How to Calculate Your Exact Age and the Difference Between Two Dates

Working out your exact age or the number of days between two dates sounds easy until you meet months of different lengths and leap years. This guide shows how to do it by hand, what rules to watch for and how to check your result with an age calculator.

Calculate your age step by step

Subtract the birth date from the current date in three parts: days, then months, then years.

Example: born 15 August 1995, today is 7 November 2026.

1. Years: 2026 - 1995 = 31
2. Months: November (11) - August (8) = 3
3. Days: 7 - 15 = -8, which is negative, so borrow one month. Months become 3 - 1 = 2, and the days become 31 + 7 - 15 = 23 (October has 31 days).

The result is 31 years, 2 months and 23 days. Methods can differ by a day when they borrow days at month ends, so you can verify the result with the Age Calculator.

Count the days between two dates

• Convert both dates to a continuous day count, such as day numbers, and subtract them.
• Decide whether to include the start day, the end day or both. By default, counting the difference does not include the start day.
• Remember that months have 28 to 31 days.

For example, from 1 January to 1 March in a non-leap year is 31 + 28 = 59 days. In a leap year it is 60 days.

Leap year rules

• A year divisible by 4 is a leap year.
• But a year divisible by 100 is not, unless it is also divisible by 400.

So 2024 and 2028 are leap years, 1900 was not, and 2000 was. A person born on 29 February usually celebrates on 28 February or 1 March in non-leap years, depending on local rules.

Business days and time zones

If you need working days, exclude weekends and holidays, which a date calculator can do. If times matter, remember that time zones and daylight saving changes can shift a date when you compare moments in different regions. The Date and Time Calculator helps with these cases.

Common mistakes

• Assuming every month has 30 days.
• Forgetting to include or exclude the end date consistently.
• Ignoring leap years in long ranges.
• Mixing date formats, such as 03/04/2026, which means March 4 in some countries and 3 April in others.

Handy shortcuts

• Seven days equal one week, so divide a day count by 7 for weeks.
• A quick check for a year: 365 days, plus one in a leap year.
• Use the same date format in every calculation to avoid mix-ups.

Frequently asked questions

How many days are in a year?

A common year has 365 days and a leap year has 366. The average calendar year is about 365.2425 days.

Why do two age calculators give different results?

They may use different rules for borrowing days at month ends, or may count time of day. The difference is normally one day.

How do I calculate age in months only?

Multiply the whole years by 12 and add the remaining months. For 31 years and 2 months, that is 31 x 12 + 2 = 374 months.