How to add days to a date
- 1.
Pick the start date
Today is filled in by default - change it to any date you need.
- 2.
Choose add or subtract
Decide whether you want to go forward or back in time.
- 3.
Enter the period
Type the number of years, months, weeks and days, or use a quick pick such as 7, 30 or 90 days.
- 4.
Read the result
You get the resulting date, the day of the week, the ISO week number, the day of the year and whether it is a working day.
How adding days, months and years works
Days and weeks are added exactly - one week is always 7 days. Months and years are added by the calendar: 15 March plus 1 month is 15 April, no matter how many days March has. When the target month is shorter and the day does not exist, the calculator uses the last day of that month, so 31 January 2026 plus 1 month gives 28 February 2026. Years and months are applied first, then weeks and days.
Examples from 11 October 2026:
- + 30 days = 10 November 2026 (Tuesday),
- + 100 days = 19 January 2027,
- - 2 weeks = 27 September 2026,
- + 6 months = 11 April 2027.
The start day itself is not counted. Adding 1 day to 11 October gives 12 October, which is how most contracts, invoices and legal deadlines are counted.
Popular periods from 11 October 2026
| Period | Resulting date | Day of the week | Typical use |
|---|---|---|---|
| + 7 days | 18 Oct 2026 | Sunday | short payment term |
| + 14 days | 25 Oct 2026 | Sunday | EU 14-day right to cancel online purchases |
| + 30 days | 10 Nov 2026 | Tuesday | net 30 invoice, free trial |
| + 60 days | 10 Dec 2026 | Thursday | net 60 invoice |
| + 90 days | 9 Jan 2027 | Saturday | 90-day visa-free stay, probation period |
| + 180 days | 9 Apr 2027 | Friday | roughly half a year |
| + 365 days | 11 Oct 2027 | Monday | one year (2027 is not a leap year) |
Notice how many of these fall on a weekend. If a deadline lands on a Saturday, Sunday or public holiday, many rules move it to the next working day, so it is worth checking the "Type of day" box in the result.
Calendar days, working days and public holidays
This tool counts calendar days, including weekends. If you need to skip weekends and holidays, for example to find a delivery date "within 10 business days", use the working days calculator in "Add working days" mode. The holiday flag in the result uses the public holiday calendar of Poland, where this site is based.
To count how many days separate two specific dates, use the days between dates calculator. To check the ISO week of any date, see the week number tool.
Common mistakes when counting days by hand
The most frequent error is counting the start day, which makes the result one day too early. Another is treating every month as 30 days: 3 months from 1 November is 1 February, but 90 days from 1 November is 30 January. Leap years also catch people out - 365 days from 1 March 2027 is 29 February 2028, not 1 March, because 2028 is a leap year. The calculator handles all of this for you.
Frequently asked questions
What date is 30 days from today?
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Is the start date counted?
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What is 31 January plus one month?
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How do I subtract days from a date?
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Is 3 months the same as 90 days?
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How do I add business days instead of calendar days?
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