diff --git a/Sources/Actions/Admin/Subscriptions.php b/Sources/Actions/Admin/Subscriptions.php
index 6805965ea4..bf378721d8 100644
--- a/Sources/Actions/Admin/Subscriptions.php
+++ b/Sources/Actions/Admin/Subscriptions.php
@@ -846,6 +846,7 @@ public function modifyUser(): void
 		// Setup the template.
 		Utils::$context['sub_template'] = 'modify_user_subscription';
 		Utils::$context['page_title'] = Lang::$txt[Utils::$context['action_type'] . '_subscriber'];
+		Theme::loadJavaScriptFile('paidsubs.js', ['defer' => true, 'minimize' => true], 'smf_paidsubs');
 
 		// If we haven't been passed the subscription ID get it.
 		if (Utils::$context['log_id'] && !Utils::$context['sub_id']) {
diff --git a/Themes/default/Admin.template.php b/Themes/default/Admin.template.php
index 7ccda036d9..c6f1c6f75d 100644
--- a/Themes/default/Admin.template.php
+++ b/Themes/default/Admin.template.php
@@ -725,7 +725,7 @@ function template_not_done()
 							<form action="', Config::$scripturl, Utils::$context['continue_get_data'], '" method="post" accept-charset="', Utils::$context['character_set'], '" name="autoSubmit" id="autoSubmit">';
 
 	// Do we have a token?
-	if (isset(Utils::$context['not_done_token']) && isset(Utils::$context[Utils::$context['not_done_token'] . '_token'], Utils::$context[Utils::$context['not_done_token'] . '_token_var']))
+	if (isset(Utils::$context['not_done_token'], Utils::$context[Utils::$context['not_done_token'] . '_token'], Utils::$context[Utils::$context['not_done_token'] . '_token_var']))
 		echo '
 							<input type="hidden" name="', Utils::$context[Utils::$context['not_done_token'] . '_token_var'], '" value="', Utils::$context[Utils::$context['not_done_token'] . '_token'], '">';
 
@@ -735,21 +735,7 @@ function template_not_done()
 							</form>
 						</div><!-- .windowbg -->
 					<script>
-						var countdown = ', Utils::$context['continue_countdown'], ';
-						doAutoSubmit();
-
-						function doAutoSubmit()
-						{
-							if (countdown == 0)
-								document.forms.autoSubmit.submit();
-							else if (countdown == -1)
-								return;
-
-							document.forms.autoSubmit.cont.value = "', Lang::$txt['not_done_continue'], ' (" + countdown + ")";
-							countdown--;
-
-							setTimeout(doAutoSubmit, 1000);
-						}
+						doAutoSubmit(', Utils::$context['continue_countdown'], ', ', Lang::$txt['not_done_continue'], ');
 					</script>';
 }
 
@@ -1526,21 +1512,7 @@ function template_repair_boards()
 	{
 		echo '
 					<script>
-						var countdown = 5;
-						doAutoSubmit();
-
-						function doAutoSubmit()
-						{
-							if (countdown == 0)
-								document.forms.recount_form.submit();
-							else if (countdown == -1)
-								return;
-
-							document.forms.recount_form.recount_now.value = "', Lang::$txt['errors_recount_now'], ' (" + countdown + ")";
-							countdown--;
-
-							setTimeout(doAutoSubmit, 1000);
-						}
+						doAutoSubmit(5, ', Utils::escapeJavaScript(Lang::$txt['errors_recount_now']), ', "recount_form", "recount_now");
 					</script>';
 	}
 }
diff --git a/Themes/default/ManageNews.template.php b/Themes/default/ManageNews.template.php
index 36661ec935..660af358f9 100644
--- a/Themes/default/ManageNews.template.php
+++ b/Themes/default/ManageNews.template.php
@@ -384,7 +384,7 @@ function template_email_members_send()
 					<div class="bar" style="width: ', Utils::$context['percentage_done'], '%;"></div>
 				</div>
 				<hr>
-				<input type="submit" name="b" value="', Lang::$txt['email_continue'], '" class="button">
+				<input type="submit" name="cont" value="', Lang::$txt['email_continue'], '" class="button">
 				<input type="hidden" name="', Utils::$context['session_var'], '" value="', Utils::$context['session_id'], '">
 				<input type="hidden" name="subject" value="', Utils::$context['subject'], '">
 				<input type="hidden" name="message" value="', Utils::$context['message'], '">
@@ -404,23 +404,9 @@ function template_email_members_send()
 			</div><!-- .windowbg -->
 		</form>
 
