Days Between Dates Calculator

Find the number of days between two dates, plus weeks and total months estimate.

Start Month

Start Day

Start Year

End Month

End Day

End Year

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Enter your values and click Calculate

How It Works

Both dates are converted to UTC midnight timestamps using Date.UTC() with a round-trip validity check that catches impossible dates like February 30. The difference in milliseconds is divided by 86,400,000 and rounded to produce an exact whole-day count. Approximate weeks are computed as days ÷ 7; approximate months use an average of 30.4375 days per month (365.25 ÷ 12); approximate years use 365.25 days. The direction note is determined by the sign of the raw difference before the absolute value is taken. Because all arithmetic happens in UTC, daylight saving time transitions — which shift local midnight by an hour — cannot cause off-by-one errors.

Examples

Project timeline

From March 1, 2026 to April 1, 2026.

Result: 31 days between the dates.

Counting days to a trip

From January 10, 2026 to February 5, 2026.

Result: 26 days between the dates.

Annual contract duration

From June 15, 2025 to June 15, 2026.

Result: 365 days (approximately 52.14 weeks, 11.99 months, 1.0 year).

Frequently Asked Questions

Does this include the start date?

The result is the difference between the two dates, so the start date itself is not counted. If you want an inclusive count — for example, to count days on a project including the first day — add 1 to the result.

Why use UTC?

UTC avoids daylight saving time changes that shift local midnight by one hour, which would otherwise cause an off-by-one error on the days the clocks change. UTC midnight is always exactly 86,400,000 ms apart.

Are months and years exact?

Months and years shown are approximations based on average day counts. The exact primary result is always the whole-day count, which is precise regardless of varying month lengths or leap years.