PlainwrenDate Difference Calculator
Count the time between any two dates, add or subtract days from a date, or find an exact age from a date of birth. For a dedicated age page with Hijri dates, see the age calculator.
How age and date differences are counted
The calculator counts whole calendar months first, then the days left over. It steps forward from the start date one month at a time for as long as it does not pass the end date, then counts the remaining days. Whole years are 12 of those months.
When the start date is a day that does not exist in a later month (such as the 31st), it is treated as the last day of that month. So one month after 31 January is 29 February in a leap year and 28 February otherwise.
The total number of days is the plain count of days from one date to the other. It does not include the end date, the same way that from Monday to Tuesday is one day. Tick "Count both the start and end date" to add one, which is how some contracts and leave policies count.
Worked examples
Age
Someone born on 28 February 1990 is 36 years, 7 months and 27 days old on 25 October 2026. That is 13,388 days. They were born on a Wednesday, and their next birthday is 126 days later.
Between two dates
From 31 January 2024 to 1 March 2024 is 1 month and 1 day (31 January → 29 February is one month, because 2024 is a leap year, then one more day), or 30 days in total.
Adding days
90 days after 25 October 2026 is 23 January 2027.
Leap years and 29 February birthdays
A year is a leap year if it divides by 4, except century years, which must divide by 400. So 2000 and 2024 were leap years, but 1900 was not. If you were born on 29 February, this calculator shows your next birthday as 28 February in years without a 29 February. Some countries' laws use 1 March instead for legal age.
FAQ
Why does "months" not match total days ÷ 30?
Months have 28 to 31 days, so the calendar answer (years, months, days) and the total in days measure different things. Both are shown.
Do time zones or daylight saving affect the result?
No. The tool works with calendar dates only, not times of day.
How is age counted in different cultures?
This uses the international convention: you are 0 at birth and gain a year on each birthday. Some traditional East Asian systems count differently.