Days Between Dates Calculator

How many days is it from one date to another? The question sounds trivial until you try it by hand across a month boundary, a leap year, or both. The calculator above takes two dates and gives you the interval in days, and in weeks plus leftover days.

How it works

Enter a start date and an end date. The end date defaults to today, so the common case — "how long ago was that?" — is one click. The tool reports:

• Days — the number of days in the interval.
• Weeks and days — the same figure expressed as whole weeks with a remainder, which is usually easier to hold in your head. 45 days is 6 weeks and 3 days.

The result is order-independent: swapping the two dates gives the same positive number rather than a negative one.

This is an interval, measured between the two midnights, so the endpoints are not both counted. From the 1st to the 8th is 7 days. If you need the inclusive count — "how many days does this cover, including both the first and the last?" — add one. The distinction matters for hotel nights versus days of a conference, and for notice periods, where the wording of the contract decides which one applies.

Why the arithmetic is fiddly

Dates are parsed as local midnight rather than UTC. Parsing 2026-03-15 as a UTC instant and then reading it back in a local time zone west of Greenwich yields the 14th, and a whole class of "the date is one day out" bugs comes from exactly that. Keeping both ends in the same local frame removes it.

Daylight saving is the other trap. A day is not always 86,400 seconds: twice a year one is 23 hours long and one is 25. Dividing a raw millisecond difference by 86,400,000 therefore drifts by a fraction of a day across a transition, which is why the result here is rounded to the nearest whole day — that rounding is what makes a DST-crossing interval come out right rather than off by one.

Leap years are handled by the underlying calendar, not by a rule of thumb. The rule itself is worth knowing: every year divisible by 4 is a leap year, except centuries, except centuries divisible by 400. 2000 was a leap year; 1900 and 2100 are not.

Doing this in code

Do not write the subtraction yourself. Every mainstream platform has a date-only type that handles month lengths, leap years and DST for you — LocalDate and ChronoUnit.DAYS.between(...) in Java, date in Python, DATEDIFF in SQL. Optional and the date-time API covers the distinction between a LocalDate, a LocalDateTime and an Instant, and why picking the wrong one is the root cause of most date bugs.

Storage is the other half of the problem. A timestamp column without a time zone, populated from application servers in two regions, is unrecoverably ambiguous; a date-only column compared against a timestamp forces an implicit cast that quietly disables the index. SQL best practices covers choosing temporal types and writing range predicates that the planner can actually use.

Related tools

For a countdown to a future date, the days until date tool phrases the same calculation as "days remaining". To exclude Saturdays and Sundays, use business days — bear in mind it counts both endpoints, so over an identical range it reports one more total day than this tool. To turn a date into its ISO week label, use week number.