How does the calculator work out the exact duration?

It compares the two datetimes calendar unit by calendar unit — minutes, hours, days, months and years — borrowing from the next-larger unit where needed (for example a negative day count borrows the real number of days from the previous month). This gives a true calendar duration like '2 years, 3 months, 14 days' rather than a flat day count, which is why the breakdown respects leap years and uneven month lengths.

What is the difference between the breakdown and the totals?

The breakdown splits the gap into years, months, days, hours and minutes. The totals re-express the same gap as a single unit each — total weeks, total days, total hours and total minutes — so you can answer questions like 'how many hours is that?' without doing the maths yourself.

How are business days counted?

The tool walks every calendar day from the start to the end and counts only Monday to Friday, skipping Saturday and Sunday. It does not subtract public holidays, because those vary by country and region — treat the business-day figure as working days excluding weekends only.

What does 'include the end day' do?

By default the duration is the gap between the two instants, so a Monday-to-Friday range is four days. Tick 'include the end day' to count both endpoints, which adds one day to the total — useful for things like hotel nights, project schedules or leave requests where both the first and last day count.

Can I add or subtract weeks, months and years at once?

Yes. In the add/subtract mode you can combine years, months, weeks, days, hours and minutes in a single calculation. Months and years are applied as calendar units first (with day-of-month clamped to the last valid day, so 31 Jan minus one month lands on the correct end of February), then weeks, days, hours and minutes are applied exactly.

Is my data sent anywhere?

No. Every calculation, your saved history and the CSV export all happen entirely inside your browser using JavaScript. Nothing is uploaded, logged or shared, so it is safe for confidential contract dates, medical timelines or anything else private.

Date Duration Calculator

The Date Duration Calculator answers two everyday questions precisely: how long is it between these two dates? and what date is it if I add or subtract this much time? It is built for contract terms, project timelines, notice periods, visa stays, pregnancy and milestone tracking, age gaps, billing cycles and any situation where an approximate “about three months” simply will not do. Unlike a quick day-count, it gives you a true calendar breakdown — years, months, days, hours and minutes — alongside running totals so you can read the same span any way you need it.

How it works

In “Time between two dates” mode you pick a start and end datetime. The tool compares them unit by unit and borrows from the next-larger unit wherever a value goes negative — so the day count borrows the real length of the previous month, which is what makes the result correct across leap years and uneven months. It then reports the gap as total months, total weeks, total days, total hours and total minutes, and counts the business days (Monday to Friday) in between. If you enter the end before the start, it shows the absolute duration and flags the inversion rather than erroring.

In “Add / subtract a duration” mode you choose a base date, a direction, and any combination of years, months, weeks, days, hours and minutes. Calendar units are applied first — with the day clamped to the last valid day of the destination month so month-end arithmetic behaves — then exact units are applied in milliseconds. You instantly see the resulting datetime, its day of the week, and how many days were shifted.

Every result can be copied to your clipboard or saved to a history list that survives page reloads via local storage, and the whole history exports to CSV with one click.

Example

Say a fixed-term contract runs from 1 March 2026 to 30 November 2026. The calculator reports 8 months, 29 days — roughly 39 weeks, 274 days, and about 195 business days excluding weekends. Switch to add/subtract mode, set the base to 30 November 2026, and subtract 3 months to confirm the notice deadline lands on 30 August 2026 (a Sunday). Tick “include the end day” when both the first and last day count, such as counting hotel nights or annual-leave days, and the total nudges up by one.

From	To	Calendar duration	Total days
1 Jan 2026	1 Jan 2027	1 year	365
1 Mar 2026	30 Nov 2026	8mo 29d	274
15 Jun 2026	15 Sep 2026	3 months	92

Every figure is computed in your browser — no dates are uploaded or stored on any server.