Add your input
A start date, an amount, and a calendar unit.
Time keeper
Date add subtract calculator
Shift a date by a set interval with a stated end-of-month rule.
Privacy built inYour work stays with you
Common intervals
Add 1 month from 1/31/2026
Resulting date
2/28/2026
The target month has no day 31, so the result moved to its last day.
Days from start
28
Your work stays private in your browser while you use this tool.
What does date add subtract calculator do?
The date add subtract calculator shifts an ISO calendar date forward or back by a whole number of days, weeks, months, or years and reports the resulting date. Month and year steps clamp to the last day of the target month when the original day does not exist there, so 31 January plus one month is 28 February in a common year.
- Input
- A start date, an amount, and a calendar unit.
- Result
- The resulting date with the calculation written out.
- Price
- Free
- Account
- Not required
How to use date add subtract calculator
Choose your settings
Shift a date by a set interval with a stated end-of-month rule.
Save or copy
The resulting date with the calculation written out.
A practical tip
Month and year steps land on the last day of the target month when the original day does not exist.
When to use date add subtract calculator
Work out a payment due date thirty days after an invoice is issued.
Find the end of a six-month notice period from a contract start date.
Check which date falls ninety days before a deadline without counting on a calendar.
Worked example
A concrete date add subtract calculator example
- Input
- Start: 2026-01-31; add 1 month
- Result
- 2026-02-28, clamped from the 31st because February has no 31st day.
What to expect
How it works
The start date is validated as YYYY-MM-DD and held at UTC midnight, so a daylight-saving transition between the two dates cannot move the displayed day. Day and week steps add a fixed number of UTC days. Month and year steps move the month index instead, then clamp the day to the last day of the target month, which is what makes the operation total for every input.
Know before using
Limits and edge cases
- Month and year arithmetic is not reversible at month ends: 31 January plus one month is 28 February, and subtracting one month from that result returns 28 January rather than the original 31st.
- The result is a calendar date only. It carries no time of day, so it cannot express a deadline that falls at a particular hour in a particular time zone.
Standards and sources
Common questions
Date add subtract calculator FAQ
Is date add subtract calculator free to use?
Yes. Date add subtract calculator is free to use.
Does date add subtract calculator keep my work private?
Yes. Your work stays private while you use the tool — nothing you enter is uploaded.
What does the tool return for 31 January plus one month?
28 February in a common year and 29 February in a leap year. The day is clamped to the last day of the target month because no 31 February exists, which is the same rule spreadsheets apply.
Does adding one year to 29 February give 28 February or 1 March?
28 February. The same end-of-month clamp applies to year steps, so the result stays inside the target month rather than rolling into the next one.