-	<script>
-		var countdown = 2;
-		doAutoSubmit();
-
-		function doAutoSubmit()
-		{
-			if (countdown == 0)
-				document.forms.autoSubmit.submit();
-			else if (countdown == -1)
-				return;
-
-			document.forms.autoSubmit.b.value = "', Lang::$txt['email_continue'], ' (" + countdown + ")";
-			countdown--;
-
-			setTimeout("doAutoSubmit();", 1000);
-		}
-	</script>';
+		<script>
+			doAutoSubmit(2, ', Utils::escapeJavaScript(Lang::$txt['email_continue']), ');
+		</script>';
 }
 
 /**
diff --git a/Themes/default/ManagePaid.template.php b/Themes/default/ManagePaid.template.php
index e9df4973f9..2659f703ac 100644
--- a/Themes/default/ManagePaid.template.php
+++ b/Themes/default/ManagePaid.template.php
@@ -211,12 +211,6 @@ function template_delete_subscription()
  */
 function template_modify_user_subscription()
 {
-	// Some quickly stolen javascript from Post, could do with being more efficient :)
-	echo '
-	<script>
-		var monthLength = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
-	</script>';
-
 	echo '
 	<form action="', Config::$scripturl, '?action=admin;area=paidsubscribe;sa=modifyuser;sid=', Utils::$context['sub_id'], ';lid=', Utils::$context['log_id'], '" method="post">
 		<div class="cat_bar">
@@ -257,7 +251,7 @@ function template_modify_user_subscription()
 			</dl>
 			<fieldset>
 				<legend>', Lang::$txt['start_date_and_time'], '</legend>
-				<select name="year" id="year" onchange="generateDays();">';
+				<select name="year" id="year">';
 
 	// Show a list of all the years we allow...
 	for ($year = 2005; $year <= 2030; $year++)
@@ -266,7 +260,7 @@ function template_modify_user_subscription()
 
 	echo '
 				</select>
-				<select name="month" id="month" onchange="generateDays();">';
+				<select name="month" id="month">';
 
 	// There are 12 months per year - ensure that they all get listed.
 	for ($month = 1; $month <= 12; $month++)
@@ -291,7 +285,7 @@ function template_modify_user_subscription()
 			</fieldset>
 			<fieldset>
 				<legend>', Lang::$txt['end_date_and_time'], '</legend>
-				<select name="yearend" id="yearend" onchange="generateDays(\'end\');">';
+				<select name="yearend" id="yearend">';
 
 	// Show a list of all the years we allow...
 	for ($year = 2005; $year <= 2030; $year++)
@@ -300,7 +294,7 @@ function template_modify_user_subscription()
 
 	echo '
 				</select>
-				<select name="monthend" id="monthend" onchange="generateDays(\'end\');">';
+				<select name="monthend" id="monthend">';
 
 	// There are 12 months per year - ensure that they all get listed.
 	for ($month = 1; $month <= 12; $month++)
@@ -336,6 +330,10 @@ function template_modify_user_subscription()
 			sSearchType: \'member\',
 			sTextDeleteItem: \'', Lang::$txt['autosuggest_delete_item'], '\',
 		});
+		document.getElementById("year").addEventListener("change", generateDays);
+		document.getElementById("month").addEventListener("change", generateDays);
+		document.getElementById("yearend").addEventListener("change", generateDays.bind(null, "end"));
+		document.getElementById("monthend").addEventListener("change", generateDays.bind(null, "end"));
 	</script>';
 
