iCalendar RRULE Generator - RFC 5545 Recurrence Rules

Build iCalendar recurrence rules visually. Supports BYMONTHDAY -1 for last day of month, BYSETPOS for nth weekday. RFC 5545 compliant RRULE generator.

RRULE Builder

Frequency

Interval

Every month(s)

Monthly Pattern

Day of Month

Use negative values for days from end: -1 = last day, -2 = second to last

End

Week Start (WKST)

Generated RRULE

Start Date (DTSTART)

RRULE:FREQ=MONTHLY;BYMONTHDAY=-1

Every month on the last day

Next Occurrences

Parse Existing RRULE

Common Patterns

CSS Grid Generator - Visual Layout Build…

Fake Data Generator - Create Test Data I…

CSS Gradient Generator - Linear, Radial …

CSS Flexbox Generator - Visual Layout Bu…

JSON to TypeScript - Type Generator Onli…

View all Dev generators →

Frequently Asked Questions

RRULE (Recurrence Rule) is a property defined in RFC 5545 that specifies how calendar events repeat. It's used by Google Calendar, Outlook, Apple Calendar, and all iCalendar-compatible applications to define recurring events like 'every Monday' or 'last day of each month'.

In RFC 5545, negative values in BYMONTHDAY count backwards from month end. BYMONTHDAY=-1 means the last day, BYMONTHDAY=-2 means second-to-last. Example: FREQ=MONTHLY;BYMONTHDAY=-1 runs on the last day of every month, whether that's the 28th, 29th, 30th, or 31st.

BYDAY specifies which days of the week (MO, TU, WE, TH, FR, SA, SU). BYSETPOS filters which occurrence within the period. For 'last Friday of month', use FREQ=MONTHLY;BYDAY=FR;BYSETPOS=-1. For 'first Monday', use FREQ=MONTHLY;BYDAY=MO;BYSETPOS=1.

Use FREQ=MONTHLY;BYDAY=FR;BYSETPOS=-1. BYDAY=FR selects all Fridays in the month, then BYSETPOS=-1 picks the last one. This works correctly regardless of how many Fridays are in that month.

WKST (Week Start) defines which day starts the week, affecting WEEKLY frequency and BYWEEKNO calculations. Default is MO (Monday). Use WKST=SU for Sunday-start weeks. Important for rules like 'every 2 weeks' to ensure consistent week boundaries.

COUNT specifies how many occurrences total (e.g., COUNT=10 for exactly 10 events). UNTIL specifies an end date (e.g., UNTIL=20251231T235959Z). Use COUNT for fixed number of occurrences, UNTIL for date-based ending. Don't use both together.

Common issues: UNTIL must be in UTC with Z suffix (UNTIL=20251231T235959Z), BYDAY values must be uppercase (MO not mo), and some apps don't support all RFC 5545 features. Test your RRULE in this generator to see computed occurrences.

Use FREQ=WEEKLY;BYDAY=MO,TU,WE,TH,FR for every weekday. For every other week on weekdays, add INTERVAL=2. You can also combine with specific times using DTSTART in your calendar event.

Yes, comma-separate them. BYMONTHDAY=1,15 runs on the 1st and 15th. BYMONTHDAY=1,-1 runs on the first and last day. This is useful for semi-monthly schedules like payroll dates.

For quarterly, use FREQ=MONTHLY;INTERVAL=3 or FREQ=YEARLY;BYMONTH=1,4,7,10. For semi-annual, use FREQ=MONTHLY;INTERVAL=6 or FREQ=YEARLY;BYMONTH=1,7. Add BYMONTHDAY for specific days within those months.

RRULE Builder

Generated RRULE

Next Occurrences

Parse Existing RRULE

Common Patterns

Related Tools