# ICS Calendar Recurrence Rule Expander Expand RRULE-based VEVENT recurrence into concrete occurrences and export them as JSON or a flattened ICS calendar > Canonical page: https://elysiatools.com/en/tools/ics-calendar-recurrence-rule-expander - **Category:** Date & Time - **Keywords:** ics, ical, rrule, calendar, recurrence, vevent ## Overview Paste a full .ics payload or a single VEVENT block, then expand its RRULE into concrete event instances. The tool understands common RRULE parts including FREQ, INTERVAL, COUNT, UNTIL, BYDAY, and BYMONTHDAY. How to fill the form: - ICS or VEVENT Input: paste the calendar text directly - ICS File: upload a .ics file instead of pasting - Timezone Override: optionally attach a timezone label to the exported calendar header - Holiday Dates: provide YYYY-MM-DD dates, one per line, to exclude occurrences on those days - Max Occurrences: safety cap for expansion when the RRULE has no COUNT - Output Format: return JSON, ICS, or both in the result payload Current scope: - Expands the first VEVENT found in the input - Supports DAILY, WEEKLY, MONTHLY, and YEARLY frequencies - Uses UTC-style normalization for generated output ## Inputs - **ICS or VEVENT Input** (textarea): BEGIN:VEVENT DTSTART:20260401T090000Z DTEND:20260401T100000Z RRULE:FREQ=WEEKLY;BYDAY=MO,WE;COUNT=6 SUMMARY:Team sync END:VEVENT - **ICS File** (file) - **Timezone Override** (text): Asia/Shanghai - **Holiday Dates** (textarea): 2026-05-01 2026-10-01 - **Max Occurrences** (number) - **Output Format** (select) ## When to use - When you need to extract a flat list of explicit dates and times from a complex iCalendar recurrence rule (RRULE). - When migrating calendar data to a system, database, or legacy CRM that does not natively support parsing RRULE logic. - When you want to generate a static calendar file that automatically skips specific holidays or blackout dates. ## How it works - Paste your raw ICS text, a single VEVENT block, or upload an .ics file containing the recurrence rule. - Optionally define a timezone override, set a maximum occurrence limit, and list specific holiday dates (YYYY-MM-DD) to exclude. - Select your preferred output format (JSON, ICS, or both) and run the tool. - The tool parses the RRULE, calculates the concrete event instances, and outputs the flattened schedule. ## Use cases - Flattening a recurring weekly team meeting into a JSON array for a custom dashboard display. - Converting a yearly subscription renewal schedule into explicit billing dates for a database import. - Generating a static ICS file for a school semester schedule that automatically excludes public holidays. ## Frequently asked questions ### Which recurrence frequencies are supported? The tool supports DAILY, WEEKLY, MONTHLY, and YEARLY frequencies, including common rule parts like INTERVAL, COUNT, UNTIL, BYDAY, and BYMONTHDAY. ### Can I process multiple events at once? Currently, the tool parses and expands only the first VEVENT block found in your input. ### How do the holiday exclusions work? By entering dates in YYYY-MM-DD format (one per line), the tool will automatically skip generating an occurrence if it falls on any of those specified dates. ### What happens if my recurrence rule goes on forever? If your RRULE lacks a COUNT or UNTIL parameter, the tool uses the 'Max Occurrences' setting (defaulting to 100) as a safety cap to prevent infinite loops. ### What output formats can I choose? 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