How to add or subtract days from a date
Choose a start date, pick add or subtract, and enter any mix of years, months, weeks and days. The result updates as you type. Leave the fields you don't need at zero.
The calculator applies years and months first, on the calendar, then adds weeks and days. This matters at the end of a month: one month after 31 January is 28 February (29 in a leap year), because February has no 31st. Adding 30 days instead would land on 2 March.
Worked example: 90 days after 15 January 2026 is Wednesday, 15 April 2026. Adding 3 months instead also lands on 15 April, but that's only a coincidence of this start date: 3 months after 30 November is 28 February (90 days), while 3 months after 15 May is 15 August (92 days).
Popular date calculations
| Question | What to enter |
|---|---|
| What is the date 30 days from today? | Today + 30 days |
| 90-day return or warranty window | Purchase date + 90 days |
| Six-month review or probation end | Start date + 6 months |
| Due date of a pregnancy (Naegele's rule) | First day of last period + 280 days |
| When was 100 days ago? | Today − 100 days |
| Notice period of 4 weeks | Notice date + 4 weeks |
Days vs. months vs. business days
"30 days" and "1 month" are not the same: depending on the month, one month is 28 to 31 days. Many contracts, return policies and government deadlines are written in calendar days, while banks, couriers and courts often count business days that skip weekends and public holidays. For those, use the business days calculator.
A pregnancy due date estimated with Naegele's rule is only an estimate: few babies arrive on the exact day, and your doctor or midwife may adjust it after an ultrasound scan.
Frequently asked questions
What is the date 90 days from today?
Set the start date to today, choose Add and enter 90 in Days. The result appears immediately, along with the day of the week. Ninety days is about three months, but usually one or two days less than three calendar months.
How do I subtract days from a date?
Choose Subtract (−) and enter the number of days, weeks, months or years to go back. For example, 15 April 2026 minus 90 days is 15 January 2026.
What is one month after 31 January?
28 February, or 29 February in a leap year. When the target month is shorter, the date moves to that month's last day rather than spilling into the next month.
Does the calculator count the start date?
No. Adding 1 day to Monday gives Tuesday. That's the usual meaning of "days after" in deadlines and due dates.
Results use the Gregorian calendar. Legal deadlines that fall on a weekend or holiday are often moved to the next working day; check the rules that apply.