By ToolzHive
About this tool
The date calculator finds the date a number of days, weeks, months or years before or after another date. It handles month lengths and leap years correctly, can count business days only (skipping weekends) for deadlines and delivery times, and shows the weekday, ISO week number and day of the year for the result.
How to use Date Calculator (Add & Subtract)
- Choose the start date and whether to add or subtract.
- Enter the years, months, weeks and days to add or subtract.
- Tick business days to skip Saturdays and Sundays, then read the result date.
Worked example
Adding 90 days to September 26, 2026 gives Friday, December 25, 2026. Adding 10 business days to a Monday lands on the Monday two weeks later.
Example: add or subtract calendar days
Starting from October 1, 2026, adding 14 calendar days gives October 15, 2026; subtracting 14 days gives September 17, 2026. Check the selected operation before copying a deadline into a calendar.
Business days and holidays
The business-day option skips Saturdays and Sundays. It does not load public holidays or workplace calendars. For a contractual or legal deadline, confirm the applicable counting rules and holidays separately.
Months have different lengths
Adding a month differs from adding 30 days. Near a month end, inspect the resulting date because the destination month may not contain the same day number. Keep the starting date and selected units with your calculation.
How are months added to dates like January 31?
If the target month is shorter, the date moves to its last day: January 31 + 1 month = February 28, or February 29 in a leap year.
Does it include public holidays?
Business-day mode skips weekends only. Public holidays vary by country, so subtract them yourself for exact deadlines.
What is the ISO week number?
The ISO standard numbers weeks from Monday to Sunday, with week 1 being the week that contains the first Thursday of the year.
Put this guide into practice
- Date Calculator (Add & Subtract) — Add or subtract days, weeks, months and years from a date, with an optional business-days mode.