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Date Difference Calculator
Pick two dates — see the exact gap.
Why date math is tricky
Months have unequal lengths so "1 month" is not always the same number of days. The calculator shows both calendar logic (years/months/days) and an exact total day count.
Leap years
A year is a leap year if divisible by 4 — except century years, which must also be divisible by 400. The day count handles this automatically.
Frequently asked questions
Does it count the start day?
No — end minus start, not including the start day. Add 1 to include both endpoints.
Can I calculate past dates?
Yes. Any dates in the Common Era work — the calculator uses calendar arithmetic, not Unix timestamps.
Why don't years×365+months×30+days equal the total days?
Because months and years have variable lengths. The exact day count is always the authoritative figure.
How do I calculate days until an event?
Set start = today, end = event date. Or use the Countdown Timer for a live display.