Add days to a date

Add or subtract any number of days (or weeks, months and years) and get the date and weekday it lands on, with each step printed.

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Days are exact, months are elastic

Adding days is plain counting: the calculator converts the date to a day number, adds, and converts back. Months and years are different because they vary in length. The rule used here (and by ISO 8601 libraries such as JavaScript Temporal, Java's java.time and Excel's EDATE) is: move to the same day number in the target month, and if that day doesn't exist, use the last day of that month.

Month-end clamping, one month at a time

Pick a day in January 2027, then step forward. The left column always counts from the original date; the right column adds one month to the previous result, the way a naive loop or a chain of spreadsheet formulas does.

Months added: 0
+ monthsFrom the startChained
0Sun 31 Jan 2027Sun 31 Jan 2027

Press "+1 month" a few times to watch February squeeze the date.

Mixed amounts are applied in a fixed order

When you add years, months, weeks and days together, years and months are applied first (with at most one clamp), then weeks and days. Order matters: 30 January 2027 + 1 month + 1 day is 1 March (30 Jan → 28 Feb → 1 Mar), whereas adding the day first would give 31 Jan → 28 Feb. The tape shows the intermediate date so the result can be checked by hand.

Quick reference from a start date

Need the answer from today rather than a chosen date? The days from today pages list the common spans (30, 60, 90, 180 days) with the dates they fall on. For deadlines that skip weekends, add business days instead; for terms written in months, use add months to a date.

Questions people ask

How do I add days to a date?
Enter the start date and the number of days. The start date is day zero, so Monday + 1 day is Tuesday and 1 March + 30 days is 31 March. To go backwards, choose Subtract.
What is 31 January plus one month?
28 February, or 29 February in a leap year. There is no 31 February, so the day is clamped to the last day of the month. Adding days instead avoids that ambiguity: 31 January + 30 days is always 2 March in a common year.
Is adding 4 weeks the same as adding 1 month?
No. 4 weeks is exactly 28 days, while a month is 28 to 31 days depending on the month. From 10 March, 4 weeks is 7 April but 1 month is 10 April.
How do I subtract days from a date in Excel?
Dates in Excel and Google Sheets are day numbers, so =A1-30 gives the date 30 days before A1. For months, use =EDATE(A1,-3), which clamps month ends the same way this calculator does.
What happens when I add a year to 29 February?
It becomes 28 February of the next year, because the target year has no 29 February. Some legal systems treat a leap-day anniversary as 1 March instead; the age calculator lets you choose.

Other date calculators

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