterUtils::parseDateRangeUTC($filter);
+
+        $key = sprintf
+        (
+            'registration_stats_%s_%s_%s_%s',
+            $summit->getId(),
+            $start_date?->getTimestamp() ?? 'null',
+            $end_date?->getTimestamp() ?? 'null',
+            md5(json_encode([$expand, $fields, $relations]))
+        );
+
+        $values = Cache::get($key);
+        if (!is_array($values)) {
+            $values = $this->buildValues($summit, $expand, $fields, $relations, $params);
+            Cache::put($key, $values, $ttl);
+        }
+        return $values;
+    }
+
+    /**
+     * @param Summit $summit
+     * @param null $expand
+     * @param array $fields
+     * @param array $relations
+     * @param array $params
+     * @return array
+     * @throws \Exception
+     */
+    private function buildValues(Summit $summit, $expand, array $fields, array $relations, array $params): array
+    {
         $values = parent::serialize($expand, $fields, $relations, $params);
 
         $filter = $params['filter'] ?? null;
diff --git a/app/Models/Foundation/Summit/SummitRegistrationStats.php b/app/Models/Foundation/Summit/SummitRegistrationStats.php
index 37aad51aa..e0d423567 100644
--- a/app/Models/Foundation/Summit/SummitRegistrationStats.php
+++ b/app/Models/Foundation/Summit/SummitRegistrationStats.php
@@ -50,6 +50,12 @@ private static function getDefaultTimeZoneOffset(?DateTime $now = null){
         return $defaultSSTimeZone->getOffset($now) / 3600;
     }
 
+    /**
+     * Known limitation: a single fixed offset is used for the whole summit, the one in effect on its begin date.
+     * Tickets bought under a different offset (i.e. across a DST change) can fall in the neighbouring
+     * hour/day bucket of the purchased tickets histogram. Kept as is on purpose, see ClickUp task 86bcjg0u6.
+     * @return float|int
+     */
     private function getTimeZoneOffset(){
         try {
             $tz = $this->getTimeZone();
@@ -105,8 +111,7 @@ public function getActiveTicketsCount(?DateTime $startDate  = null, ?DateTime $e
         try {
             $sql = <<<SQL
           select COUNT(SummitAttendeeTicket.ID) FROM SummitAttendeeTicket
-INNER JOIN SummitOrder ON SummitOrder.ID = SummitAttendeeTicket.OrderID
-WHERE SummitOrder.SummitID = :summit_id AND 
+WHERE SummitAttendeeTicket.SummitID = :summit_id AND 
       SummitAttendeeTicket.IsActive = 1 AND 
       SummitAttendeeTicket.Status = 'Paid'
 SQL;
@@ -134,8 +139,7 @@ public function getInactiveTicketsCount(?DateTime $startDate  = null, ?DateTime
         try {
             $sql = <<<SQL
           select COUNT(SummitAttendeeTicket.ID) FROM SummitAttendeeTicket
-INNER JOIN SummitOrder ON SummitOrder.ID = SummitAttendeeTicket.OrderID
-WHERE SummitOrder.SummitID = :summit_id AND 
+WHERE SummitAttendeeTicket.SummitID = :summit_id AND 
       SummitAttendeeTicket.IsActive = 0 AND 
       SummitAttendeeTicket.Status = 'Paid'
 SQL;
@@ -163,9 +167,8 @@ public function getActiveAssignedTicketsCount(?DateTime $startDate  = null, ?Dat
         try {
             $sql = <<<SQL
 SELECT COUNT(SummitAttendeeTicket.ID) FROM SummitAttendeeTicket
-INNER JOIN SummitOrder ON SummitOrder.ID = SummitAttendeeTicket.OrderID
 INNER JOIN SummitAttendee ON SummitAttendee.ID = SummitAttendeeTicket.OwnerID
