Your age is based on the amount of time that has passed between your date of birth and a chosen date, usually today.
Although age is often shown as a number of years, it can also be calculated more precisely in years, months and days.
In this guide, you’ll learn how to calculate your age, understand how dates affect the result, and see how to work out your exact age more accurately.
How Is Age Calculated?
Age is calculated by comparing your date of birth with the current date, or with another date you choose.
A simple age calculation starts with:
Age = Current Year − Birth Year
However, this only gives the correct answer if your birthday has already happened in the current year.
For example, if you were born in 1990 and the current year is 2026:
2026 − 1990 = 36
But if your birthday has not happened yet in 2026, your age would still be 35.
That is why an exact age calculation also checks the month and day.
How to Calculate Your Age: A Simple Step-by-Step Guide
By ToolNestPro | Updated September 2026
How to Calculate Your Exact Age
To calculate your exact age, you need to compare the year, month and day of your birth date with the date you are measuring from.
For example, if you were born on:
15 March 1990
and the current date is:
3 October 2026
your age is:
36 years, 6 months and 18 days
If the current day is earlier than your birth day, you may need to borrow days from the previous month. The same idea applies when the current month is earlier than your birth month.
Because months have different numbers of days, calculating exact age manually can become confusing.
That is why an age calculator is useful when you want a precise result in years, months and days.
Common Age Calculation Mistakes
Age calculations can seem simple, but small date differences can easily cause errors.
Common mistakes include:
subtracting only the birth year from the current year
forgetting whether the birthday has already happened this year
ignoring the month and day when calculating exact age
using the wrong date format
forgetting that months have different numbers of days
making mistakes around leap years
For example, someone born in December 1990 is not automatically 36 throughout all of 2026. They only turn 36 once their birthday arrives in December.
Using the full date of birth gives a much more accurate result.
Calculate Your Age Online
Want to work out your exact age in years, months and days?
Use our free Age Calculator to enter your date of birth and quickly calculate your age based on today’s date.
Frequently Asked Questions
How do I calculate my age from my date of birth?
Subtract your birth year from the current year, then check whether your birthday has already happened this year. If it has not, subtract one year.
Can age be calculated in years, months and days?
Yes. A more precise age calculation compares the full birth date with the current date to show the result in years, months and days.
Do leap years affect age calculations?
They can affect exact calculations involving days, especially for people born on or around 29 February.