Advanced date and time calculationsElapsed time with zones, clock differences, averages, sorting and interval splitting.
Details of the first result
Dates & time
How it works
Calendar months vary in length. Adding a month is different from adding 30 days. Jan31 plus one month needs a rule because February has no 31st.
What you can do
Add or subtract years, months, weeks and days with an explicit rule for missing month-end dates.
How to use it
- Enter a YYYY-MM-DD date. Choose add or subtract and fill nonnegative years, months, weeks and days. Choose the last valid day or reject missing dates. Calculate to see the resulting date, weekday and day distance.
- Check the result and its notes. Copy or download only after calculating; any edit clears the old result.
Errors and limits
Years and months are applied together first, then weeks and days. Constraining a month-end is highlighted. The calculation uses calendar days without time zones, business-day exclusions, or legal deadline rules.
All input stays in this tab. TXT files must be UTF-8; bulk input is limited to 200,000 characters and 10,000 lines.
Extensions: year searches ≤500years; date patterns ≤200,000days; clock patterns ≤24hours; result ≤10,000rows. Magic digits mean all equal or ascending with9→0 wrap. Choose the digit representation explicitly. Rounding ties choose the later boundary; ISO weeks start Monday. Date templates: [YYYY] [MM] [DD] [DDD] [W] [E]; clocks: [HH] [hh] [mm] [ss] [A]. Natural-language output uses your interface language. Gregorian Easter:1583–4099. Interval input: start / end.
Frequently asked questions
What happens to January 31 plus one month?
With the last-valid-day rule, it becomes Feb29 in 2024 or Feb28 in 2025. Reject mode stops and explains the missing day. Adding a second month from the constrained result can differ from adding two months at once.
Are my dates uploaded or saved?
No. These calculations run in your browser. Inputs are not added to the address, stored between visits or sent to a server. Copy and download save only when you ask.