-WHERE SummitOrder.SummitID = :summit_id AND 
+WHERE SummitAttendeeTicket.SummitID = :summit_id AND 
       SummitAttendeeTicket.IsActive = 1 AND 
       SummitAttendeeTicket.Status = 'Paid'
 SQL;
@@ -220,8 +223,7 @@ public function getTotalPaymentAmountCollected(?DateTime $startDate  = null, ?Da
         try {
             $sql = <<<SQL
 SELECT SUM(SummitAttendeeTicket.RawCost - SummitAttendeeTicket.Discount)  FROM SummitAttendeeTicket
-INNER JOIN SummitOrder ON SummitOrder.ID = SummitAttendeeTicket.OrderID
-WHERE SummitOrder.SummitID = :summit_id AND 
+WHERE SummitAttendeeTicket.SummitID = :summit_id AND 
       SummitAttendeeTicket.Status = 'Paid'
 SQL;
 
@@ -252,10 +254,9 @@ public function getTotalRefundAmountEmitted(?DateTime $startDate  = null, ?DateT
       SELECT SUM(SummitRefundRequest.RefundedAmount) FROM `SummitRefundRequest`
 INNER JOIN SummitAttendeeTicketRefundRequest on SummitAttendeeTicketRefundRequest.ID = SummitRefundRequest.ID
 INNER JOIN SummitAttendeeTicket on SummitAttendeeTicket.ID = SummitAttendeeTicketRefundRequest.TicketID
-INNER JOIN SummitOrder on SummitOrder.ID = SummitAttendeeTicket.OrderID
 WHERE
       SummitRefundRequest.Status='Approved' AND 
-      SummitOrder.SummitID = :summit_id
+      SummitAttendeeTicket.SummitID = :summit_id
 SQL;
             $sql = self::addDatesFilteringWithTimeZone($sql, "SummitRefundRequest", "Created", $startDate, $endDate);
 
@@ -280,9 +281,8 @@ public function getActiveTicketsCountPerTicketType(?DateTime $startDate  = null,
         try {
             $sql = <<<SQL
 select SummitTicketType.Name AS type, COUNT(SummitAttendeeTicket.ID) as qty FROM SummitAttendeeTicket
-INNER JOIN SummitOrder ON SummitOrder.ID = SummitAttendeeTicket.OrderID
 INNER JOIN SummitTicketType ON SummitAttendeeTicket.TicketTypeID = SummitTicketType.ID
-WHERE SummitOrder.SummitID = :summit_id AND 
+WHERE SummitAttendeeTicket.SummitID = :summit_id AND 
       SummitAttendeeTicket.IsActive = 1 AND 
       SummitAttendeeTicket.Status = 'Paid'
 SQL;
@@ -309,7 +309,6 @@ public function getCheckedInActiveTicketsCountPerTicketType(?DateTime $startDate
         try {
             $sql = <<<SQL
 SELECT SummitTicketType.Name AS type, COUNT(SummitAttendeeTicket.ID) as qty FROM SummitAttendeeTicket
-INNER JOIN SummitOrder ON SummitOrder.ID = SummitAttendeeTicket.OrderID
 INNER JOIN SummitTicketType ON SummitAttendeeTicket.TicketTypeID = SummitTicketType.ID
 INNER JOIN SummitAttendee ON SummitAttendee.ID = SummitAttendeeTicket.OwnerID
 INNER JOIN SummitAttendeeBadge ON SummitAttendeeBadge.TicketID = SummitAttendeeTicket.ID
@@ -317,7 +316,7 @@ public function getCheckedInActiveTicketsCountPerTicketType(?DateTime $startDate
 INNER JOIN SummitBadgeType_AccessLevels ON SummitBadgeType_AccessLevels.SummitBadgeTypeID = SummitBadgeType.ID
 INNER JOIN SummitAccessLevelType ON SummitAccessLevelType.ID = SummitBadgeType_AccessLevels.SummitAccessLevelTypeID
 WHERE
-      SummitOrder.SummitID = :summit_id AND
+      SummitAttendeeTicket.SummitID = :summit_id AND
       SummitAttendeeTicket.IsActive = 1 AND
       SummitAttendeeTicket.Status = 'Paid' AND
       SummitAttendee.SummitHallCheckedIn = 1 AND
@@ -348,9 +347,8 @@ public function getActiveBadgesCountPerBadgeType(?DateTime $startDate  = null, ?
