Comprehensive Calculator Guide
This calculator finds the date a number of days, months or years after or before a given date, with the day of the week. 90 days after 1 January 2026 is Wednesday 1 April 2026. Use it for contract end dates, probation periods and payment deadlines.
Days, months and years
Days are counted on the calendar, so months of different lengths are handled for you. Enter a negative number of days to count back: 40 days before 17 October 2026 is Monday 7 September 2026. The start date itself is not counted.
Adding a month moves to the same day of the next month rather than adding 30 days. When that day does not exist, you get the month's last day: 31 January 2026 plus one month is 28 February 2026.
How to Use
- 01Pick the start date.
- 02Enter years, months or days, or any mix. Use negative days to go back.
- 03Read the resulting date and weekday.
Formula Used
Result = start date + years and months (on the calendar) + daysPractical Examples
Example 1: a 90-day deadline
From 1 January 2026: Wednesday 1 April 2026.
Example 2: counting back
40 days before 17 October 2026: Monday 7 September 2026.
Example 3: a year and six months
From 17 October 2026: Monday 17 April 2028.
Important Tips
- Check whether your contract counts the start day.
- For working days only, use the business days calculator.
Common Mistakes to Avoid
- Treating every month as 30 days.
- Forgetting the minus sign when counting back.
Frequently Asked Questions
- What date is 90 days from today?
- Pick today's date and enter 90 days.
- How do I subtract days?
- Enter a negative number, such as −40.
- Is adding a month the same as adding 30 days?
- No, it moves to the same day of the next month.