Add Days to a Date
Choose a start date, a direction, an amount and a unit — days, weeks, months or years — to get the resulting date and its weekday. Use it to add to or subtract from a date, whether that's counting a number of days forward, adding weeks to a date, or working out what a contract's "90 days from today" actually means.
Quick reference: common offsets from today
| Offset | Date | Weekday |
|---|---|---|
| +30 days | 2026-11-07 | Saturday |
| +45 days | 2026-11-22 | Sunday |
| +60 days | 2026-12-07 | Monday |
| +90 days | 2027-01-06 | Wednesday |
| +180 days | 2027-04-06 | Tuesday |
| +365 days | 2027-10-08 | Friday |
How adding and subtracting dates works
Adding to or subtracting from a date means moving a fixed number of days, weeks, months or years away from a starting point to land on a new date. Days and weeks are the simplest case: a day is always 24 hours on the calendar and a week is always exactly 7 of them, so "add 42 days" and "add 6 weeks" always produce the identical result — there's never any ambiguity or rounding. Starting from Wednesday, September 23, 2026, adding 90 days lands on Tuesday, December 22, 2026; adding 6 weeks (42 days) lands on Wednesday, November 4, 2026; and subtracting 45 days lands on Sunday, August 9, 2026. Each of those is a plain count of calendar days, and the tool above will reproduce them instantly if you plug in that start date.
Months and years are different, because calendar months don't all have the same number of days. Adding "1 month" to a date really means "land on the same day number, one month later" — which breaks down when the starting day doesn't exist in the target month. Saturday, January 31, 2026 plus one month can't become "February 31", since February only has 28 days that year, so the result clamps down to Saturday, February 28, 2026 rather than rolling forward into March. The same clamping rule applies whenever the target month is shorter than the one you started in: Sunday, May 31, 2026 plus one month clamps to Tuesday, June 30, 2026, since June has only 30 days. It isn't limited to February, and it isn't a bug — it's the same convention banks, courts and billing systems use for "one month from now" on a 31st. Leap years shift the February case only: Wednesday, January 31, 2024 plus one month lands on Thursday, February 29, 2024, since 2024 is a leap year and February has 29 days to clamp to instead of 28. Years work the same way in miniature — the one edge case is a February 29 birthday, which clamps to February 28 in any non-leap target year.
Because of that clamping behavior, adding months or years isn't always reversible day-for-day: adding one month to January 31 gives February 28, but subtracting one month from February 28 gives January 28, not January 31. If a calculation needs to be exactly reversible, days or weeks are the safer unit; months and years are the right choice when what you actually mean is "the same date, N calendar months later," such as a monthly billing cycle or a lease renewal. Already have two dates and want the span between them instead of computing a single result date? The days between two dates calculator runs the reverse direction, turning a start and end date into a day, week, month and year count.
Frequently Asked Questions
How do I calculate a date 90 days from today?
Set the start date to today, choose "Add," enter 90, and pick "Days" as the unit. The result date, its weekday, and the total calendar days moved are shown immediately. The table below already has +90 (and five other common offsets) worked out from today.
What happens when adding a month lands on a day that doesn't exist?
It clamps to the last real day of that month. Jan 31 plus one month is Feb 28 in a non-leap year (Feb 29 in a leap year) — not Mar 2 or Mar 3, which is what you'd get if the extra days simply rolled over.
Can I subtract instead of add?
Yes — switch the direction to "Subtract" and the same logic runs backward: 45 days before a date, or 6 months before it, with the same month-end clamping rules.
Does this give me the weekday of the result?
Yes, shown under the result date. Deadlines that land on a weekend often get moved to the next business day — that's what the business days calculator handles separately.
What date is 6 weeks from now?
Pick today as the start date, set the unit to "Weeks," and enter 6 — or just enter 42 with the unit set to "Days," since a week is always exactly 7 days and never clamps. Both give the identical result date and weekday.
How do I add weeks to a date instead of days?
Switch the unit dropdown to "Weeks." Each unit multiplies the amount you enter by 7 days before adding, so "3 weeks" and "21 days" always land on the same result — weeks are just a shorthand for a day count, unlike months, which vary in length.