 SELECT SummitBadgeType.Name as type, COUNT(DISTINCT(SummitAttendeeBadge.ID)) as qty FROM SummitAttendeeBadge
 INNER JOIN SummitBadgeType ON SummitAttendeeBadge.BadgeTypeID = SummitBadgeType.ID
 INNER JOIN SummitAttendeeTicket ON SummitAttendeeTicket.ID = SummitAttendeeBadge.TicketID
-INNER JOIN SummitOrder ON SummitOrder.ID = SummitAttendeeTicket.OrderID
 INNER JOIN SummitTicketType ON SummitAttendeeTicket.TicketTypeID = SummitTicketType.ID
-WHERE SummitOrder.SummitID = :summit_id AND 
+WHERE SummitAttendeeTicket.SummitID = :summit_id AND 
       SummitAttendeeTicket.IsActive = 1 AND 
       SummitAttendeeTicket.Status = 'Paid'
 SQL;
@@ -379,12 +377,11 @@ public function getActiveCheckedInBadgesCountPerBadgeType(?DateTime $startDate
 SELECT SummitBadgeType.Name as type, COUNT(DISTINCT(SummitAttendeeBadge.ID)) as qty FROM SummitAttendeeBadge
 INNER JOIN SummitBadgeType ON SummitAttendeeBadge.BadgeTypeID = SummitBadgeType.ID
 INNER JOIN SummitAttendeeTicket ON SummitAttendeeTicket.ID = SummitAttendeeBadge.TicketID
-INNER JOIN SummitOrder ON SummitOrder.ID = SummitAttendeeTicket.OrderID
 INNER JOIN SummitTicketType ON SummitAttendeeTicket.TicketTypeID = SummitTicketType.ID
 INNER JOIN SummitAttendee ON SummitAttendee.ID = SummitAttendeeTicket.OwnerID
 INNER JOIN SummitBadgeType_AccessLevels ON SummitBadgeType_AccessLevels.SummitBadgeTypeID = SummitBadgeType.ID
 INNER JOIN SummitAccessLevelType ON SummitAccessLevelType.ID = SummitBadgeType_AccessLevels.SummitAccessLevelTypeID
-WHERE SummitOrder.SummitID = :summit_id AND
+WHERE SummitAttendeeTicket.SummitID = :summit_id AND
       SummitAttendeeTicket.IsActive = 1 AND
       SummitAttendeeTicket.Status = 'Paid' AND
       SummitAttendee.SummitHallCheckedIn = 1 AND
@@ -608,7 +605,6 @@ public function getActiveTicketsPerBadgeFeatureType(?DateTime $startDate  = null
         try {
             $sql = <<<SQL
 SELECT  SummitBadgeFeatureType.Name as type, COUNT(DISTINCT(SummitAttendeeTicket.ID)) as qty FROM SummitAttendeeTicket
-INNER JOIN SummitOrder ON SummitOrder.ID = SummitAttendeeTicket.OrderID
 INNER JOIN SummitAttendeeBadge ON SummitAttendeeBadge.TicketID = SummitAttendeeTicket.ID
 INNER JOIN SummitBadgeType ON SummitBadgeType.ID = SummitAttendeeBadge.BadgeTypeID
 LEFT JOIN SummitBadgeType_BadgeFeatures ON SummitBadgeType_BadgeFeatures.SummitBadgeTypeID = SummitBadgeType.ID
@@ -618,7 +614,7 @@ public function getActiveTicketsPerBadgeFeatureType(?DateTime $startDate  = null
 WHERE
 SummitAttendeeTicket.IsActive = 1 AND
 SummitAttendeeTicket.Status = 'Paid' AND
-SummitOrder.SummitID = :summit_id
+SummitAttendeeTicket.SummitID = :summit_id
 SQL;
 
             $sql = self::addDatesFilteringWithTimeZone($sql, "SummitAttendeeTicket", "Created", $startDate, $endDate);
@@ -644,7 +640,6 @@ public function getAttendeesCheckinPerBadgeFeatureType(?DateTime $startDate  = n
         try {
             $sql = <<<SQL
 SELECT  SummitBadgeFeatureType.Name as type, COUNT(DISTINCT(SummitAttendeeTicket.ID)) as qty FROM SummitAttendeeTicket
-INNER JOIN SummitOrder ON SummitOrder.ID = SummitAttendeeTicket.OrderID
 INNER JOIN SummitAttendeeBadge ON SummitAttendeeBadge.TicketID = SummitAttendeeTicket.ID
 INNER JOIN SummitBadgeType ON SummitBadgeType.ID = SummitAttendeeBadge.BadgeTypeID
 LEFT JOIN SummitBadgeType_BadgeFeatures ON SummitBadgeType_BadgeFeatures.SummitBadgeTypeID = SummitBadgeType.ID
@@ -655,7 +650,7 @@ public function getAttendeesCheckinPerBadgeFeatureType(?DateTime $startDate  = n
 WHERE
 SummitAttendeeTicket.IsActive = 1 AND
