diff --git a/assets/js/components/email-reporting/FrequencySelector.js b/assets/js/components/email-reporting/FrequencySelector.js
index f78c398c8bf..a6753cfa831 100644
--- a/assets/js/components/email-reporting/FrequencySelector.js
+++ b/assets/js/components/email-reporting/FrequencySelector.js
@@ -99,7 +99,7 @@ export default function FrequencySelector( { isUserSubscribed, isLoading } ) {
 		},
 		monthly: {
 			label: __( 'Monthly', 'google-site-kit' ),
-			period: __( 'Last 28 days', 'google-site-kit' ),
+			period: __( 'Last month', 'google-site-kit' ),
 			description: __(
 				'Sent on the 1st of each month',
 				'google-site-kit'
diff --git a/assets/js/components/email-reporting/__snapshots__/FrequencySelector.test.js.snap b/assets/js/components/email-reporting/__snapshots__/FrequencySelector.test.js.snap
index c428e727987..4a86f5883ac 100644
--- a/assets/js/components/email-reporting/__snapshots__/FrequencySelector.test.js.snap
+++ b/assets/js/components/email-reporting/__snapshots__/FrequencySelector.test.js.snap
@@ -75,7 +75,7 @@ exports[`FrequencySelector Story states (visual + DOM) Monthly selected renders
           <span
             class="googlesitekit-typography googlesitekit-typography--body googlesitekit-typography--small"
           >
-            Last 28 days
+            Last month
           </span>
         </div>
         <div
@@ -210,7 +210,7 @@ exports[`FrequencySelector Story states (visual + DOM) Previously saved frequenc
           <span
             class="googlesitekit-typography googlesitekit-typography--body googlesitekit-typography--small"
           >
-            Last 28 days
+            Last month
           </span>
         </div>
         <div
@@ -345,7 +345,7 @@ exports[`FrequencySelector Story states (visual + DOM) Previously saved frequenc
           <span
             class="googlesitekit-typography googlesitekit-typography--body googlesitekit-typography--small"
           >
-            Last 28 days
+            Last month
           </span>
         </div>
         <div
@@ -480,7 +480,7 @@ exports[`FrequencySelector Story states (visual + DOM) Quarterly selected render
           <span
             class="googlesitekit-typography googlesitekit-typography--body googlesitekit-typography--small"
           >
-            Last 28 days
+            Last month
           </span>
         </div>
         <div
@@ -615,7 +615,7 @@ exports[`FrequencySelector Story states (visual + DOM) Weekly selected (default
           <span
             class="googlesitekit-typography googlesitekit-typography--body googlesitekit-typography--small"
           >
-            Last 28 days
+            Last month
           </span>
         </div>
         <div
@@ -750,7 +750,7 @@ exports[`FrequencySelector Story states (visual + DOM) Weekly selected with Sund
           <span
             class="googlesitekit-typography googlesitekit-typography--body googlesitekit-typography--small"
           >
-            Last 28 days
+            Last month
           </span>
         </div>
         <div
diff --git a/includes/Core/Email_Reporting/Initiator_Task.php b/includes/Core/Email_Reporting/Initiator_Task.php
index 3d4a68c2b27..12bf1e24aad 100644
--- a/includes/Core/Email_Reporting/Initiator_Task.php
+++ b/includes/Core/Email_Reporting/Initiator_Task.php
@@ -117,7 +117,7 @@ public static function build_reference_dates( $frequency, $timestamp ) {
 
 		$period_lengths = array(
 			Email_Reporting_Settings::FREQUENCY_WEEKLY    => 7,
-			Email_Reporting_Settings::FREQUENCY_MONTHLY   => 30,
+			Email_Reporting_Settings::FREQUENCY_MONTHLY   => (int) $send_date->format( 't' ),
 			Email_Reporting_Settings::FREQUENCY_QUARTERLY => 90,
 		);
 
diff --git a/tests/phpunit/integration/Core/Email_Reporting/Initiator_TaskTest.php b/tests/phpunit/integration/Core/Email_Reporting/Initiator_TaskTest.php
index 541ffc43c76..cf3fbbe476f 100644
--- a/tests/phpunit/integration/Core/Email_Reporting/Initiator_TaskTest.php
+++ b/tests/phpunit/integration/Core/Email_Reporting/Initiator_TaskTest.php
@@ -201,7 +201,7 @@ public function test_handle_callback_action_without_subscribers_still_schedules_
 	/**
 	 * @dataProvider data_build_reference_dates_uses_expected_period_length
 	 */
-	public function test_build_reference_dates_uses_expected_period_length( $frequency, $expected_days ) {
+	public function test_build_reference_dates_uses_expected_period_length( $frequency, $expected_days, $timestamp_string ) {
 		$original_timezone_string = get_option( 'timezone_string' );
 		$original_gmt_offset      = get_option( 'gmt_offset' );
 
@@ -209,7 +209,7 @@ public function test_build_reference_dates_uses_expected_period_length( $frequen
 		update_option( 'gmt_offset', 0 );
 
 		try {
-			$timestamp = strtotime( '2026-03-16 00:00:00 UTC' );
+			$timestamp = strtotime( $timestamp_string );
 
 			$reference_dates = Initiator_Task::build_reference_dates(
 				$frequency,
@@ -256,9 +256,12 @@ public function test_build_reference_dates_uses_previous_day_as_send_date() {
 
 	public function data_build_reference_dates_uses_expected_period_length() {
 		return array(
-			'weekly'    => array( Email_Reporting_Settings::FREQUENCY_WEEKLY, 7 ),
-			'monthly'   => array( Email_Reporting_Settings::FREQUENCY_MONTHLY, 30 ),
-			'quarterly' => array( Email_Reporting_Settings::FREQUENCY_QUARTERLY, 90 ),
+			'weekly'               => array( Email_Reporting_Settings::FREQUENCY_WEEKLY, 7, '2026-03-16 00:00:00 UTC' ),
+			'monthly_31_day_month' => array( Email_Reporting_Settings::FREQUENCY_MONTHLY, 31, '2026-04-01 00:00:00 UTC' ),
+			'monthly_30_day_month' => array( Email_Reporting_Settings::FREQUENCY_MONTHLY, 30, '2026-07-01 00:00:00 UTC' ),
+			'monthly_28_day_month' => array( Email_Reporting_Settings::FREQUENCY_MONTHLY, 28, '2026-03-01 00:00:00 UTC' ),
+			'monthly_29_day_leap'  => array( Email_Reporting_Settings::FREQUENCY_MONTHLY, 29, '2028-03-01 00:00:00 UTC' ),
+			'quarterly'            => array( Email_Reporting_Settings::FREQUENCY_QUARTERLY, 90, '2026-03-16 00:00:00 UTC' ),
 		);
 	}
 }