Frequently Asked Questions

How DateMath works and how its calculators count. Questions about a single calculator are answered on its own page.

What is DateMath?

DateMath is a set of free date and time calculators: the date calculator, the date duration calculator, the time calculator, the hours calculator, the time card calculator, the hours to decimal calculator, the age calculator, the business days calculator, the week number calculator, the day countdown, the countdown timer, the Christmas countdown, the New Year countdown and the Halloween countdown. Each one runs in your browser: the calculators show the answer as you type, and the countdowns tick live.

Is DateMath free?

Yes. Every calculator is free to use, with no account, no sign-up and nothing to install.

Are the dates I enter stored or sent anywhere?

No. The calculations run in your browser, and the dates you type are not sent to us. They only leave the page if you copy a link to a calculation and share it, because the link carries the inputs. When someone opens such a link, our analytics may record its address, inputs included, with that page view.

Which calendar do the calculators use?

The Gregorian calendar, the one in everyday use worldwide, including its leap-year rule. It is applied to all dates, including dates before the calendar was introduced in 1582.

Do the calculators handle time zones and daylight saving time?

The calculators don't: dates and times are treated as plain calendar dates and clock times, so every visitor gets the same answer for the same link, and durations across a daylight saving change are off by the one hour the clocks moved. The countdowns read the current time from your device and count to the target in your own time zone, so a New Year countdown ends at your local midnight, and they count the real time left, with the hour of a daylight saving change in between included.

How do you count the days between two dates?

As the difference between the dates: the days after the start date up to and including the end date. From Monday to Friday of the same week is 4 days. Where it matters, a checkbox counts both the start and the end date instead (5 days in that example).

Which holidays count when calculating business days?

The 11 annual US federal holidays, on the days they are observed. Weekends are always left out; holidays can be switched off to count weekdays only.

Can I share a calculation?

Yes. Every calculator with inputs has a copy-link button ("Copy a link to this calculation", or to this countdown or timer); the link opens the same tool with the same inputs filled in. The Christmas, New Year and Halloween countdowns have no inputs, so they need none: share the page's address.