diff --git a/calendar/base/modules/Ical.sys.mjs b/calendar/base/modules/Ical.sys.mjs
index f3878ec1f65..d4ff01cd51b 100644
--- a/calendar/base/modules/Ical.sys.mjs
+++ b/calendar/base/modules/Ical.sys.mjs
@@ -446,8 +446,20 @@ class Duration {
       let str = "";
       if (this.isNegative) str += "-";
       str += "P";
-      if (this.weeks) str += this.weeks + "W";
-      if (this.days) str += this.days + "D";
+      console.log(this.weeks)
+      if(this.weeks){
+        if (this.days || this.hours || this.minutes || this.seconds){
+          str += (this.weeks*7 + this.days + "D");
+        }
+        else{
+          str += (this.weeks + "W");
+        }
+      }
+      else{
+        if(this.days){
+          str += (this.days + "D");
+        }
+      }
 
       if (this.hours || this.minutes || this.seconds) {
         str += "T";
diff --git a/calendar/test/unit/test_duration_rfc.js b/calendar/test/unit/test_duration_rfc.js
new file mode 100644
index 00000000000..9418718976a
--- /dev/null
+++ b/calendar/test/unit/test_duration_rfc.js
@@ -0,0 +1,141 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+ var { XPCOMUtils } = ChromeUtils.importESModule("resource://gre/modules/XPCOMUtils.sys.mjs");
+
+ ChromeUtils.defineESModuleGetters(this, {
+   CalAlarm: "resource:///modules/CalAlarm.sys.mjs",
+   CalAttachment: "resource:///modules/CalAttachment.sys.mjs",
+   CalAttendee: "resource:///modules/CalAttendee.sys.mjs",
+   CalTodo: "resource:///modules/CalTodo.sys.mjs",
+   CalDateTime: "resource:///modules/CalDateTime.sys.mjs",
+ });
+
+ function run_test() {
+    // Time break up values
+    weeks = 604800;
+    days = 86400;
+    hours = 3600;
+    minutes = 60;
+    seconds = 1;
+
+    // Test weeks and hours
+    alarm = new CalAlarm();
+    alarm.related = Ci.calIAlarm.ALARM_RELATED_ABSOLUTE;
+    alarm.alarmDate = cal.createDateTime();
+    alarm.repeat = 1;
+    alarm.repeatOffset = cal.createDuration();
+    alarm.repeatOffset.inSeconds = (weeks * 0 + days * 0 + hours * 170 + minutes * 0 + seconds * 0);
+    console.log(alarm.mDuration.innerObject)
+    //console.log(date)
+    let caldate = new CalDateTime(alarm.mDuration.innerObject.clone())
+    console.log(caldate.toString())
+    equal(caldate.toString(), "P7DT2H")
+    delete alarm;
+    delete caldate;
+
+    // Test weeks and minutes
+    alarm = new CalAlarm();
+    alarm.related = Ci.calIAlarm.ALARM_RELATED_ABSOLUTE;
+    alarm.alarmDate = cal.createDateTime();
+    alarm.repeat = 1;
+    alarm.repeatOffset = cal.createDuration();
+    alarm.repeatOffset.inSeconds = (weeks * 1 + days * 0 + hours * 0 + minutes * 1 + seconds * 0);
+    console.log(alarm.mDuration.innerObject)
+    //console.log(date)
+    caldate = new CalDateTime(alarm.mDuration.innerObject.clone())
+    console.log(caldate.toString())
+    equal(caldate.toString(), "P7DT1M")
+    delete alarm;
+    delete caldate;
+
+    // Test weeks and seconds
+    alarm = new CalAlarm();
+    alarm.related = Ci.calIAlarm.ALARM_RELATED_ABSOLUTE;
+    alarm.alarmDate = cal.createDateTime();
+    alarm.repeat = 1;
+    alarm.repeatOffset = cal.createDuration();
+    alarm.repeatOffset.inSeconds = (weeks * 1 + days * 0 + hours * 0 + minutes * 0 + seconds * 30);
+    console.log(alarm.mDuration.innerObject)
+    //console.log(date)
+    caldate = new CalDateTime(alarm.mDuration.innerObject.clone())
+    console.log(caldate.toString())
