Date Add / Subtract Calculator
Add or subtract years, months, weeks, and days from any date.
How to use this calculator
- Pick the start date and choose Add or Subtract.
- Fill in any combination of years, months, weeks, and days; leave others at 0.
- The result shows the date, its weekday, and the total day distance.
How it works
Years and months are applied first, then weeks and days. This ordering matters: '1 month + 5 days' moves to the same day-of-month next month, then adds 5 days.
Month-end clamping: January 31 + 1 month lands on February 28 (or 29 in a leap year), because February has no 31st.
Worked example
A contract requires notice 90 days before December 31, 2026.
- 1Choose Subtract, days = 90
- 2December has 31 days; count back 90 days through November and October
October 2, 2026 (a Friday).
When this calculator is useful
- Contract and notice deadlines
- Medication and follow-up scheduling
- Counting forward from a start date
- Answering "what date is 45 days from now?"
Frequently asked questions
What is January 31 plus one month?
February 28 (or 29 in a leap year). The date clamps to the last day of the target month rather than rolling into March.
Why does the order of months vs days matter?
Months have variable lengths. Adding a month then 5 days can differ from adding 5 days then a month; this calculator applies years and months first, matching common legal and billing conventions.