How to calculate your exact age and the days between two dates

How old are you in years, months and days? How many days are left before a deadline? How many working days between two dates? These questions come up in forms, job applications, school admissions, legal notices, project plans and notice periods, and they are harder than they look because months have different lengths and years sometimes have an extra day. The free Age & Date Difference Calculator answers them in your browser with exact counting rules. This guide explains how dates are counted, so you know when the answer is the one you need.

Two modes

The tool has two modes:

• Age from date of birth. Enter a date of birth. The second date starts as today, read from your own device, and you can change it to ask "how old was I on this date?" or "how old will I be on that date?"
• Days between two dates. Enter any two dates and read the difference, with the totals in days, weeks and months and the number of working days.

How age in years, months and days is counted

The calculator works like a person counting on a calendar:

1. Count the whole years from the first date.
2. Then count whole months from there.
3. The days left over are the days.

For example, from 15 August 2000 to 16 October 2026:

• 26 years take you to 15 August 2026.
• 2 more months take you to 15 October 2026.
• 1 more day takes you to 16 October 2026.

The result is 26 years, 2 months and 1 day. The tool also gives the totals: 9,558 days, which is 1,365 weeks and 3 days, and 314 whole months. And it shows the next birthday: from 16 October 2026 your 27th birthday is 303 days away.

Month ends and leap years

Edge cases are where hand counting goes wrong, so it is worth knowing what the tool does.

A start date on the 31st. If you count one month from 31 January, there is no 31 February. The calculator lands on the last day of the shorter month. So from 31 January to 1 March 2026 the result is 1 month and 1 day (31 January plus one month is 28 February, and one more day is 1 March), and it is 29 days in total.

Born on 29 February. In years that are not leap years, the birthday is treated as 28 February. Someone born on 29 February 2000 is 26 years, 0 months and 1 day old on 1 March 2026, having had their 26th birthday on 28 February. They have only a true birthday on 29 February every four years, but they still age every year.

Leap years generally. A year has 366 days when it is divisible by 4, except century years that are not divisible by 400. So 2000 and 2024 are leap years, 1900 and 2100 are not. This is why dividing the number of days by 365 gives a slightly wrong number of years. The calculator counts calendar years and months instead.

Counting days: are both ends included?

There are two ways to count the days between two dates, and sites differ. The tool counts full calendar days between the two dates: from 1 October to 31 October is 30 days. That is the same as subtracting the dates. If you want to count both the first and last day (for example, a hotel stay's days of occupancy or an inclusive leave period), add one. If another site shows a different answer for age in days, this is usually why, or because it includes the time of day.

Working days

For the second mode, the tool also gives working days: Monday to Friday, counting both the start and the end date if they fall on a weekday. October 2026 has 22 working days (it starts on a Thursday and has 31 days). A full year such as 2026 has 365 days and 261 weekdays.

Holidays are not removed. Public holidays differ by state, religion and company, so the tool can't know them. To plan a deadline, subtract your holidays from the working-day total yourself. If your company works on Saturdays or has a different weekend, adjust the count in the same way.

Everyday uses

• Filling forms. Admissions, passports, exam applications and insurance forms ask for age on a given date. Enter that date as the second date.
• Eligibility. Check if someone will be old enough (or not too old) on a deadline, such as the cut-off date of an exam.
• Notice periods and probation. Work out the last working day from a start date and a number of days or months.
• Project planning. Days and working days between a start and a delivery date.
• Contracts and warranties. How many days remain? When does a 90-day return period end?
• Pregnancy, courses and subscriptions. Weeks between two dates.
• Birthday countdowns and anniversaries.
• Family trees and history. Age at a past event.

Using the tool

1. Open the Age & Date Difference Calculator.
2. Choose Age from date of birth or Days between two dates.
3. Pick the two dates. The second starts as today.
4. Read the exact difference, the totals in months, weeks and days, and either the next birthday or the number of working days.

Your dates are not stored or sent anywhere. The calculation runs in your browser, which also matters because a date of birth is personal information.

Timestamps and time zones

The tool works with calendar dates, not times. If you need the difference to the second, or you are comparing times in different time zones, use Unix timestamps with the Unix Timestamp Converter. A date in one time zone can be a different date in another, and "today" comes from your device clock, so check it if the date looks wrong.

Calculating dates in code

Developers meet the same rules in programming. PHP has a DateTime class with diff(), covered in the dates and times lesson, and MySQL has DATEDIFF and TIMESTAMPDIFF, covered in Date and time functions. The edge cases above are exactly the ones to test in your own code: month ends, 29 February and the first and last days of the year.

Common mistakes

• Dividing the number of days by 365 to get years.
• Forgetting that months have different lengths.
• Counting the end date when the rule says not to, or the reverse.
• Treating Saturday as a working day when the company does not.
• Not removing public holidays from working-day counts.
• Using today's date from a device with the wrong clock.
• Entering dates in the wrong order and getting a negative or reversed result.

Related tools

If your dates are for a loan or a deposit, the EMI Calculator and the FD & RD Calculator work in months. To compute a percentage of a period, use the Percentage Calculator. To write a date or number in words for a document, the Number to Words Converter helps.

Quick answers

How is exact age calculated? Whole years first, then whole months, then the leftover days.

What if I was born on 29 February? In non-leap years the birthday is treated as 28 February.

Are public holidays excluded from working days? No. Only weekends are excluded; remove holidays yourself.

Does it count both the start and end date? Days are counted as the difference between the dates. Working days include both ends if they are weekdays.

Is my date of birth stored? No. Everything is calculated in your browser.