 SummitAttendeeTicket.Status = 'Paid' AND
-SummitOrder.SummitID = :summit_id AND
+SummitAttendeeTicket.SummitID = :summit_id AND
 SummitAttendee.SummitHallCheckedIn = 1
 SQL;
 
@@ -806,9 +801,8 @@ public function getPurchasedTicketsGroupedBy
 SELECT COUNT(SummitAttendeeTicket.ID) as qty, 
        DATE_FORMAT(CONVERT_TZ(SummitAttendeeTicket.TicketBoughtDate,'+00:00','{$offset}'), '{$date_format}') AS label 
 FROM SummitAttendeeTicket
-INNER JOIN SummitOrder ON SummitOrder.ID = SummitAttendeeTicket.OrderID
 WHERE
-SummitOrder.SummitID = :summit_id AND
+SummitAttendeeTicket.SummitID = :summit_id AND
 SummitAttendeeTicket.IsActive = 1 AND 
 SummitAttendeeTicket.Status = 'Paid'
 SQL;
@@ -833,22 +827,15 @@ public function getPurchasedTicketsGroupedBy
             $sql .= " GROUP BY DATE_FORMAT(CONVERT_TZ(SummitAttendeeTicket.TicketBoughtDate,'+00:00','{$offset}'), '{$date_format}')";
             $sql .= " ORDER BY SummitAttendeeTicket.TicketBoughtDate ASC";
 
-            $count_sql = <<<SQL
-SELECT COUNT(*) FROM ({$sql}) T1
-SQL;
-            $stmt = $this->prepareRawSQL($count_sql, ['summit_id' => $this->id]);
-            $res = $stmt->executeQuery();
-            $res = $res->fetchFirstColumn();
-
-            $total = count($res) > 0 ? intval($res[0]) : 0;
-
-            $sql .= " LIMIT {$pagingInfo->getPerPage()} OFFSET {$pagingInfo->getOffset()} ";
             Log::debug(sprintf("Summit::getTicketsPurchasedGroupedBy sql %s", $sql));
 
+            // the histogram is computed once; the total is the number of buckets and the page is sliced here
             $stmt = $this->prepareRawSQL($sql, ['summit_id' => $this->id]);
             $res = $stmt->executeQuery();
-            $res = $res->fetchAllAssociative();
-            $res = count($res) > 0 ? $res : [];
+            $buckets = $res->fetchAllAssociative();
+
+            $total = count($buckets);
+            $res = array_slice($buckets, $pagingInfo->getOffset(), $pagingInfo->getPerPage());
 
             return new PagingResponse
             (
diff --git a/config/cache_api_response.php b/config/cache_api_response.php
index cb728400e..6ded09216 100644
--- a/config/cache_api_response.php
+++ b/config/cache_api_response.php
@@ -18,6 +18,7 @@
     'get_event_feedback_response_lifetime'  => env('CACHE_API_RESPONSE_GET_EVENT_FEEDBACK_LIFETIME', 600),
     'get_published_event_response_lifetime' => env('CACHE_API_RESPONSE_GET_PUBLISHED_EVENT_LIFETIME', 600),
     'get_summits_response_lifetime'         => env('CACHE_API_RESPONSE_GET_SUMMITS_LIFETIME', 600),
+    'registration_stats_response_lifetime'  => env('CACHE_API_RESPONSE_REGISTRATION_STATS_LIFETIME', 600),
     'file_url_lifetime'                     => env('CACHE_API_RESPONSE_FILE_URL_LIFETIME', 3600),
     'event_has_access_lifetime'             => env('CACHE_API_RESPONSE_EVENT_HAS_ACCESS_LIFETIME', 600),
 ];
\ No newline at end of file
diff --git a/database/migrations/model/Version20261021120000.php b/database/migrations/model/Version20261021120000.php
new file mode 100644
index 000000000..bc394817e
--- /dev/null
+++ b/database/migrations/model/Version20261021120000.php
@@ -0,0 +1,36 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Database\Migrations\Model;
+
+use Doctrine\DBAL\Schema\Schema;
+use Doctrine\Migrations\AbstractMigration;
+
+/**
+ * Backfills SummitAttendeeTicket.SummitID from the order for tickets that have an order but no summit,
+ * so the registration stats queries can filter on the ticket's own (indexed) SummitID.
