How this works

The calculator finds the exact difference between two dates by working through the calendar directly — counting full years first, then full months within the remaining span, then remaining days. This handles the messiness of real calendars: months of different lengths, February's 28 or 29 days, and the fact that "one month later" means something different depending on which month you start in.

The total days and weeks figures count every actual calendar day between the two dates, making them straightforward to verify with any calendar.

What you can use this for

Exact age calculation

Enter a birth date and today's date to get the exact age in years, months, and days — more precise than just subtracting birth year from current year, which ignores whether the birthday has passed yet this year.

Countdown to an event

Set the start date to today and the end date to a future event (a wedding, a deadline, a trip) to see exactly how many days you have. The total days figure is the clearest number for this.

Duration of a project or period

Enter the start and end date of any span — an employment period, a lease, a contract, a health condition — to find exactly how long it lasted.

Checking someone's eligibility

Age thresholds matter in many contexts — retirement, school enrollment, insurance, legal requirements. The exact years-months-days breakdown removes any ambiguity about whether a cutoff date has been reached.

How months are counted

Month counting in date arithmetic is less obvious than it seems. From January 31 to February 28 is one month. From January 31 to March 31 is two months exactly. The reason: a "month" is counted only when the same day-of-month has been reached in the next month. If the start date is on the 31st and the next month has only 28 or 30 days, the month completes on the last day of that shorter month.

Frequently asked

Does this account for leap years?

Yes — all calculations use actual calendar dates, so February 29 is counted as a real day when it exists, and the total day count between any two dates is always exact regardless of leap years in between.

Can I use this for something other than a birthday?

Yes — any two dates work. Work anniversaries, contract durations, time since a medical event, days until a deadline, length of a trip — enter any start and end date and the calculator returns the exact span.

Why do years + months + days sometimes not add up to the total days?

They measure different things. Total days is a simple count of every day in the span. Years/months/days breaks the same span into calendar units — which don't all have the same number of days. A "month" in the result could be 28, 29, 30, or 31 days depending on which month it falls in.

What if I enter the dates in the wrong order?

If the "compared to" date is earlier than the start date, the results will show a negative span. Just swap the dates if you see that happening.