 	if (!empty(Utils::$context['pending_payments']))
diff --git a/Themes/default/ManageSearch.template.php b/Themes/default/ManageSearch.template.php
index 7f660a1e35..64cf9aa796 100644
--- a/Themes/default/ManageSearch.template.php
+++ b/Themes/default/ManageSearch.template.php
@@ -310,7 +310,7 @@ function template_create_index_progress()
 				</div>
 			</div>
 			<hr>
-			<input type="submit" name="b" value="', Lang::$txt['search_create_index_continue'], '" class="button">
+			<input type="submit" name="cont" value="', Lang::$txt['search_create_index_continue'], '" class="button">
 		</div>
 		<input type="hidden" name="step" value="', Utils::$context['step'], '">
 		<input type="hidden" name="start" value="', Utils::$context['start'], '">
@@ -318,23 +318,8 @@ function template_create_index_progress()
 		<input type="hidden" name="', Utils::$context['session_var'], '" value="', Utils::$context['session_id'], '">
 	</form>
 	<script>
-		var countdown = 10;
-		doAutoSubmit();
-
-		function doAutoSubmit()
-		{
-			if (countdown == 0)
-				document.forms.autoSubmit.submit();
-			else if (countdown == -1)
-				return;
-
-			document.forms.autoSubmit.b.value = "', Lang::$txt['search_create_index_continue'], ' (" + countdown + ")";
-			countdown--;
-
-			setTimeout(doAutoSubmit, 1000);
-		}
+		doAutoSubmit(10, ', Utils::escapeJavaScript(Lang::$txt['search_create_index_continue']), ');
 	</script>';
-
 }
 
 /**
diff --git a/Themes/default/Packages.template.php b/Themes/default/Packages.template.php
index 256c0c588f..4f520c3d94 100644
--- a/Themes/default/Packages.template.php
+++ b/Themes/default/Packages.template.php
@@ -1834,21 +1834,7 @@ function template_action_permissions()
 	// Just the countdown stuff
 	echo '
 	<script>
-		var countdown = ', $countDown, ';
-		doAutoSubmit();
-
-		function doAutoSubmit()
-		{
-			if (countdown == 0)
-				document.forms.perm_submit.submit();
-			else if (countdown == -1)
-				return;
-
-			document.getElementById(\'cont\').value = "', Lang::$txt['not_done_continue'], ' (" + countdown + ")";
-			countdown--;
-
-			setTimeout(doAutoSubmit, 1000);
-		}
+		doAutoSubmit(', $countDown, ', ', Utils::escapeJavaScript(Lang::$txt['not_done_continue']), '"perm_submit", "go");
 	</script>';
 }
 
diff --git a/Themes/default/Post.template.php b/Themes/default/Post.template.php
index 89d12c5d42..95262ee2ee 100644
--- a/Themes/default/Post.template.php
+++ b/Themes/default/Post.template.php
@@ -822,7 +822,7 @@ function template_announcement_send()
 				</div>
 				<hr>
 				<div id="confirm_buttons">
-					<input type="submit" name="b" value="', Lang::$txt['announce_continue'], '" class="button">
+					<input type="submit" name="cont" value="', Lang::$txt['announce_continue'], '" class="button">
 					<input type="hidden" name="', Utils::$context['session_var'], '" value="', Utils::$context['session_id'], '">
 					<input type="hidden" name="topic" value="', Utils::$context['current_topic'], '">
 					<input type="hidden" name="move" value="', Utils::$context['move'], '">
@@ -836,21 +836,7 @@ function template_announcement_send()
 	</div><!-- #announcement -->
 	<br>
 	<script>
-		var countdown = 2;
-		doAutoSubmit();
-
-		function doAutoSubmit()
-		{
-			if (countdown == 0)
-				document.forms.autoSubmit.submit();
-			else if (countdown == -1)
-				return;
-
-			document.forms.autoSubmit.b.value = "', Lang::$txt['announce_continue'], ' (" + countdown + ")";
-			countdown--;
-
-			setTimeout(doAutoSubmit, 1000);
-		}
+		doAutoSubmit(2, ', Utils::escapeJavaScript(Lang::$txt['announce_continue']), ');
 	</script>';
 }
 
