Date Difference Calculator

How to use the date difference calculator

Put a start date in the first box and an end date in the second, and the tool reports the gap between them straight away. Both fields are native date inputs, so you can type the numbers or use your device’s calendar picker, whichever is quicker. The example already loaded, 1 January to 25 December 2026, shows the tool working before you touch anything.

The order you enter them in does not matter: the calculator sorts the pair before it counts, so an end date that sits before the start date gives the same answer rather than a negative number or a zero.

That means you can paste two dates out of an email in whatever order they appeared and still get the right gap, which is worth more than it sounds when the dates arrived as "from the 3rd, until the 28th of last month".

The headline number is total days, and it counts the start date but not the end date — the span runs from the start date up to, but not including, the end date. That is how notice periods, rental nights, contract windows, and shipping estimates are normally quoted, and it is why a Monday-to-Tuesday booking is one night rather than two.

When you want both endpoints included — "how many days am I off, counting my first day and my last day?" — add one to the total yourself.

Underneath the total sit the same span described other ways. The calendar breakdown gives you years, months, and days, which answers a genuinely different question from the raw day count: it follows the calendar, so its months are real months of unequal length rather than blocks of thirty days. That is also why the breakdown will never divide neatly out of the day count.

Adding one month to 31 January has no correct answer, only a stated convention, and this tool clamps the anniversary to the last day that exists — 28 February, or 29 February in a leap year. Weeks and whole months are shown alongside for when a project plan, a lease, or an invoice is measured in those units instead.

Whatever you change, the address bar updates to match, so copying the URL hands someone else the exact same two dates and the exact same answer.

What about weekends and public holidays?

The last two lines split the span by day of week. Working days counts every Monday through Friday inside the window, and weekend days counts every Saturday and Sunday; together they always add back up to the total, which makes them a useful check that you entered the dates you meant.

Public holidays are not deducted, and that is deliberate rather than an oversight: the United States has 11 federal holidays set by 5 U.S.C. 6103, England and Wales run a different list published at gov.uk, Scotland and Northern Ireland differ again, and private employers in most countries are free to observe whichever they choose.

The formula, worked line by line

The total is an exact day count, not an estimate. Both dates are converted to UTC midnights before subtracting, so a daylight-saving transition in the middle of the span — an hour lost in spring, an hour gained in autumn — cannot round the answer up or down a day the way a local-time subtraction can.

Every day in the subtraction is exactly 86,400,000 milliseconds long, because a civil date has no time zone attached to it in the first place.

The calendar breakdown is a separate calculation running on the same two dates, and it deliberately does not derive from the day count. Whole months are counted on the calendar first, the monthly anniversary is clamped into whatever month it lands in, and only the remainder is measured in days. Trying to reverse the process — dividing 358 days by 30 or by 365.25 — gives 11.9 months or 0.98 years, neither of which is the answer anyone means.

total days = (end at UTC midnight − start at UTC midnight) ÷ 86,400,000 ms
             counts the start date, excludes the end date
whole months = calendar months from the start date, minus 1 if that month’s anniversary has not arrived
days = day count from that clamped anniversary date to the end date

Leap years are handled by simply counting the days that exist, with no separate setting and no approximation. The effect is easy to see: the same 1 January to 25 December span is 358 days in 2026 but 359 days in 2028, because 29 February 2028 falls inside the window.

Run the span from 1 January 2026 to 1 January 2028 and you get exactly 730 days, which is 365 + 365, since neither 2026 nor 2027 is a leap year.

Why 31 January to 1 March is one month and one day

The anchored-anniversary method is what keeps the years, months, and days breakdown honest at awkward month ends. Counting whole months first and then measuring the remaining days from the clamped anniversary means 31 January to 1 March comes out as one month and one day, instead of the negative day count you get from borrowing February’s 28 days.

It also settles a real ambiguity rather than pretending there is not one: there is no universally correct value for "31 January plus one month", so the tool states its convention — clamp to the last day of the target month — and applies it everywhere. If a contract of yours defines month-end rollover differently, the day count is the figure to lean on, because it has no convention baked into it beyond the endpoint rule.

Questions people ask