How to use the Add or Subtract Days from a Date
- Choose the start date. It starts as today.
- Choose whether to add days or subtract days.
- Enter the number of days.
- Read the resulting date and the day of the week.
Formula used
Result date = start date ± number of days, counted on the calendar including leap years.
Worked example
Here is the Add or Subtract Days from a Date worked through with the example values shown above, so you can check each step by hand.
| Inputs | |
|---|---|
| Operation | Add days |
| Number of days | 90 days |
| Result | |
| Resulting date | 28 January 2027 |
| Day of the week | Thursday |
| That is | 12 weeks and 6 days |
Worked example
Starting on 30 October 2026 and adding 90 days gives 28 January 2027, which is a Thursday. The 90 days are 12 weeks and 6 days, and because 12 whole weeks do not change the day of the week, only the 6 extra days do. Friday plus 6 days is Thursday.
Subtracting works the same way. Going back 30 days from 30 October 2026 lands on 30 September 2026, a Wednesday.
How the date is worked out
The calculator converts the start date into a count of days since a fixed reference point, adds or subtracts your number, and converts it back to a calendar date. This means month lengths and leap years are handled correctly without any rule of thumb.
For example, adding 1 day to 28 February 2028 gives 29 February 2028, because 2028 is a leap year. Adding 1 day to 28 February 2027 would give 1 March 2027.
Typical uses
People use this for return and refund windows, notice periods, warranty expiry, payment terms such as net 30 or net 45, medicine courses, project milestones and pregnancy due dates counted in days. Getting the date right matters when a missed deadline has a penalty.
Always check how the rule counts. A “30-day notice” given on 1 June may be counted from 1 June or from 2 June, and the end date will differ by one day.
Weekends and holidays
The tool counts every calendar day, including weekends and public holidays. If a deadline falls on a Sunday or a holiday, many offices and banks move it to the next working day, but this varies between institutions and between types of deadline.
If your period is in working days, count only Monday to Friday and skip official holidays. This calculator does not do that automatically.
Days, weeks and months are different
Adding 30 days is not the same as adding a month. In a non-leap year, 31 January plus 30 days is 2 March, because February has only 28 days, while one month after 31 January is usually treated as the end of February. When a contract says “within 30 days” or “one month”, check which counting is meant, and whether the first day counts.
Legal and business deadlines may also count working days instead of calendar days and skip weekends and public holidays, which this calculator does not do. For a deadline that matters, confirm the date against the rule that applies to you, and add a margin.
Frequently asked questions
Does the start date count as day one?
No. Adding 1 day to 1 January gives 2 January. The start date itself is day zero.
How many days are in 3 months?
It depends on which months. Three months can be 89 to 92 days. Use an exact date calculation instead of multiplying by 30.
Does it skip weekends?
No. Every calendar day is counted.
Can I subtract days from a date?
Yes. Choose Subtract days and enter the number.
Does it handle leap years?
Yes. The calendar is used directly, so 29 February is included when it exists.
What is the largest number of days I can enter?
The field accepts up to 1,00,000 days, which is more than 273 years.
Does this skip weekends or holidays?
No. It counts calendar days. Working-day deadlines need a business-day calculation that accounts for local holidays.
This calculator gives estimates for information only. Actual figures from a bank, employer, tax authority or doctor may differ. It is not financial, tax, legal or medical advice.