+ */
+final class Version20261021120000 extends AbstractMigration
+{
+    public function getDescription(): string
+    {
+        return 'Back Fill Ticket table with summit id from orders (remaining rows)';
+    }
+
+    public function up(Schema $schema): void
+    {
+        $sql = <<<SQL
+UPDATE SummitAttendeeTicket t
+JOIN SummitOrder o ON o.ID = t.OrderID
+SET t.SummitID = o.SummitID
+WHERE t.SummitID IS NULL AND t.OrderID IS NOT NULL;
+SQL;
+
+        $this->addSql($sql);
+    }
+
+    public function down(Schema $schema): void
+    {
+    }
+}
diff --git a/tests/Repositories/RegistrationStatsCacheTest.php b/tests/Repositories/RegistrationStatsCacheTest.php
new file mode 100644
index 000000000..ba5cd1fa6
--- /dev/null
+++ b/tests/Repositories/RegistrationStatsCacheTest.php
@@ -0,0 +1,152 @@
+<?php namespace Tests\Repositories;
+/*
+ * Copyright 2026 OpenStack Foundation
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ **/
+
+use App\Http\Middleware\Doctrine\QueryTimingCollector;
+use App\Models\Foundation\Main\IGroup;
+use Illuminate\Support\Facades\Cache;
+use Illuminate\Support\Facades\Config;
+use ModelSerializers\SerializerRegistry;
+use Mockery;
+use Tests\InsertOrdersTestData;
+use Tests\InsertSummitTestData;
+use Tests\ProtectedApiTestCase;
+use utils\Filter;
+use utils\FilterParser;
+
+/**
+ * The registration stats response is cached per summit and date range. Tests observe how many
+ * queries a sequence of requests runs, never the cache key itself.
+ *
+ * @package Tests\Repositories
+ */
+final class RegistrationStatsCacheTest extends ProtectedApiTestCase
+{
+    use InsertSummitTestData;
+    use InsertOrdersTestData;
+
+    private const Lifetime = 'cache_api_response.registration_stats_response_lifetime';
+
+    /**
+     * @var array
+     */
+    private array $store = [];
+
+    /**
+     * @var int[] ttl of every Cache::put
+     */
+    private array $ttls = [];
+
+    protected function setUp(): void
+    {
+        $this->current_group = IGroup::TrackChairs;
+        parent::setUp();
+        self::insertSummitTestData();
+        self::InsertOrdersTestData();
+
+        $this->store = [];
+        $this->ttls = [];
+        // a stateful fake keeps the test off redis; clearing $store stands for the entry expiring
+        Cache::shouldReceive('put')->andReturnUsing(function ($key, $value, $ttl = null) {
+            $this->store[$key] = $value;
+            $this->ttls[] = $ttl;
+            return true;
+        });
+        Cache::shouldReceive('get')->andReturnUsing(function ($key, $default = null) {
+            return $this->store[$key] ?? $default;
+        });
+    }
+
+    protected function tearDown(): void
+    {
+        Mockery::close();
+        self::clearOrdersTestData();
+        self::clearSummitTestData();
+        parent::tearDown();
+    }
+
+    private function filter(?int $start = null, ?int $end = null): Filter
+    {
+        if (is_null($start)) return new Filter();
+        $expression = ["start_date>=$start"];
+        if (!is_null($end)) $expression[] = "end_date<=$end";
+        return FilterParser::parse($expression, ['start_date' => ['>='], 'end_date' => ['<=']]);
+    }
+
+    /**
+     * @return array [payload, number of queries the request ran]
+     */
+    private function request(?Filter $filter = null): array
+    {