diff --git a/Themes/default/scripts/paidsubs.js b/Themes/default/scripts/paidsubs.js
new file mode 100644
index 0000000000..0031dfce0a
--- /dev/null
+++ b/Themes/default/scripts/paidsubs.js
@@ -0,0 +1,41 @@
+function generateDays(offset = '') {
+	// Get the DOM elements
+	const dayElement = document.getElementById('day' + offset);
+	const yearElement = document.getElementById('year' + offset);
+	const monthElement = document.getElementById('month' + offset);
+
+	// Validate the existence of elements
+	if (!dayElement || !yearElement || !monthElement) {
+		console.error('One or more elements are missing. Ensure the IDs are correct.');
+		return;
+	}
+
+	// Month lengths (default February to 28 days)
+	const monthLengths = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
+
+	// Adjust February for leap years
+	const year = parseInt(yearElement.options[yearElement.selectedIndex]?.value || 0, 10);
+	if ((year % 4 === 0 && year % 100 !== 0) || (year % 400 === 0)) {
+		monthLengths[1] = 29;
+	}
+
+	// Get selected day before updating options
+	const selectedDay = dayElement.selectedIndex;
+
+	// Clear current options
+	dayElement.innerHTML = '';
+
+	// Get the number of days in the selected month
+	const daysInMonth = monthLengths[parseInt(monthElement.value, 10) - 1] || 31;
+
+	// Populate day options
+	for (let i = 1; i <= daysInMonth; i++) {
+		const option = document.createElement('option');
+		option.value = i;
+		option.textContent = i;
+		dayElement.appendChild(option);
+	}
+
+	// Restore the previously selected day if valid
+	dayElement.selectedIndex = Math.min(selectedDay, daysInMonth - 1);
+}
diff --git a/Themes/default/scripts/script.js b/Themes/default/scripts/script.js
index 960d12a9c0..bb707ad7d7 100644
--- a/Themes/default/scripts/script.js
+++ b/Themes/default/scripts/script.js
@@ -1485,35 +1485,6 @@ function expandThumb(thumbID)
 	return false;
 }
 
-function generateDays(offset)
-{
-	// Work around JavaScript's lack of support for default values...
-	offset = typeof(offset) != 'undefined' ? offset : '';
-
-	var days = 0, selected = 0;
-	var dayElement = document.getElementById("day" + offset), yearElement = document.getElementById("year" + offset), monthElement = document.getElementById("month" + offset);
-
-	var monthLength = [
-		31, 28, 31, 30,
-		31, 30, 31, 31,
-		30, 31, 30, 31
-	];
-	if (yearElement.options[yearElement.selectedIndex].value % 4 == 0)
-		monthLength[1] = 29;
-
-	selected = dayElement.selectedIndex;
-	while (dayElement.options.length)
-		dayElement.options[0] = null;
-
-	days = monthLength[monthElement.value - 1];
-
-	for (i = 1; i <= days; i++)
-		dayElement.options[dayElement.length] = new Option(i, i);
-
-	if (selected < days)
-		dayElement.selectedIndex = selected;
-}
-
 function initSearch()
 {
 	if (document.forms.searchform.search.value.indexOf("%u") != -1)
@@ -1992,4 +1963,33 @@ smc_preview_post.prototype.onDocSent = function (XMLDoc)
 	}
 
 	location.hash = '#' + this.opts.sPreviewSectionContainerID;
+}
+
+function doAutoSubmit(countdown, txtMessage, formName = 'autoSubmit', fieldName = 'cont') {
+	const form = document.forms[formName];
+
+	// Ensure the form exists
+	if (!form) {
+		console.error('Form with name "' + formName + '" not found.');
+		return;
+	}
+
+	// Handle the countdown completion
+	if (countdown <= 0) {
+		form.submit();
+		return;
+	}
+
+	// Update the field if it exists
+	const contField = form.elements[fieldName];
+	if (contField) {
+		contField.value = txtMessage + ' (' + countdown + ')';
+	} else {
+		console.warn('Field "' + fieldName + '" not found in form "' + formName + '".');
+	}
+
+	// Schedule the next countdown tick
+	setTimeout(() => {
+		doAutoSubmit(countdown - 1, txtMessage, formName, fieldName);
+	}, 1000);
 }
\ No newline at end of file