What Is Age?
Your age is the time since you were born. Most countries count it in whole years that go up by one on each birthday, so someone who has lived 3 years and 11 months is 3 until their next birthday. An exact age, or chronological age, also counts the months and days since the last birthday.
- Age in years: the number people usually give, used for school starting ages, driving, voting and retirement.
- Exact age: years, months and days, as asked for on some forms and for babies and young children.
- Age in days, weeks or seconds: the same time counted in smaller units, for fun milestones like your 10,000th day.
Some cultures count age differently, for example starting at 1 at birth. This calculator uses the common system where age goes up on your birthday.
How to Calculate Age
There's no single formula, because months have different lengths. Count it in steps instead, from the date of birth to the date you want:
- Years: count the birthdays that have passed.
- Months: from the last birthday, count the whole months, each one ending on the same day of the month as the birth date.
- Days: count the days that are left.
When the birth date is later in the month than a short month allows, such as the 31st, that month ends on its last day instead: one month after Jan 31 is Feb 28. Someone born on Feb 29 has their birthday on Feb 28 in other years. For a total in days, count every day between the two dates; weeks are days ÷ 7, and hours are days × 24.
Example
Someone born on Monday, Feb 28, 2000, on Mar 31, 2026:
- Years: the 26th birthday was on Feb 28, 2026, so 26 years.
- Months: 1 month later is Mar 28, 2026, so 1 month.
- Days: from Mar 28, 2026 to Mar 31, 2026 is 3 days.
- In total: 26 years, 1 month and 3 days, which is 9,528 days or 1,361 weeks and 1 day.
How to Use the Age Calculator
"I was born on July 15, 1990. How old am I today, exactly, and when is my next birthday?" This calculator answers that.
Let's enter the dates for this example in each box. They are already filled in when the calculator opens, so you can follow along and then change them to your own.
- Date of Birth: Enter July 15, 1990, which is the day you were born. Any date from the year 1000 on works.
- Age on Date: This shows today's date. Change it to find an age on another day, such as a birthday in the past or a retirement date in the future. It can't be before the date of birth.
Calculate and Reset
Click Calculate to see your results. If a box has a problem, such as an empty date or an age on date before the birth date, a message pops up under that box instead. You get:
- Your Results: your age in years, months and days, the total in days and weeks, the day of the week you were born, and when your next birthday comes.
- Age today: the headline number, your age in whole years.
- Exact Age: years, months and days, such as 26y 1m 3d.
- Total Days, Next Birthday and Day of the Week Born: the days lived so far, the days until your next birthday, and whether you were born on a Monday or a Sunday.
- Other Units: the same age as months and days, weeks and days, days, hours, minutes and seconds.
- Milestones: the next round numbers, such as 10,000 days old or 1 billion seconds old, and round birthdays, with their dates.
- Share Results: a link that opens this calculator with both dates filled in. Copy it, or share it on Facebook or X.
Click Reset to go back to the example birth date and today. Ages are counted in whole calendar days, not by the time of day you were born.