+        $serializer = SerializerRegistry::getInstance()
+            ->getSerializer(self::$summit, SerializerRegistry::SerializerType_Admin_Registration_Stats);
+        QueryTimingCollector::reset();
+        $payload = $serializer->serialize(null, [], [], ['filter' => $filter ?? new Filter()]);
+        return [$payload, QueryTimingCollector::$count];
+    }
+
+    public function testSecondRequestInsideTheLifetimeDoesNotRunTheQueries(): void
+    {
+        Config::set(self::Lifetime, 600);
+
+        [$first, $first_queries] = $this->request();
+        [$second, $second_queries] = $this->request();
+
+        $this->assertGreaterThan(0, $first_queries, 'the first request must run the stats queries');
+        $this->assertSame(0, $second_queries);
+        $this->assertSame($first, $second);
+        $this->assertSame([600], $this->ttls);
+    }
+
+    public function testRequestAfterTheLifetimeRunsTheQueriesAgain(): void
+    {
+        Config::set(self::Lifetime, 600);
+
+        $this->request();
+        $this->store = []; // the entry expired
+
+        [, $queries] = $this->request();
+
+        $this->assertGreaterThan(0, $queries);
+        $this->assertCount(2, $this->ttls);
+    }
+
+    public function testZeroLifetimeDisablesTheCache(): void
+    {
+        Config::set(self::Lifetime, 0);
+
+        [, $first_queries] = $this->request();
+        [, $second_queries] = $this->request();
+
+        $this->assertGreaterThan(0, $first_queries);
+        $this->assertSame($first_queries, $second_queries);
+        $this->assertSame([], $this->ttls, 'nothing is stored when the cache is off');
+    }
+
+    public function testDifferentDateRangesDoNotShareAnEntry(): void
+    {
+        Config::set(self::Lifetime, 600);
+        $start = time() - 86400;
+
+        [, $unfiltered] = $this->request();
+        [, $filtered] = $this->request($this->filter($start, $start + 3600));
+        [, $filtered_again] = $this->request($this->filter($start, $start + 3600));
+        [, $other_range] = $this->request($this->filter($start, $start + 7200));
+
+        $this->assertGreaterThan(0, $unfiltered);
+        $this->assertGreaterThan(0, $filtered, 'a date range must not read the unfiltered entry');
+        $this->assertSame(0, $filtered_again);
+        $this->assertGreaterThan(0, $other_range);
+        $this->assertCount(3, $this->store);
+    }
+}
diff --git a/tests/Repositories/RegistrationStatsPayloadTest.php b/tests/Repositories/RegistrationStatsPayloadTest.php
new file mode 100644
index 000000000..12ea5de6a
--- /dev/null
+++ b/tests/Repositories/RegistrationStatsPayloadTest.php
@@ -0,0 +1,189 @@
+<?php namespace Tests\Repositories;
+/*
+ * Copyright 2026 OpenStack Foundation
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ **/
+
+use App\Models\Foundation\Main\IGroup;
+use App\Models\Foundation\Summit\IStatsConstants;
+use DateTime;
+use DateTimeZone;
+use Illuminate\Support\Facades\DB;
+use models\summit\Summit;
+use Tests\InsertOrdersTestData;
+use Tests\InsertSummitTestData;
+use Tests\ProtectedApiTestCase;
+use utils\PagingInfo;
+
+/**
+ * The registration stats queries filter on SummitAttendeeTicket.SummitID instead of joining
+ * SummitOrder. Each test computes the answer the old way (join on the order) and compares it with
+ * what the trait returns now, so the payload is proven unchanged rather than assumed.
