Date calculator
Add months without tripping over month-end. Subtract across a leap year. Shift a clock time past midnight and see which day it lands on.
Common questions
What can this calculator do?
Three things: add or subtract days, weeks or months from any date; find the interval between two moments in time; and answer "what time was it N hours ago" style questions. Each mode shows its working.
Is this a time calculator?
It handles the date-and-time arithmetic most people need: time-of-day shifts across midnight, durations between timestamps. If you need running stopwatch timers, a dedicated time calculator does that — we deliberately do not chase that head term.
How are months added?
Calendar months with month-end clamping: January 31 plus one month is February 28 (or 29), not March 3. This matches banking and billing practice.
Last updated 2026-11-04 · Calculations follow the full leap-year rule (including the year 2100 exception).