Date Difference Calculator

Counting the days between two dates

How many days until the notice period ends? How old is a loan in months? Is the cheque still within its three month validity? When does a 90 day return window close? Counting on a wall calendar is slow and easy to get wrong, because months have 28, 29, 30 or 31 days and every fourth year has an extra day. This calculator does the counting for you and shows the answer in the forms people actually ask for: years, months and days; total days; whole weeks; and working days.

How to use it

1. Pick a start date and an end date. If the end date comes first, the difference is simply counted backwards.
2. Tick Include the end date when both days count, for example a hotel booking or a leave application from Monday to Friday inclusive. Without it, the count runs up to the end date but not through it, the way an age or an interest period is counted.
3. Tick Saturday is a working day if your office, bank branch or school works six days a week.
4. In the second box, add or subtract a number of days, weeks, months or years from any date to find a deadline or a due date.

The rules it follows

Years, months and days are counted from the start date: the calculator finds how many whole months fit before the end date, then counts the days left over. From 15 May 2020 to 20 August 2024 that is 4 years, 3 months and 5 days.

Months do not all have the same length, so adding a month needs a rule. Here it is: when adding months or years lands on a day the target month does not have, the result is the last day of that month. So 31 January plus one month is 28 February, or 29 February in a leap year, and 29 February 2024 plus one year is 28 February 2025. Two months after 31 January is 31 March, because each addition is counted from the original date and not one month at a time. Spreadsheet functions such as EDATE use the same rule, so results here match what you get in Excel or Google Sheets.

Business days count Monday to Friday, and Saturday too if you tick it. Public holidays are not removed, because they differ by state, by bank and by employer; subtract your own holiday list from the figure shown.

A worked example

A tenant gives notice on 2 November 2026 and the agreement asks for two months. Add 2 months to 2 November 2026 and you get Saturday, 2 January 2027. Back in the first box, from 2 November 2026 to 2 January 2027 is 61 days, or 8 weeks and 5 days, of which 45 are Monday to Friday working days.

How it works and privacy

The calculator turns each date into a plain day count, the number of days since 1 January 1970, using the Gregorian calendar with its leap year rule: every fourth year, except century years that are not divisible by 400. Working with whole calendar days means time zones and daylight saving changes cannot shift a result by a day, which is a common bug in date code that works with hours. Everything runs in your browser, and Ur Next Door does not see the dates you enter.