+ *
+ * @package Tests\Repositories
+ */
+final class RegistrationStatsPayloadTest extends ProtectedApiTestCase
+{
+    use InsertSummitTestData;
+    use InsertOrdersTestData;
+
+    // the summit offset is taken at its begin date, so it is pinned to keep the buckets deterministic
+    // America/Chicago in July: UTC-05:00
+    private const SummitBeginDate = '2026-07-15 12:00:00';
+    private const LegacyOffset = '-05:00';
+
+    private Summit $stats_summit;
+
+    /**
+     * @var int[] ticket ids, one per seeded order
+     */
+    private array $ticket_ids = [];
+
+    protected function setUp(): void
+    {
+        $this->current_group = IGroup::TrackChairs;
+        parent::setUp();
+        self::insertSummitTestData();
+        self::InsertOrdersTestData();
+
+        self::$summit->setBeginDate(new DateTime(self::SummitBeginDate, new DateTimeZone('UTC')));
+        self::$em->flush();
+
+        foreach (self::$summit_orders as $order) {
+            $this->ticket_ids[] = $order->getTickets()->first()->getId();
+        }
+
+        // [0] inactive, [2] bought at 23:30 local on Jul 15, [3] bought 23:30 local on the day DST ends
+        DB::table('SummitAttendeeTicket')->where('ID', $this->ticket_ids[0])->update(['IsActive' => 0]);
+        DB::table('SummitAttendeeTicket')->whereIn('ID', array_slice($this->ticket_ids, 1))
+            ->update(['TicketBoughtDate' => '2026-07-20 15:00:00']);
+        DB::table('SummitAttendeeTicket')->where('ID', $this->ticket_ids[2])
+            ->update(['TicketBoughtDate' => '2026-07-16 04:30:00']);
+        DB::table('SummitAttendeeTicket')->where('ID', $this->ticket_ids[3])
+            ->update(['TicketBoughtDate' => '2026-11-02 05:30:00']);
+
+        $id = self::$summit->getId();
+        self::$em->clear();
+        $this->stats_summit = self::$em->find(Summit::class, $id);
+    }
+
+    protected function tearDown(): void
+    {
+        self::clearOrdersTestData();
+        self::clearSummitTestData();
+        parent::tearDown();
+    }
+
+    private function legacyScalar(string $sql): int
+    {
+        $rows = DB::connection('model')->select($sql, ['summit_id' => $this->stats_summit->getId()]);
+        return intval(array_values((array)$rows[0])[0]);
+    }
+
+    public function testTicketCountsMatchTheOrderJoin(): void
+    {
+        $join = 'FROM SummitAttendeeTicket t INNER JOIN SummitOrder o ON o.ID = t.OrderID WHERE o.SummitID = :summit_id';
+
+        $this->assertSame(9, $this->stats_summit->getActiveTicketsCount());
+        $this->assertSame(
+            $this->legacyScalar("SELECT COUNT(t.ID) $join AND t.IsActive = 1 AND t.Status = 'Paid'"),
+            $this->stats_summit->getActiveTicketsCount()
+        );
+        $this->assertSame(1, $this->stats_summit->getInactiveTicketsCount());
+        $this->assertSame(
+            $this->legacyScalar("SELECT COUNT(t.ID) $join AND t.IsActive = 0 AND t.Status = 'Paid'"),
+            $this->stats_summit->getInactiveTicketsCount()
+        );
+        $this->assertSame(
+            $this->legacyScalar(
+                "SELECT COUNT(t.ID) FROM SummitAttendeeTicket t INNER JOIN SummitOrder o ON o.ID = t.OrderID
+                 INNER JOIN SummitAttendee a ON a.ID = t.OwnerID
+                 WHERE o.SummitID = :summit_id AND t.IsActive = 1 AND t.Status = 'Paid'"
+            ),
+            $this->stats_summit->getActiveAssignedTicketsCount()
+        );
+    }
+
+    public function testTicketsPerTypeMatchTheOrderJoin(): void
+    {
+        $legacy = DB::connection('model')->select(
+            "SELECT tt.Name AS type, COUNT(t.ID) AS qty FROM SummitAttendeeTicket t
+             INNER JOIN SummitOrder o ON o.ID = t.OrderID
+             INNER JOIN SummitTicketType tt ON t.TicketTypeID = tt.ID
+             WHERE o.SummitID = :summit_id AND t.IsActive = 1 AND t.Status = 'Paid' GROUP BY tt.Name",
+            ['summit_id' => $this->stats_summit->getId()]
+        );
+        $legacy = array_map(fn($r) => ['type' => $r->type, 'qty' => intval($r->qty)], $legacy);
+        $current = array_map(
+            fn($r) => ['type' => $r['type'], 'qty' => intval($r['qty'])],
+            $this->stats_summit->getActiveTicketsCountPerTicketType()
+        );
+
+        $this->assertSame([['type' => 'TICKET TYPE 1', 'qty' => 9]], $current);
+        $this->assertSame($legacy, $current);
+    }
+
+    /**
+     * Same buckets as the query that joined SummitOrder, including the ticket bought at 23:30 local
+     * time (still Jul 15 although it is already Jul 16 in UTC).
