Date Calculator — Add or Subtract Days, Weeks, Months
Direction
—
—
Resulting date
0
days from start
—
weekday
0
day of the year
0
ISO week number
- Days left in that year
- 0
- Leap year
- No
- Weekend days skipped
- 0
Pick a start date, type how far you want to move, and the exact calendar date appears straight away — forwards or backwards. Days, weeks, months, and years can be combined in one go, and a checkbox switches the count to business days only, skipping Saturdays and Sundays. Everything runs in your browser.
How it works
- 1 Set the start date The field opens on today's date. Change it to any date between year 1 and 9999, or press 'Today' to jump back to the current date.
- 2 Choose add or subtract 'Add' moves forward in the calendar, 'Subtract' moves back. The direction applies to all four fields at once, so you don't need to type minus signs.
- 3 Enter the offset Fill in any combination of years, months, weeks, and days. Years and months are applied first as calendar steps, then the week and day count on top.
- 4 Read the result You get the full date with its weekday, the ISO form for copying into a spreadsheet, the signed day distance from the start, the day of the year, and the ISO week number.
Your data stays private
All processing happens entirely in your browser. No files, text, or data are ever sent to our servers. You can disconnect from the internet and this tool will still work.
Frequently asked questions
- What date is 90 days from today?
- Leave the start date on today, put 90 in the days field with 'Add' selected, and the answer appears instantly — along with the weekday, which is usually the part people actually need. Ninety days is almost never exactly three months: from 1 January it lands on 1 April, but from 1 March it lands on 30 May.
- What happens when the target month is too short?
- The day is clamped to the last day of that month. 31 January plus one month gives 28 February, or 29 February in a leap year — never 3 March. This is the same convention Excel's EDATE and Google Sheets use, so the result matches what a spreadsheet would give you.
- Why do years and months get applied before days?
- Because the order changes the answer. Starting from 30 January, one month then one day gives 1 March (28 February, then forward a day), while one day then one month gives 2 March. This calculator always applies years, then months, then weeks and days, and says so — a fixed order is the only way the result stays reproducible.
- How does the business days option work?
- With it ticked, the week and day fields are counted in weekdays: Saturdays and Sundays are stepped over and don't consume part of the count, and a week is treated as five business days. If the start date itself falls on a weekend, it first moves to the nearest weekday in the direction you're going. Years and months stay calendar-based. The counter shows how many weekend days were skipped.
- Are public holidays excluded?
- No. Holidays differ by country, region, and year — Germany alone has nine different sets of state holidays — so a built-in list would be wrong for most visitors. Business-day results count Monday to Friday only, which makes them an upper bound: subtract your own holidays from the total.
- Does the calculator handle leap years and leap days?
- Yes. Real calendar dates are used, so 29 February exists in 2028 and doesn't in 2027. The result card also tells you whether the date lands in a leap year, which matters if you are then counting a 365-day term from it.
- Is my data sent anywhere?
- No. The date arithmetic runs locally in JavaScript. Nothing is uploaded, logged, or stored — you can disconnect from the network and the tool still works.
From the blog
90 Days From Today: Getting Date Math Right Why 90 days isn't three months, what happens to 31 January plus one month, and how business-day counting differs from calendar counting. Read the post →Related tools
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