Days between dates calculator
Count the days between two dates, see how many days are left until a date, or add and subtract days, weeks and months.
How the days are counted
The calculator counts whole calendar days from the first date to the second. It does not count the end date unless you tick the box, which is the usual way to answer “how many days until…?”: from today to tomorrow is 1 day. When the end date is earlier than the start date, the answer is shown as a negative number of days, so you can also see how long ago something happened.
Alongside the total you get the same span as weeks and days, as months and days, the number of weekdays (Monday to Friday) and weekend days, and the total in hours. The months figure moves the start date forward one calendar month at a time, so 15 March to 20 May is 2 months and 5 days.
Adding and subtracting dates
Switch to Add or subtract to find the date a number of days, weeks, months or years from a start date, for example a 30-day notice period, a 90-day return window or a due date 40 weeks away. Tick working days only to skip Saturdays and Sundays, which is how many deadlines and delivery times are counted. Public holidays aren’t removed, because they depend on your country.
Handy facts
- A normal year has 365 days and 52 weeks plus 1 day; a leap year has 366 days.
- A year has about 260 weekdays (Monday to Friday), give or take one or two depending on the year.
- Months have 28 to 31 days, which is why “a month from now” is not always 30 days.
For developers and AI agents: GET /api/date-calc?start=2026-10-18&end=2026-12-25 or ?start=2026-10-18&add_days=30&business_days=true returns JSON, and the MCP server has a date_calc tool. Need exact times instead? Use the Unix timestamp converter.
Frequently asked questions
How many days are there between two dates?
Pick both dates above and the answer appears straight away. By default the calculator counts the days from the first date up to, but not including, the second, so Monday to Friday of the same week is 4 days. Tick “Include the end date” to count both days (5 days).
Should I include the end date?
It depends on what you are counting. For nights in a hotel, a loan period or someone’s age in days, leave it off. For days of leave, a festival or an event where you are there on both the first and the last day, include it.
How are working days counted?
Working days here are Monday to Friday. Public holidays are not removed, because they differ by country and region, so subtract any that fall in your range.
What happens when I add a month to 31 January?
February has no 31st, so the calculator uses the last day of the month: 31 January plus one month is 28 February, or 29 February in a leap year. This is the same rule most spreadsheets and banks use.
Does it handle leap years?
Yes. Every calendar day is counted, including 29 February in leap years. A year is a leap year if it divides by 4, except century years, which must also divide by 400 (2000 was a leap year, 1900 was not).