Date Duration Calculator

The duration between two dates sounds like it should have one obvious answer, but “duration” actually means several genuinely different things depending on what you’re asking. This tool gives you all of them at once, rather than picking one and hiding the rest: an exact calendar breakdown (years, months, and days, calculated the way a person would count on a calendar), flat totals (total days, weeks, months, and years, as single numbers), and an optional business-days count (weekdays only, for anything scoped in working days rather than calendar time).

The exact breakdown is calendar-anchored, not a fixed-length unit — it’s built by walking real calendar months and years, so “1 month” always means one real month’s worth of days, whichever month that happens to be (28 to 31 days), not a fixed 30-day placeholder. This is exact, but it does mean a month-length mismatch has to be resolved somehow: January 31 to February 28 has no clean “one month” answer, since February has no 31st for the anchor to land on. This tool resolves that case to the actual elapsed days (28) rather than forcing a fractional or rounded month — documented honestly in the FAQ below as a real convention choice, not presented as the one obviously correct answer, since a different convention could reasonably resolve it differently.

Total Months and Total Years are a different, separately useful kind of number: averages, not calendar counts. They’re computed as total days divided by the Gregorian calendar’s average month length (30.436875 days) and average year length (365.2425 days) — the same average a leap-year cycle produces over 400 years. This answers “roughly how many months/years is this” as one clean decimal figure, which is exactly what the exact breakdown deliberately doesn’t try to do (a calendar breakdown can’t cleanly express “1.8 years” as a single number — it gives you “1 year, 9 months, 12 days” instead). Both numbers are computed from the same real, leap-year-aware day count; they’re just answering different questions.

Negative durations (end date before start date) always compute, never error. A visible notice appears above the results in that case, and every number shown — total days, the breakdown, business days — is the positive size of the span between the two dates, not a signed negative number that could be misread. Business days count weekdays strictly after the start date, up to and including the end date (a Friday to the following Monday is 1 business day, since Saturday and Sunday fall in between and the start date itself is where you’re counting from, not an elapsed day) — public holidays aren’t excluded, since holiday calendars vary by country and this tool has no way to know which one applies.

Every calculation runs on real calendar math, including real leap years — no approximation smooths over a February 29, and every date field is handled as a plain calendar date (no time-of-day component), so a duration spanning a daylight-saving transition is never off by an hour at the boundary. Nothing is sent anywhere: both dates and every result stay in your browser.