Date Difference Calculator
Free date difference calculator. Find the exact number of days, weeks, months and years between any two dates, including or excluding the end date.
Enter valid dates in the correct order.
Counting days between two dates by hand goes wrong quickly, because months vary in length and leap years add a day that is easy to forget. This calculator gives the exact interval in days, weeks, months and years, and lets you choose whether the end date counts.
It is built for the situations where the count has consequences: contract notice periods, visa durations, project deadlines, statutory time limits and payroll cut-offs.
How to use the Date Difference Calculator
Pick a start date
Any date, past or future.
Pick an end date
The order does not matter — the calculator reports the absolute interval either way.
Decide whether to include the end date
Inclusive counting adds one day. Legal and contractual counting rules vary, so check which convention applies to you.
Read the breakdown
The result appears in total days, weeks, and as a years-months-days composition.
Inclusive versus exclusive counting
From 1 March to 10 March is nine days if you count the intervals between dates, and ten if you count the dates themselves. Both are correct; they answer different questions.
Use exclusive counting for durations — how long something lasts. Use inclusive counting when every calendar day is a countable unit, such as hotel nights, hire days or statutory periods that count the first day.
When a deadline is legally significant, read the governing document. Many contracts and court rules specify precisely whether the first day, the last day, or both are counted.
Why "months" is genuinely ambiguous
Days and weeks are fixed; months are not. From 31 January, one month later could reasonably be 28 February, 2 March, or 3 March depending on the convention used.
The common approach — and the one used here — is to keep the same day number in the target month and clamp to the last day when it does not exist, so 31 January plus one month is 28 February (or 29 in a leap year).
Financial contracts often specify a 30/360 day-count convention instead, treating every month as 30 days and every year as 360. It is deliberately artificial, chosen because it makes interest arithmetic simple.
Business days versus calendar days
A calendar-day count includes weekends and holidays; a business-day count does not. Over a long period the difference is substantial — 90 calendar days is roughly 64 business days.
The eleven US federal holidays are New Year’s Day, Martin Luther King Jr. Day, Presidents’ Day, Memorial Day, Juneteenth, Independence Day, Labor Day, Columbus Day, Veterans Day, Thanksgiving and Christmas. Contracts frequently specify "business days" precisely because the count differs.
Leap years
A year is a leap year if it is divisible by 4, except century years, which must be divisible by 400. 2024 and 2000 qualify; 1900 and 2100 do not.
The rule exists because Earth’s orbit takes about 365.2422 days. Adding a day every four years overcorrects slightly, and the century exception removes the excess — leaving the Gregorian calendar accurate to within one day in roughly 3,200 years.
Where exact day counts matter
- Immigration — the US Substantial Presence Test and Schengen’s 90-days-in-180 rule both depend on exact day counts, and errors have real consequences.
- Employment — notice periods, probation end dates and statutory leave entitlements.
- Interest and penalties — daily-accrual products compute on exact days elapsed.
- Legal deadlines — statutes of limitation and filing windows, where a single day can end a claim.
- Project planning — converting a deadline into working days available.
Frequently asked questions
How many days are between two dates?
Enter both dates above for an exact figure. The calculator uses real calendar arithmetic including every leap day, rather than an average year length.
Should I include the end date?
Use exclusive counting for durations and inclusive counting when each calendar day is itself a unit, such as hotel nights or hire days. Legal deadlines vary — check the governing document.
How many weeks are in a year?
52 weeks and one day in a common year, or 52 weeks and two days in a leap year — which is why a fixed date advances one weekday each year, and two after a leap year.
How do I count business days?
Subtract weekends and public holidays from the calendar-day total. As a rough guide, business days are about 71% of calendar days over long periods.
Why do month calculations differ between tools?
Because there is no single correct definition of "one month" when day numbers do not exist in the target month. This tool clamps to the last valid day; financial systems often use a 30-day convention instead.
Which years are leap years?
Those divisible by 4, except century years not divisible by 400. So 2024, 2028 and 2000 are leap years, while 1900 and 2100 are not.
Can I calculate a date in the future?
Yes — set the end date to any future date and the calculator reports the interval remaining.
Does it handle very old dates?
It uses the proleptic Gregorian calendar throughout. For dates before the Gregorian reform of 1582, historical records may use the Julian calendar, which diverges by several days.
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