Date calculator
Calculate calendar dates and differences.
Your input stays on this device. Nothing is uploaded or saved.
About Date calculator
Add calendar years, months, weeks or days, or measure the calendar difference between two dates.
When to use it
Test renewals, leap years and month end expiry dates.
2028-01-31 + P1M → 2028-02-29How to use it
- Enter a start date.
- Choose an ISO duration such as P1M or an end date.
- Inspect the resulting date, weekday and calendar difference.
Use calendar arithmetic for calendar rules
Add ISO date durations such as P1M, P2W or -P10D to a Gregorian date. Month and year arithmetic constrains an invalid day to the last valid day of the destination month. For example, adding one month to January 31 can produce February 28 or 29 rather than overflowing into March.
Difference mode reports whole days and a calendar duration between two dates, including negative results when the end precedes the start. Dates have no timezone or clock time here. Use the timezone converter for exact instants and daylight saving behavior; a calendar day is not always twenty four elapsed hours.
Limits & privacy
Date only, Gregorian calendar. Durations up to 10,000 years, with no time component or fractional values. Month ends are constrained to the last valid day. Differences are calendar dates, not elapsed hours across daylight saving changes.
Use this tool from the API reference or connect through the SDK, CLI, SSH, or MCP. Hosted calls share your plan allowances.