Date Calculator
Date duration calculator: count the days, weeks, months and years between two dates, or add and subtract days and business days from today or any date.
Every convention this page applies is named in the result rather than assumed. Your numbers stay in this browser.
Results
How to read this: the verdict describes how much room your numbers leave, not a decision or an offer. Change any input to see how much the result moves.
Assumptions and formula
Every date is a whole calendar day, handled in UTC so no clock change can shorten one. The difference mode finds whole years and months by stepping forward from the earlier date with end-of-month clamping, then counts the days left over; total days counts the nights between the two dates, plus one when you choose to count the last day. The add and subtract modes apply years and months first, then weeks and days, then business days.
Adding a month to the 31st lands on the last day of the next month, because that month has no 31st; the result says when that happened. Business days are Monday to Friday, with no public holidays skipped. The proleptic Gregorian calendar is used throughout.
Worked example
From Monday 4 March 2024 to Friday 8 March 2024 is 4 days counting the nights between, or 5 counting both days; all of them are weekdays. From 15 January 2023 to 20 March 2024 is 1 year, 2 months and 5 days, 430 days in all. Ten business days after Friday 8 March 2024 is Friday 22 March.
Frequently asked questions
How do I work out a date a certain number of days from today?
Add the days to today’s date, counting each calendar day including weekends. Ninety days from 1 January is 1 April in a normal year and 31 March in a leap year, because February adds a day. If the period is in business days, weekends are skipped and the answer lands later; a 30-business-day deadline from a Monday is six weeks away, not four and a bit. Enter the start date, the number of days and whether they are calendar or business days, and this calculator returns the exact date with the day of the week.
Is the last day counted when working out days between two dates?
It depends on what you are measuring, and this page lets you choose. Counting the nights between — Monday to Friday is 4 — suits deadlines, ages and durations. Counting both ends — Monday to Friday is 5 — suits leave, hotel stays and "day 1 to day N" schedules. Most calculators pick one silently; the result here says which convention it used.
What is 31 January plus one month?
28 February in an ordinary year, 29 in a leap year. February has no 31st, so the day is held to the last day of the month. The same happens for 31 March plus one month (30 April) and 29 February plus one year (28 February). This page reports when that adjustment happened, because it changes the answer to questions like "when does my 30-day notice end".
How are business days counted?
Monday to Friday, skipping Saturdays and Sundays. Ten business days from a Friday is the Friday two weeks later. Public holidays are not skipped, because they differ by country and region; if one falls inside the span, add a day yourself. The difference mode also reports how many of the days between two dates are weekdays.
Why does the number of months between two dates depend on the direction?
Because calendar months are uneven. Stepping forward from 31 January reaches 28 February after one month, but stepping back from 28 February reaches 28 January. This page always steps forward from the earlier date, whichever order you entered them in, and says so when it swaps them.
Does this account for time zones or daylight saving?
No, deliberately. A date calculator works in whole days: 10 March to 11 March is one day whether or not the clocks changed overnight. For spans between two clock times, across time zones, or where the 23-hour day matters, use the time calculator instead.
How many days until a date, and does the count include weekends?
A days calculator counts every calendar day, weekends included, so 30 days from a Monday is a Wednesday four weeks and two days later. A business days calculator skips Saturdays and Sundays, so 30 business days from the same Monday lands six weeks later. This page does both: the days between dates calculator counts the gap in either mode and says whether the last day is included, and the date difference calculator view breaks the same gap into years, months and days for anniversaries and notice periods.
How do I add days to a date, including business days?
Enter the start date and the number of days, and choose calendar or business days. An add days to date calculator in calendar mode counts every day, so 45 days from 10 January is 24 February. In business-day mode weekends are skipped, so 45 business days from a Friday lands nine weeks later, on a Friday. Month arithmetic is separate: adding one month to 31 January gives 28 or 29 February, and this page states which end-of-month rule it applied.