Date Calculator
Add or subtract days, weeks, months or years from a date.
Finding a date from another
Working out what date falls a certain time before or after a known date — thirty days from now, three months ago, a year from a start date — is a common need. This adds or subtracts a period from a date, handling the calendar's irregularities for you.
Enter a date and a period to add or subtract.
Why date arithmetic is harder than it looks
Dates are genuinely awkward to calculate by hand because the calendar is irregular: months have different lengths, leap years add a day, and adding months raises tricky questions, like what a month after the 31st of January should be when February has no 31st. Counting days across month and year boundaries by hand is exactly where mistakes creep in. The calculation handles all of this — the varying month lengths, leap years, and the boundary crossings — to give the correct date. This matters for deadlines, contract dates, subscription renewals, planning ahead, and any situation where you need to know precisely what date lands a given period from another, which the calendar's irregularity makes surprisingly error-prone to work out in your head.
Common questions
Why is adding to a date tricky?
Because the calendar is irregular — months differ in length, leap years add a day, and adding months across boundaries raises questions like a month after 31 January.
What is it useful for?
Deadlines, contract and renewal dates, and planning — anywhere you need the exact date a given period before or after another.
Is anything uploaded?
No. The calculation happens in your browser.