Date Difference Calculator

Count the days, weeks, months and business days between any two dates.

Draft — figures checked, awaiting an editorial read. Not indexed.

Formula: Days = |end − start| in whole UTC days. Business days = whole weeks × 5, plus the weekdays in the remainder.

What this calculates

This counts the gap between two dates in several units at once: raw days, weeks, whole calendar months, whole years, and business days. The business day count is the one people usually came for, since deadlines, notice periods and shipping estimates are all quoted in working days. It counts Monday to Friday and does not exclude public holidays, because those vary by country, state and industry — a national figure would be wrong for most readers rather than helpful to all of them.

How it works

Both dates are converted to a day number in UTC and subtracted, which sidesteps daylight saving entirely — a date difference should never change because a clock moved. Weeks are days divided by seven. Months are counted as real calendar months rather than days divided by thirty: the year difference times twelve, plus the month difference, minus one if the end day of month falls before the start day. Business days take the whole weeks in the span, multiply by five, then walk the leftover days individually and count only the weekdays.

Worked example

From 1 January 2026 to 25 December 2026: that is 358 days, or 51.14 weeks. Whole calendar months: (2026 − 2026) × 12 + (12 − 1) = 11, and since the end day (25) is after the start day (1), no adjustment applies — so 11 months. Business days: 358 ÷ 7 = 51 whole weeks giving 255, plus one leftover day which happens to be a weekday, for 256 business days.

Common mistakes

Estimating months as days divided by 30, which drifts by roughly five days a year. Second, ambiguity about whether the count is inclusive: this calculator returns the difference, so 1 January to 2 January is one day, not two. If you need to count both endpoints — as some notice periods do — add one. Third, treating business days as universal when your organisation, contract or country observes holidays this calculator knows nothing about.

Common questions

Does the business day count exclude public holidays?

No, it counts Monday to Friday only. Holidays differ by country and even by state or industry, so excluding a fixed set would be wrong for most people using the page.

Is the result inclusive of both dates?

No, it is the difference between them. 1 January to 2 January returns one day. Add one if your use case counts both endpoints.