Subtract days, weeks, months or years from a date
Find out what date it was a given period before a reference date.
Calculator inputs
Results
Enter your values and press “Calculate” to see the result.
In short
- What it calculates
- Find out what date it was a given period before a reference date.
- Formula used
Earlier date = start date − amount × unit- Example
- 2026-03-15 − 15 days = 2026-02-28
Subtract days from a date
Use it to work out when to start something when the deadline is fixed: subtract the time you need and you get the start date.
It also helps reconstruct past dates.
How it works
The calculation mirrors addition: it moves back along the real calendar, respecting the length of each month and leap years.
Formula
Earlier date = start date − amount × unit
Worked example
2026-03-15 − 15 days = 2026-02-28
2026-03-31 − 1 month = 2026-02-28, because February has no 31st
Explanation
Planning backwards from a deadline
It is the natural way to organise any project with a fixed delivery. If the wedding is on 15 June and invitations must go out eight weeks earlier, subtracting gives the date they must be printed by. Chaining subtractions builds a full schedule from the end backwards.
Notice periods and legal deadlines
Notice of resignation, contract termination or non-renewal of a tenancy is counted backwards from the effective date. Delivering one day late can trigger a penalty or the automatic renewal of another full period, so count the exact days rather than trusting 'a month before'.
Expiries and renewals
Renewal notices for subscriptions, insurance and domains arrive with little warning, or not at all. Subtracting the notice period from the renewal date gives the last working day to cancel before another year is charged.
When the subtraction crosses the year
Subtracting ninety days from 15 February lands in mid-November of the previous year. The calculation handles it automatically, including the leap year adjustment.
Frequently asked questions
Can it work out a start date?
Yes. If delivery is 30 June and you need 45 days of work, subtract 45 days to see when to begin.
Can the result fall in another year?
Yes, with no problem. The calculation crosses year boundaries correctly.
How do I work out my notice deadline?
By subtracting the notice period from the effective date. For fifteen calendar days, subtract fifteen from the date you want it to take effect.
Does subtraction work across years?
Yes. The calculation moves into the previous year without difficulty and accounts for leap years.
Need to calculate something else?
These tools are often used alongside this calculator.
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Count the days remaining (or elapsed) between today and the date you choose.