diff --git a/assets/js/calendar.js b/assets/js/calendar.js
index 5aa9d6b..ffb3c7e 100644
--- a/assets/js/calendar.js
+++ b/assets/js/calendar.js
@@ -131,6 +131,12 @@ document.addEventListener('DOMContentLoaded', function() {
             else if (rruleStr.includes("FREQ=MONTHLY") && rruleStr.includes("BYDAY")) {
                 const bydayMatch = rruleStr.match(/BYDAY=([^;]+)/);
                 if (bydayMatch) {
+                    const intervalMatch = rruleStr.match(/INTERVAL=(\d+)/);
+                    const interval = intervalMatch ? parseInt(intervalMatch[1]) : 1;
+                    const monthsFromStart = (year - startDate.getFullYear()) * 12 + (month - startDate.getMonth());
+                    if (monthsFromStart < 0 || monthsFromStart % interval !== 0) {
+                        return [];
+                    }
                     const bydays = bydayMatch[1].split(',');
                     const dayMap = {
                         'MO': 1, 'TU': 2, 'WE': 3, 'TH': 4, 'FR': 5, 'SA': 6, 'SU': 0