Time calculator
Date Add/Subtract Calculator
Move a calendar date forward or backward by days, weeks, months, or years.
Resulting date
February 28, 2025
How the date add/subtract calculator works
Days and weeks use calendar-day movement, with one week equal to seven days. Months and years first move to the target month, then clamp the original day to the last valid day there.
Clamping prevents JavaScript overflow surprises: adding one month to January 31 becomes the final day of February rather than spilling into March.
Worked example
Starting at February 29, 2024 and adding one year first targets February 2025. Because 2025 is not a leap year, February has only 28 days, so the result is February 28, 2025.
Assumptions and practical limits
Month-end clamping is a stated convention; some billing systems use different end-of-month rules. Verify contractual schedules independently.
The operation uses local civil dates at noon to reduce daylight-saving boundary problems. It does not add exact 24-hour durations.
Frequently asked questions
What is one month after January 31?
The result is the last valid day of February: February 28 or 29 depending on the year.
How are weeks calculated?
One week is exactly seven calendar days.
Can I subtract an interval?
Yes. Choose Subtract and enter a positive amount.