+     */
+    public function testPurchasedTicketsHistogramMatchesTheOrderJoin(): void
+    {
+        $offset = self::LegacyOffset;
+        $legacy = DB::connection('model')->select(
+            "SELECT COUNT(t.ID) AS qty, DATE_FORMAT(CONVERT_TZ(t.TicketBoughtDate,'+00:00','{$offset}'), '%b %D') AS label
+             FROM SummitAttendeeTicket t INNER JOIN SummitOrder o ON o.ID = t.OrderID
+             WHERE o.SummitID = :summit_id AND t.IsActive = 1 AND t.Status = 'Paid'
+             GROUP BY DATE_FORMAT(CONVERT_TZ(t.TicketBoughtDate,'+00:00','{$offset}'), '%b %D')
+             ORDER BY t.TicketBoughtDate ASC",
+            ['summit_id' => $this->stats_summit->getId()]
+        );
+        $legacy = array_map(fn($r) => ['qty' => intval($r->qty), 'label' => $r->label], $legacy);
+
+        $response = $this->stats_summit->getPurchasedTicketsGroupedBy(IStatsConstants::GroupByDay, new PagingInfo(1, 100));
+        $current = array_map(
+            fn($r) => ['qty' => intval($r['qty']), 'label' => $r['label']],
+            $response->getItems()
+        );
+
+        $this->assertSame($legacy, $current);
+        $this->assertSame(count($legacy), $response->getTotal());
+        $this->assertSame('Jul 15th', $current[0]['label'], 'the 23:30 local purchase belongs to Jul 15');
+        $this->assertSame(1, $current[0]['qty']);
+    }
+
+    /**
+     * Pins the known limitation documented on getTimeZoneOffset(): one fixed offset for the whole
+     * summit. The ticket bought at 23:30 local time on Nov 1 (UTC-06:00 after DST ended) is bucketed
+     * with the July offset (UTC-05:00) and lands on Nov 2. Not a bug of this change; if the offset
+     * is ever fixed, this expectation changes with it.
+     */
+    public function testHistogramKeepsTheFixedSummitOffsetAcrossDst(): void
+    {
+        $response = $this->stats_summit->getPurchasedTicketsGroupedBy(IStatsConstants::GroupByDay, new PagingInfo(1, 100));
+        $labels = array_column($response->getItems(), 'label');
+
+        $this->assertContains('Nov 2nd', $labels);
+        $this->assertNotContains('Nov 1st', $labels);
+    }
+
+    public function testHistogramPaginatesTheBucketsInMemory(): void
+    {
+        $page1 = $this->stats_summit->getPurchasedTicketsGroupedBy(IStatsConstants::GroupByDay, new PagingInfo(1, 2));
+        $page2 = $this->stats_summit->getPurchasedTicketsGroupedBy(IStatsConstants::GroupByDay, new PagingInfo(2, 2));
+
+        $this->assertSame(3, $page1->getTotal());
+        $this->assertSame(3, $page2->getTotal());
+        $this->assertSame(['Jul 15th', 'Jul 20th'], array_column($page1->getItems(), 'label'));
+        $this->assertSame(['Nov 2nd'], array_column($page2->getItems(), 'label'));
+        $this->assertSame(2, $page1->getLastPage());
+    }
+}