Date Calculator
Work out how much time lies between two dates —in years, months and days, plus the total number of days and weeks— or add and subtract days, weeks, months or years to a date to find out which day it lands on. Perfect for working out an age, a length of service, a deadline or a due date. Everything happens in your browser, with no accounts and no connection.
How to calculate with dates
- Choose the mode: “Difference” between two dates or “Add or subtract” to a date.
- In “Difference”, pick the start date and the end date; you will see the years, months and days between them, plus the total number of days and weeks.
- In “Add or subtract”, choose a date, type an amount (negative to subtract) and the unit; you will see the resulting date and its day of the week.
- Tick “Include the end day” if you want to count the last day too in the difference.
Frequently asked questions
How is the difference between two dates calculated?
It first counts the whole years that fit between the two dates, then the whole months, and finally the leftover days. So the result (for example, “2 years, 3 months and 5 days”) matches the natural way of measuring time. It also shows the exact total number of days, which is handy for deadlines.
Does it include the end day?
By default no: the difference is the days elapsed between the start and end date (from 1 to 2 January is 1 day). Tick “Include the end day” to also count the last day, which is common when working out the length of a stay, an event or a holiday.
How do I work out an age or length of service?
Use “Difference” mode: put the birth (or start) date as the start date and today’s date as the end date. The breakdown in years, months and days is the exact age or length of service.
How do I add or subtract days from a date?
Switch to “Add or subtract” mode, choose the starting date, and type the amount and unit (days, weeks, months or years). To subtract, type a negative number. You will see the resulting date and which day of the week it falls on.
Does it account for leap years?
Yes. It uses the real calendar, including 29 February in leap years. When adding months or years, if the starting day does not exist in the target month (for example, the 31st in a 30-day month, or 29 February in a non-leap year), it is adjusted to the last day of that month.
Does it use my time zone?
No. The tool works only with calendar dates, without a time of day, so the result does not depend on your time zone or on daylight saving changes. It is the same calculation wherever you are.
Is anything sent to a server?
No. All calculations are done in your browser with JavaScript; the dates you enter never leave your device and the tool works offline once loaded.