Date & Duration Calculator

Work with dates: count the days between two dates, add or subtract a duration, get someone's exact age, and look up the ISO week number, day of year and other facts about any date.

Runs entirely in your browser. Nothing you put in here gets uploaded.

Days between two dates

How far apart two dates are, as calendar units and as plain totals. Leave the start empty to count from today.

Start date

End date

Include the end date, so 1 January to 2 January counts as 2 days

Difference

Pick an end date to compare against the start

Add or subtract a duration

Move a date by years, months, weeks and days, for deadlines like a date plus 90 days. Leave the start empty to count from today.

Start date

Years

Months

Weeks

Days

Result

Pick a start date

Result date

The resulting date shows here as YYYY-MM-DD

Age calculator

An exact age from a birth date, with the countdown to the next birthday. Set the second date to get the age at any other point in time.

Birth date

Age as of

Exact age

Pick a birth date

Date facts

The week number, day of year, quarter and other facts about any date. Leave the field empty for today.

Date

Pick a date to see its facts.

About the Date & Duration Calculator Tool

This tool answers the everyday date questions in one place. Count the days between two dates, move a date forward or back by a duration, work out an exact age, and look up facts like the ISO week number for any date.

Every date can be typed straight into its field or picked from a calendar, and a start date left empty counts from today.

What you can do

Count the days, weeks and working days between two dates.
Add or subtract years, months, weeks and days from a date.
Find the date 90 days from today, with its weekday.
Calculate an exact age in years, months and days from a birth date.
See the days until the next birthday and the total days lived.
Look up the ISO week number, day of year and quarter of any date.

How to use the Date & Duration Calculator

1Go to the card that matches your question. Each card works on its own.
2Type each date as YYYY-MM-DD or pick it from the calendar. A start date left empty means today.
3Read the answer as a sentence and copy any value with its copy button.

How the difference is counted

The gap between two dates is shown in two ways. The calendar breakdown counts whole years and months first and then the days that remain, which is how people state ages and anniversaries. The totals count plain days, full weeks, working days from Monday to Friday, hours and minutes. By default the end date itself is not counted, so 1 January to 2 January is 1 day. Turn on the end date toggle to count it as well, which is common for bookings and billing.

Months of different lengths

Adding months keeps the day of the month where it can. When the target month is shorter, the date is clamped to that month's last day, so 31 January plus one month lands on 28 February, or on 29 February in a leap year. The tool points it out whenever this happens. The same rule decides that a 29 February birthday is celebrated on 28 February in non-leap years.

ISO week numbers

Week numbers follow ISO 8601, where week 1 is the week that contains the year's first Thursday and weeks start on Monday. That is why the first days of January can still belong to the last week of the previous year, and 29 to 31 December can already sit in week 1 of the next one. To turn a date into a Unix timestamp instead, use the Unix Timestamp Converter.

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