Date Difference Calculator

Q: Why is the answer in years and months different from the answer in days?

Because months are not a fixed length. Expressing a gap as years, months and days walks the calendar forward — one year, then one month, then the leftover days — and the size of each step depends on where you start. From 31 January, adding one month lands on 28 February, which is 28 days; from 31 March it is 30. The total-in-days figure has no such ambiguity because it just counts. Both are correct answers to slightly different questions, so the tool shows them side by side rather than picking one.

Q: Are both the start and end dates included?

By default the difference is exclusive: from Monday to Tuesday is one day, not two. That matches how durations normally work and how most date libraries behave. Some contexts genuinely want the inclusive count — billing a hotel stay, counting notice periods, or anything where both endpoints are days you are being charged for — so there is a switch for it. Getting this wrong is a classic off-by-one, which is why the tool states which convention it is using rather than leaving you to infer it.

Q: How are business days counted?

Monday to Friday inclusive, excluding Saturday and Sunday, and not accounting for public holidays. Holidays vary by country, region and sometimes by employer, so any figure that claimed to include them would be wrong for most visitors. If your calculation depends on holidays you will need to subtract them yourself against the calendar that actually applies. The weekday count on its own is still the right starting point for most delivery estimates and contractual notice periods.

Q: Does it handle leap years?

Yes, and it has to — a range spanning 29 February is a full day longer than the same range a year earlier. The calculation works on real calendar dates rather than assuming 365-day years, so any leap days in the range are counted automatically. The tool also tells you how many leap days fell inside the range, because that is often the explanation when a duration does not match the number someone expected from multiplying years by 365.

Q: Why might this disagree with a spreadsheet?

Two usual reasons. Spreadsheets often default to an inclusive count for date differences in some functions and exclusive in others, so check which one you used. And some spreadsheet date systems carry a deliberate bug for compatibility — the 1900 date system treats 1900 as a leap year, which it was not, so any range crossing February 1900 is a day out. For modern dates the two should agree once the inclusive setting matches.

Q: Can I work out a date rather than a difference?

Yes — switch to the add or subtract mode, give it a starting date and a number of days, weeks, months or years, and it returns the resulting date. That is the operation behind deadlines, renewal dates and notice periods. Adding months follows the usual convention of clamping to the end of the month, so one month after 31 January is 28 February rather than spilling into March, which is what most systems and contracts assume.

Work out the gap between two dates in years, months, days, hours and business days — or add a duration to a date to find a deadline.

Start date

End date

Count both the start and end dates

All calculations run in your browser against the real calendar, including leap years. Nothing you enter is uploaded.

What It Does

Give it two dates and it tells you how far apart they are, expressed several ways at once, because there is no single correct unit. The calendar breakdown walks forward in years, then months, then days, which is how a person describes an age or a tenure. The totals count the same gap in each unit on its own, which is what you want for a deadline or a billing period. The business-day figure excludes weekends, which is what contracts and delivery estimates actually run on. Leap days inside the range are counted properly and reported, since they are the usual reason a duration does not match what someone got by multiplying years by 365. There is also a second mode that runs the calculation the other way: give it a date and a duration and it returns the resulting date.

When to Use It

A contract specifies a notice period in business days and you need the actual date it expires.
You are calculating someone's exact age or length of service in years, months and days for a form that demands all three.
A project needs a deadline set a specific number of weeks out and you want the date rather than counting squares on a calendar.
You are reconciling a billing period and need to know whether the count should include both endpoints.
A duration in your data looks wrong and you want to check whether a leap day explains the discrepancy.

Worked Examples

2026-01-31 to 2026-02-28

The month-length trap. This is exactly 28 days, and also exactly one month by the clamping convention — from 31 January there is no 31 February, so one month lands on the 28th.

2024-02-01 to 2024-03-01

A range spanning a leap day. It is 29 days rather than the 28 the same range would be in a non-leap year, which the tool flags so the extra day is not a mystery.

2026-08-10 to 2026-08-24

Two weeks apart, but only ten business days. The gap between the calendar figure and the working figure is what most delivery and notice-period disputes come down to.

Features

Difference in years

months and days together

Totals in days

weeks

hours and minutes

Business day count excluding weekends

Inclusive or exclusive endpoint counting

Leap days in the range counted and reported

Add or subtract a duration to find a date

Month arithmetic clamped to the end of the month

Weekday of each date shown

Instant recalculation as you type

Runs entirely in your browser

How to Use

1. Enter a start date and an end date. 2. The breakdown appears immediately in calendar units and in totals. 3. Toggle inclusive counting if both endpoints should count. 4. Switch to add or subtract mode to work out a date from a duration instead. 5. Read the business-day figure if weekends should not count.

Common Mistakes

Assuming a month is 30 days. Adding 30 days to a date and calling it a month drifts by a day or two every time, and the error compounds across a schedule.
Getting the inclusive count wrong. Monday to Tuesday is one day as a duration but two days as a stay, and picking the wrong convention is the most common off-by-one in date work.
Multiplying years by 365. Any range containing a leap day is longer than that, and over a decade the error is more than two days.
Treating business days as calendar days times five sevenths. That approximation drifts depending on which weekday you start from, and it ignores that a range can begin or end on a weekend.
Expecting weekday counts to account for public holidays. They vary by country and employer, so a general tool cannot include them and any that claims to is wrong somewhere.

Frequently Asked Questions

Why is the answer in years and months different from the answer in days?

Are both the start and end dates included?

How are business days counted?

Does it handle leap years?

Why might this disagree with a spreadsheet?

Can I work out a date rather than a difference?