Date Calculator
Days, weeks, months and business days between two dates, or add and subtract days, weeks, months or years from any date — leap years handled exactly.
Date Calculator: with the default inputs, result is 90 days.
Used in 'days between' mode. Defaults to 90 days out.
Used in 'add or subtract' mode.
- Days
- 90
- Weeks and days
- 12 weeks, 6 days
- Months and days
- 2 months, 29 days
- Business days (Mon–Fri)
Weekdays only; public holidays are not excluded.
- 65
- Weekend days
- 25
- Day of the week
- Saturday → Friday
Assumptions
- Dates are local calendar dates; times and time zones are ignored.
- Business days are Monday–Friday with no holiday exclusions.
- Adding months keeps the day of month, clamped to the target month's length.
| After | Date | Falls on a |
|---|---|---|
| 7 days | October 17, 2026 | Saturday |
| 14 days | October 24, 2026 | Saturday |
| 21 days | October 31, 2026 | Saturday |
| 30 days | November 9, 2026 | Monday |
| 45 days | November 24, 2026 | Tuesday |
| 60 days | December 9, 2026 | Wednesday |
| 90 days | January 8, 2027 | Friday |
| 120 days | February 7, 2027 | Sunday |
| 180 days | April 8, 2027 | Thursday |
| 365 days | October 10, 2027 | Sunday |
Calendar days counted from the start date, the day itself not counted. Deadlines written as 'within 90 days' are calendar days unless the contract or court rule says business days.
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Date Calculator by CalculateItNow
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How this is worked out
The formula
days between = day number(end) − day number(start) (+1 if the end date is included) weeks = days ÷ 7, remainder in days months = whole calendar months, then leftover days business days = days − Saturdays − Sundays in the range add N days = start + N calendar days; add N months keeps the day of month (clamped to the month's length)
Open How it’s calculated above to see this worked through with your own numbers.
What you enter
- What do you want to do?
- Choose one of 2 options.Days between two dates · Add to or subtract from a date
- Start date
- A calendar date.defaults to today
- End date
- Used in 'days between' mode. Defaults to 90 days out.defaults to today+90
- Amount to add
- Used in 'add or subtract' mode.from 0 to 100000 · whole numbers only · defaults to 90
- Unit
- Choose one of 4 options.Days · Weeks · Months · Years
- Subtract instead of add
- Turn this on or off.defaults to off
- Include the end date(under More options)
- Counts both the start and end day (adds 1). Useful for rental periods and medication courses.defaults to off
What you get back
- Resultmain answer
- Days
- Weeks and days
- Months and days
- Business days (Mon–Fri)
- Weekdays only; public holidays are not excluded.
- Weekend days
- Resulting date
- Day of the week
What this assumes
- Dates are local calendar dates; times and time zones are ignored.
- Business days are Monday–Friday with no holiday exclusions.
- Adding months keeps the day of month, clamped to the target month's length.
About this calculator
Two jobs in one tool. Days between two dates counts the calendar days, weeks, whole months and business days from one date to another. Add or subtract finds the date a given number of days, weeks, months or years before or after a start date — the fast way to answer "what's 90 days from today?" or "when does a 6-week course end?"
Counting between two dates
The count is the number of midnights crossed. From Friday to Monday is 3 days; from 1 January to 31 December is 364 days (365 in a leap year), because the first day itself isn't counted. If you want both ends included — a hotel stay, a prescription, a notice period expressed as "days" — turn on Include the end date under More options, which adds one.
Weeks are days ÷ 7 with the remainder shown. Months are whole calendar months from the start day, with leftover days after that; the day of month is kept where possible, so 31 January to 28 February is "1 month, 0 days" in a common year.
Business days are Mondays through Fridays in the range. Public holidays are not removed — they vary by country and employer — so subtract any that fall in your window.
Adding to a date
Days and weeks are exact. Months and years keep the same day of the month, so 15 March plus 3 months is 15 June. When that day doesn't exist (31 January plus 1 month), the result is clamped to the last day of the target month, and the calculator tells you so. That's the convention used by banks, most spreadsheet software and the ISO 8601 standard.
Deadlines given in days ("within 90 days") are usually calendar days unless the contract or court rule says business days. Check the wording; for legal deadlines the counting rules (whether day one is the trigger date) also matter.
Leap years and DST
All arithmetic is done on calendar dates, so leap days are counted and clock changes for daylight saving never produce 23- or 25-hour "days". A year is a leap year if it's divisible by 4, except century years, which must be divisible by 400 — 2000 was, 2100 won't be.
Frequently asked questions
▸What date is 90 days from today?
Choose 'Add to or subtract from a date', leave the start as today, and enter 90 days. The result shows the date and its day of the week. 90 days is about 12 weeks and 6 days — not exactly 3 months.
▸How do I count the days between two dates?
Subtract the earlier date's day number from the later one's. The calculator does this on calendar dates so leap days are included and daylight-saving changes don't matter. Add 1 if you want to count both the first and last day.
▸How many business days are between two dates?
Count the calendar days, then subtract the Saturdays and Sundays that fall in the range. The calculator does this exactly but does not remove public holidays.
▸What happens when I add a month to January 31?
There's no February 31, so the result is the last day of February (28 or 29). Adding another month from there gives March 28 or 29, not March 31 — a known quirk of month arithmetic.
▸Is a year 365 or 365.25 days?
A calendar year is 365 days, or 366 in a leap year. The average over the 400-year Gregorian cycle is 365.2425 days. This calculator uses actual calendar years, so adding one year to 1 March 2027 gives 1 March 2028 regardless of the leap day in between.
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