Home › Geometry › Date Duration Calculator
Date Duration Calculator
Pick both dates — the duration updates instantly.
Formula
days = (end − start) / 86,400,000 ms (exact calendar difference)
Examples
Jan 1 → Dec 31 (2026) = 364 days (2026 is not a leap year). A 90-day project from Mar 1 ends May 30.
FAQ
Does it count both endpoint days?
The result is the difference between the dates. If you want to include both the first and last day (e.g. rental days), add 1.
How are leap years handled?
Exactly — the calculation uses real calendar dates, so Feb 29 is counted when it occurs.