Date Calculator
Add or subtract years, months, weeks and days from any date, or measure the gap between two dates in years, months, days, weeks, hours and business days.
Pick a date to get started
How to use this calculator
Add / subtract
- Pick a start date — type it straight into the field or open the calendar with the button beside it. It starts on today.
- Choose whether you are adding time or subtracting it.
- Fill in any combination of years, months, weeks and days. Blank fields count as zero.
- The result shows the weekday, the full date, the ISO form for pasting elsewhere, and how many days you have moved.
Difference
- Choose the two dates. Order does not matter — the gap is the same either way.
- Turn on Include the end date if the last day should count as one of the days.
- Turn on Count business days only to headline the Monday-to-Friday figure instead of the raw day count.
- Read the calendar breakdown in years, months and days, plus totals in days, weeks and hours.
How the maths works
Days, weeks and hours are straightforward, because those units never change length:
total days = (end date − start date) in days
total weeks = total days ÷ 7
total hours = total days × 24
Months and years are the awkward part, because a month can be 28, 29, 30 or 31 days long. A calendar difference is therefore worked out by counting whole months first:
- Take the largest number of whole months that still lands on or before the end date.
- Split that into years and months.
- Count the leftover days from there to the end date.
This is why 31 January to 1 March comes out as one month and one day: one month lands on 28 February, and there is a single day left over.
Business days are counted from whole weeks — each full week contributes five — with the remaining few days checked individually. Saturdays and Sundays are excluded; public holidays are not.
Worked examples
A 90-day deadline
A contract signed on 15 March 2026 must be renewed within 90 days.
- March has 31 days, so 16 days take you to 31 March
- April (30) and May (31) use 61 more, reaching 77 days on 31 May
- 13 days into June gives the deadline: Saturday, 13 June 2026
A month after the end of the month
One month after 31 January 2024.
- February 2024 has 29 days, because 2024 is a leap year
- There is no 31 February, so the day clamps to the end of the month
- Result: Thursday, 29 February 2024
- The same sum in 2023 gives 28 February instead
Working days in a two-week sprint
From Monday 5 May 2025 toFriday 16 May 2025, including the end date.
- Total days including both ends: 12
- One weekend falls inside the range, removing 2 days
- Business days: 10
Frequently asked questions
Properly. A year is a leap year if it divides by 4, except century years, which must divide by 400 — so 2024 and 2000 are leap years, while 1900 and 2100 are not.
That means a stretch from 1 January 2024 to 1 January 2025 counts as 366 days, while the same span a year later counts 365.
The day is moved back to the last day of that month. One month after 31 January is 28 February in a normal year and 29 February in a leap year, because there is no 31 February.
The result card tells you when this clamping has happened so the answer is never silently surprising.
Because month lengths vary. This calculator applies years and months first, clamps the day if needed, and only then adds the weeks and days — the order almost every calendar application uses.
So 31 January plus one month and one day is 1 March: first to 28 February, then one day on.
It depends on what you are counting. A hotel stay from Monday to Friday is four nights but five days; a project running Monday to Friday is five working days.
Leave the switch off to count the gap between the dates, and turn it on when both the first and last day should count.
No. It excludes Saturdays and Sundays only, because public holidays differ by country, state and even by employer.
If your deadline depends on holidays, count them up for your own calendar and subtract them from the business day figure.
No. Dates are treated as whole calendar days rather than moments in time, so a clock change never turns a day into 23 or 25 hours in the arithmetic.
The total hours figure is simply the number of days multiplied by 24.