Input
Preparing your workspace…
How to use
- Enter the starting date, time and zone.
- Choose Add or Subtract and set an amount, or combine units in Advanced.
- Review the result, then copy, download or use it as the next starting date.
Adding calendar units and time
Adding a month follows the calendar, while adding a fixed number of hours follows elapsed time. These can produce different local results near month ends and daylight-saving changes.
Use one amount and unit for a simple calculation, or combine units in Advanced. The result can become the starting point of a further calculation.
Calendar and clock adjustments
Years and months move through the calendar; weeks and days retain local calendar meaning. Hours, minutes and seconds then adjust elapsed time. Combined adjustments apply in that order.
2026-01-31 + P1M · UTC2026-02-28T00:00:00ZA fixed example; the time zone and precision are part of the calculation.
Month ends and clock transitions
If a destination month has no matching day, Constrain uses its last valid day and Reject reports an error. Missing or repeated destination clock times follow the selected DST-resolution setting.
Continuing a calculation
Use result as start applies the computed local date and offset to the next calculation. Copy and JSON download let you keep the result separately without changing the original input outside this page.
ISO calendar dates, nanosecond precision and explicit time zones. Cron uses five fields, up to 50 runs within 10 years, reference years 1900–2199 and a 5-second processing limit. Time-zone data comes from your browser. Processing stays on your device.
Frequently asked questions
Is adding one day the same as adding 24 hours?
Not always. A day is a calendar step; 24 hours is elapsed time. They can differ across a daylight-saving transition.
What happens to January 31 plus one month?
With Constrain, the result is the last valid day in February. With Reject, the unavailable day produces an error.
Can I combine months and days?
Yes. Open Advanced and set multiple units. Calendar adjustments are applied before the elapsed-time units.
Can I calculate a sequence of offsets?
Yes. Use result as start, then choose the next adjustment. Copy or download intermediate results if you need a record of the sequence.
Does this skip weekends or holidays?
No. All calendar days are eligible. There is no business-day or regional holiday adjustment.