Add to or Subtract from a Date Using Years, Months, Days and Hours

This online calculator performs the addition or subtraction of a date. You can find the resulting date by adding one or more numbers (years, months, weeks, days and hours) to the starting point to discover a future date, or by subtracting them to find a past date.

Using it to calculate a date

You can calculate the exact date by adding days, months or hours, including minutes and seconds.

Example: calculating a date by adding or subtracting numbers

For example, we have a starting date of 03/09/1984. We want to add 45 days to this date. Just put 45 in the days box. We can now calculate the result and we get: 04/23/1984.

You can enter several values at once. For example, subtracting 3 months and 78 days. The result is: 09/22/1983.

It also works perfectly with hours, and by combining hours, minutes, days, weeks…

Year format

In the date field, the year must be entered correctly. Enter 01/01/2019 and not 01/01/19. If we want to use the date 11/27/511, we must enter 11/27/511.

Negative years

You can use dates with a negative year (before the birth of Christ) by inserting a "-" before the year. For example: 10/01/-607.

How to choose between addition and subtraction?

This calculator has two buttons. Just click the appropriate button to calculate: Add or Subtract.

Use cases: flight time, historical chronology and intermittent fasting

Flight time

For frequent flyers, this calculator is very handy. It tells you at what time you will land. For example, you take a plane from New York to São Paulo, Brazil. The trip takes about 9 hours and 50 minutes. If you leave on July 25 at 10:30 PM, the calculator determines your arrival day and time: July 26 at 8:20 AM, New York time.

To find the time in the São Paulo time zone, you can use the tool again. The time difference is about +1 hour compared to New York. So, using this tool and adding 1 hour, we get July 26 at 9:20 AM.

Historical chronology

You can use this tool for historical research or calculations involving the addition or subtraction of dates. For history and chronology fans, this tool is a great asset.

Calculating an intermittent fasting window

This type of intermittent fasting involves eating during a set period and letting the body detox by fasting for 16 hours each day. For example, if we eat our last meal at 7 PM, this calculator determines when to break the fast. By adding 16 hours, it gives us 11 AM the next day, which corresponds to a proper intermittent fast.

Other cases

Of course, there are other cases where this calculator is very useful. Ultimately, it is handy for any activity that requires adding to or subtracting from one or more dates.

To calculate the number of days, months or years between two dates, use our days between two dates tool instead. And to add or subtract only hours, minutes and seconds, check out the time calculator.

Carry and the "Keep values" option

The Carry button copies the obtained result into the starting date field, which lets you chain several successive calculations from the new date. The Auto carry option does this automatically after each calculation.

The Keep values option, enabled by default, keeps the entered numbers (years, months, days, hours…) after a carry: you can then add or subtract the same duration several times without retyping it at each step. If you disable it, these fields are reset to zero at each carry.

Reset, save and export

You can reset the data by clicking the Clear button.

Your data is automatically saved in a table that you can export in CSV or PDF format. This table is also editable, so you can add notes or comments to it.

Frequently asked questions (FAQ)

How do I add days to a date?

Enter your starting date, type the number of days in the "Days" field, then click "Add". The calculator immediately displays the resulting date. You can also combine several units: years, months, weeks, days, hours, minutes and seconds.

How do I calculate a past date?

Enter the starting date and the duration to remove (days, months, years…), then click "Subtract". The tool calculates the corresponding earlier date, including for very old dates or negative years (BC).

Can I calculate with hours, minutes and seconds?

Yes. In addition to the date, you can enter a starting time and then add or subtract hours, minutes and seconds. It's handy for calculating an arrival time, a time difference or an intermittent fasting window.

What are the "Carry" and "Keep values" options for?

"Carry" copies the result as the new starting date to chain calculations, and "Auto carry" does this automatically after each calculation. The "Keep values" option, enabled by default, keeps the entered numbers after a carry so you can reuse the same duration without retyping it.

Is the date calculator free?

Yes, the tool is completely free and usable online, with no sign-up. Your calculations are also saved in a table that you can export in CSV or PDF format.