How to Calculate Your Age: Exact Age in Years, Months and Days

What is your exact age?

Your age in years is the number of birthdays you have already celebrated. Your exact age goes one step further. It counts the full years, then the full months since your last birthday, and then the remaining days.

For example, a person who is 28 years, 1 month and 14 days old has had 28 birthdays, and 1 month and 14 days have passed since the last one. This is often called chronological age, and it is the version that schools, hospitals and government offices use when they need precision.

How to calculate age from date of birth step by step

You can calculate age by hand in three steps. Write both dates as day, month and year, then subtract the date of birth from the date you want to measure. Start with the days, then the months, then the years, because any borrowing moves from right to left.

• Step 1: Subtract the days. Subtract the birth day from the current day. If the answer is below zero, add the number of days in the month before the current month, and remember to take 1 away from the months in the next step.
• Step 2: Subtract the months. Subtract the birth month from the current month, including the 1 you carried. If the answer is below zero, add 12 and remember to take 1 away from the years.
• Step 3: Subtract the years. Subtract the birth year from the current year, including the 1 you carried. The three results together are your exact age.

A worked example

Suppose someone was born on 20 August 1998 and you want to know their age on 4 October 2026.

Days: 4 minus 20 is negative 16, so add 30 (September has 30 days) to get 14 days, and carry 1 month. Months: 10 minus 8 is 2, and taking away the carried month leaves 1 month. Years: 2026 minus 1998 is 28.

The exact age is 28 years, 1 month and 14 days. You can double check it by counting forward: 20 August 2026 is exactly 28 years after the birth date, 20 September is one month later, and 4 October is 14 days after that.

How leap years affect your age

A normal year has 365 days, but a leap year has 366 because 29 February is added. A year is a leap year when it can be divided by 4, except century years such as 1900, which are leap years only when they can be divided by 400. That is why 2000 was a leap year and 1900 was not.

Leap days matter when you count your age in days. A person who has just turned 30 has lived about 10,957 or 10,958 days, not 10,950, because 7 or 8 leap days have been added along the way. Leap years do not change your age in years, months and days, because the calendar already takes care of them.

People born on 29 February only see their exact birthday every four years. In the other years the legal birthday depends on the country, and some places use 28 February while others use 1 March.

Where do you need your exact age?

An exact age is more than a curiosity. These are common situations where it matters:

• School admission. Many schools set a cut-off date and check whether a child has reached a minimum age on that day.
• Job and visa applications. Forms often ask for your age on a specific date, such as the closing date of a vacancy.
• Retirement and pensions. Pension rules are based on exact age, so being a few months short can change when you qualify.
• Health and babies. Doctors track the growth of babies in weeks and months, not only in years.
• Legal ages. Voting, driving and marriage ages differ from country to country and are counted from your exact birth date.

Age in months, weeks, days and hours

Sometimes years are not enough. To find your age in other units, use these simple rules:

• Months. Multiply your full years by 12 and add the extra months.
• Weeks. Find the total number of days between the two dates and divide by 7.
• Days. Count the days between the date of birth and the chosen date, including leap days.
• Hours. Multiply the total number of days by 24.

A fun milestone is your 10,000th day, which arrives at about 27 years and 4 to 5 months of age.

Common mistakes when calculating age

• Counting only the years. Subtracting the birth year from the current year gives the wrong age when your birthday has not happened yet this year.
• Using 30 days for every month. Months have 28 to 31 days, so use the real length of the previous month when you borrow days.
• Forgetting leap days. Multiplying years by 365 leaves out the extra leap days and gives a slightly low total.
• Mixing up date formats. A date such as 04/10/2026 means 4 October in many countries and 10 April in others, so always check the order.

Calculate your age instantly

Doing the sums by hand is useful for understanding the method, but it is easy to slip, especially with month lengths and leap years. An online age calculator does the borrowing for you, shows your age in years, months and days, counts the days until your next birthday and lets you check your age on any past or future date.

Our age calculator works in your browser, so your date of birth is never sent to a server.

Frequently asked questions