Date Calculator

Add to a date or count the days between two

Date Calculator has three tabs. Add or subtract moves a date forward or back by days, weeks, months or years. Difference measures the gap between two dates, and Working days counts Monday-to-Friday days.

It works with calendar dates, not times of day, so a daylight-saving change can’t shift an answer. Dates from the year 1000 to 9999 are accepted, and the sums run in your browser.

How to calculate a date or a span of days

1. Pick a tab. Start date and both From boxes begin on today, and the To boxes on the date a month from today.
2. In Add or subtract, choose Add or Subtract, enter an Amount — a whole number up to 1,000,000 — and select Days, Weeks, Months or Years.
3. In Difference, set From and To in either order; if To comes first, the result points that out.
4. In Working days, set From and To, and tick Include the end date when the last day should count.
5. The answer refreshes as you change any field; there’s no button to press.

What the answer tells you

• New date: written out with its weekday, plus the YYYY-MM-DD form and the sum you asked for.
• Short months: if adding months or years lands on a day the month lacks, the month’s last day is used and a note says so.
• Difference: the total days in large type, then the same gap as weeks and days, and as years, months and days.
• Working days: the weekday count, plus the weekend days and total days in the span.

Everyday date questions it answers

• Due dates: the day that falls 30 days or 6 weeks after an invoice, order or notice.
• Countdowns: how many days remain until an exam, a trip or a launch.
• Notice periods and project plans: the weekdays between two dates, before you allow for holidays.
• Renewals: when a yearly contract comes round again.

Getting the count you need

• Difference never counts both ends: Monday to the following Monday is 7 days. Add one if your form wants the first and last day included.
• Working days counts the start date when it falls on a weekday, but the end date only with Include the end date ticked — Monday to Friday of one week gives 4, or 5 with the box ticked.
• Public holidays, company closures and other weekend patterns aren’t known to the calculator, so take those days off yourself.

Why month lengths change the answer

Adding months near the end of a month

Add or subtract keeps the day of the month where it can, and otherwise falls back to the month’s last day: 31 January plus one month gives 28 February, or 29 February in a leap year.

Counting whole months between dates

The years, months and days line in Difference follows the rule used by the Age Calculator: a monthly anniversary that would fall on a missing day is reached on the 1st of the next month. So 31 January to 1 March counts as exactly 1 month, while 31 January to 28 February is 0 months and 28 days.

Date Calculator: common questions