Time Calculator

What the time calculator does

This works out a date by adding or taking away an amount of time from a starting one. You give it a date to start from, say whether you are going forward or back, and set how much time to move by in years, months, weeks, and days. It hands you the date you land on. It is the tool for the everyday question of what date falls a certain stretch of time before or after another.

How to use it

1. Start Date. The date you are counting from.
2. Operation. Add to move into the future, or Subtract to move into the past.
3. Years, Months, Weeks, Days. How much time to move by. Fill in any of them.

Press Calculate for the resulting date, or Reset to clear the fields.

Stacking years, months, weeks, and days

The handy part is that the four boxes work together in a single calculation, so you are not limited to one unit at a time. You can ask for one year, two months, and ten days all at once, and it applies the whole lot from your start date in one go. That makes it easy to express an amount of time the way you naturally think of it, rather than converting everything into days first. Leave a box at zero and it simply adds nothing for that unit, so you only fill in the parts you need.

Counting forward and counting back

The Add and Subtract switch is what lets the same tool answer two opposite questions. Add tells you where you end up a stretch of time from now, like the date a deadline falls due. Subtract tells you where you started, like the date something began given how long ago it was. So the same amount of time, say 90 days, can give you either the day 90 days ahead or the day 90 days past, just by flipping the operation. One small thing to keep in mind: because months vary in length, adding a number of months lands you on the same day in a later month, which near the end of a month can shift by a day or two when that day does not exist.

Where it earns its keep

Anywhere a date depends on an amount of time. Working out when a deadline falls from a start date, the end of a notice period, or when a trial or subscription renews. Counting back to find a start date from an end date and a duration. Planning a milestone a set time ahead. It takes the awkward mental arithmetic of carrying across months and years and just gives you the date.

Questions people ask

Can I add years, months, and days at the same time?

Yes. The four fields are applied together in one calculation, so you can move by a mix of units, like one year and two months and ten days, in a single step.

Can it count backwards?

Yes. Choose Subtract instead of Add and it moves into the past, giving you the date that amount of time before your start date.

How are weeks handled?

A week is treated as 7 days, so two weeks simply moves you 14 days. It is there as a convenience so you do not have to convert weeks into days yourself.

What happens near the end of a month?

Adding months keeps the same day number in the later month, so moving from the 31st into a shorter month can land a day or two off, since that exact date does not exist there.