Recurring Event Date Calculator
Many events repeat on a fixed cycle: fortnightly meetings, monthly bills, quarterly reviews, yearly anniversaries. This calculator finds the exact date of any occurrence in such a series. Give it the first occurrence date, how often the event repeats in days, weeks, months, or years, and the occurrence number you want, and it returns that date along with the occurrences immediately before and after. Month and year intervals follow standard date arithmetic, which is worth noting when your start date is near the end of a month, since a short target month rolls the day forward.
Recurring date formula
steps = (occurrence number - 1) * interval
days unit: date = start + steps days
weeks unit: date = start + steps * 7 days
months unit: date = start + steps months
years unit: date = start + steps years
Occurrence 1 is the start date. Each later occurrence adds the interval the appropriate number of times. Month and year additions keep the day number where possible and otherwise roll into the next month under standard date rules.
Recurrence notes
- Occurrence 1 equals the first occurrence date you enter.
- Use weeks for fortnightly (every 2 weeks) schedules.
- Month-end start dates can shift when a target month is shorter.
- The interval and occurrence number must be whole numbers of 1 or more.
- Previous and next occurrences show the surrounding cycle.
Recurring event date: frequently asked questions
How does the recurring date calculator work?
You set a first occurrence date, choose how often the event repeats, and pick which occurrence you want. The calculator adds the interval the right number of times to the start date and returns the date of that occurrence, plus the date of the one before and after it.
What interval units can I use?
You can repeat by days, weeks, months, or years, with any whole-number interval. For example, every 2 weeks for a fortnightly meeting, every 3 months for a quarterly review, or every 1 year for an anniversary. Weeks are treated as seven-day blocks.
How are month intervals handled near month end?
Adding months keeps the same day number when it exists. If the target month is shorter, for example adding one month to 31 January, the result rolls into the following month, which is the standard behavior of date arithmetic. Watch for this when your start date is the 29th, 30th, or 31st.
What does occurrence number mean?
Occurrence 1 is the first occurrence, which is the start date itself. Occurrence 2 is one interval later, occurrence 3 is two intervals later, and so on. So the Nth occurrence is the start date plus the interval multiplied by N minus 1.
Can I use this for billing or subscription dates?
Yes. It is well suited to working out future billing dates, subscription renewals, payroll runs, maintenance schedules, and any other event that repeats on a fixed interval. The previous and next occurrence outputs help you see the surrounding cycle at a glance.
Official sources
- International Organization for Standardization: ISO 8601 date and time format (includes recurring interval notation).
- NIST Time and Frequency Division: Time and Frequency.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.