+    equal(caldate.toString(), "P7DT30S")
+    delete alarm;
+    delete caldate;
+
+    // Test weeks, days, and hours
+    alarm = new CalAlarm();
+    alarm.related = Ci.calIAlarm.ALARM_RELATED_ABSOLUTE;
+    alarm.alarmDate = cal.createDateTime();
+    alarm.repeat = 1;
+    alarm.repeatOffset = cal.createDuration();
+    alarm.repeatOffset.inSeconds = (weeks * 5 + days * 2 + hours * 1 + minutes * 0 + seconds * 0);
+    console.log(alarm.mDuration.innerObject)
+    //console.log(date)
+    caldate = new CalDateTime(alarm.mDuration.innerObject.clone())
+    console.log(caldate.toString())
+    equal(caldate.toString(), "P37DT1H")
+    delete alarm;
+    delete caldate;
+
+    // Test weeks, days, and minutes
+    alarm = new CalAlarm();
+    alarm.related = Ci.calIAlarm.ALARM_RELATED_ABSOLUTE;
+    alarm.alarmDate = cal.createDateTime();
+    alarm.repeat = 1;
+    alarm.repeatOffset = cal.createDuration();
+    alarm.repeatOffset.inSeconds = (weeks * 5 + days * 2 + hours * 0 + minutes * 5 + seconds * 0);
+    console.log(alarm.mDuration.innerObject)
+    //console.log(date)
+    caldate = new CalDateTime(alarm.mDuration.innerObject.clone())
+    console.log(caldate.toString())
+    equal(caldate.toString(), "P37DT5M")
+    delete alarm;
+    delete caldate;
+
+    // Test weeks, days, and seconds
+    alarm = new CalAlarm();
+    alarm.related = Ci.calIAlarm.ALARM_RELATED_ABSOLUTE;
+    alarm.alarmDate = cal.createDateTime();
+    alarm.repeat = 1;
+    alarm.repeatOffset = cal.createDuration();
+    alarm.repeatOffset.inSeconds = (weeks * 5 + days * 2 + hours * 0 + minutes * 0 + seconds * 20);
+    console.log(alarm.mDuration.innerObject)
+    //console.log(date)
+    caldate = new CalDateTime(alarm.mDuration.innerObject.clone())
+    console.log(caldate.toString())
+    equal(caldate.toString(), "P37DT20S")
+    delete alarm;
+    delete caldate;
+
+    // Test days
+    alarm = new CalAlarm();
+    alarm.related = Ci.calIAlarm.ALARM_RELATED_ABSOLUTE;
+    alarm.alarmDate = cal.createDateTime();
+    alarm.repeat = 1;
+    alarm.repeatOffset = cal.createDuration();
+    alarm.repeatOffset.inSeconds = (weeks * 0 + days * 2 + hours * 0 + minutes * 0 + seconds * 0);
+    console.log(alarm.mDuration.innerObject)
+    //console.log(date)
+    caldate = new CalDateTime(alarm.mDuration.innerObject.clone())
+    console.log(caldate.toString())
+    equal(caldate.toString(), "P2D")
+    delete alarm;
+    delete caldate;
+
+    // Test only time
+    alarm = new CalAlarm();
+    alarm.related = Ci.calIAlarm.ALARM_RELATED_ABSOLUTE;
+    alarm.alarmDate = cal.createDateTime();
+    alarm.repeat = 1;
+    alarm.repeatOffset = cal.createDuration();
+    alarm.repeatOffset.inSeconds = (weeks * 0 + days * 0 + hours * 2 + minutes * 3 + seconds * 5);
+    console.log(alarm.mDuration.innerObject)
+    //console.log(date)
+    caldate = new CalDateTime(alarm.mDuration.innerObject.clone())
+    console.log(caldate.toString())
+    equal(caldate.toString(), "PT2H3M5S")
+    delete alarm;
+    delete caldate;
+  }
\ No newline at end of file
diff --git a/calendar/test/unit/xpcshell.toml b/calendar/test/unit/xpcshell.toml
index be81925469f..e0f3939b9dd 100644
--- a/calendar/test/unit/xpcshell.toml
+++ b/calendar/test/unit/xpcshell.toml
@@ -78,6 +78,8 @@ tags = ["oauth"]
 
 ["test_duration.js"]
 
+["test_duration_rfc.js"]
+
 ["test_email_utils.js"]
 
 ["test_extract.js"]