Free Age Calculator Online
The age calculator computes your exact chronological age from your date of birth in years, months, weeks, and days, as of today or any custom target date. Also includes an age gap calculator to find the age difference between two people, Korean age display, zodiac sign, and birthday countdown. Free, no account needed.
How to use the age calculator
- Select your birth month, day, and year from the dropdown menus under Date of Birth.
- Your exact age appears instantly in years, months, and days, along with total weeks, months, hours, minutes, and seconds.
- Check the birthday countdown ring to see how many days remain until your next birthday.
- Toggle "Calculate age at a specific date" to find your age on any past or future date.
- Switch to the Age Gap Calculator tab to calculate the exact age difference between two people.
How to calculate age from date of birth: the formula
Calculating age from a date of birth involves three steps applied in order:
- Count complete years: Subtract the birth year from the current year. If the birthday has not yet occurred this year (birth month/day is after today), subtract 1 more.
- Count remaining months: From the last birthday, count how many full months have passed up to today.
- Count remaining days: Count the remaining days after the last full month.
Example: Calculate age for someone born June 20, 1995 on May 3, 2026. Base years: 2026 - 1995 = 31. Their June 20 birthday has not occurred yet in 2026 (we are in May), so age = 30 years. From June 20, 2025 to May 3, 2026: 10 full months pass (July through April). From April 20 to May 3 is 13 days. Final answer: 30 years, 10 months, 13 days.
The edge cases are leap years (February has 28 or 29 days) and months with different day counts (28, 29, 30, or 31). This calculator handles all edge cases automatically, including February 29 birthdays in non-leap years, which are treated as March 1.
Age gap calculator: how to calculate age difference between two people
The age gap calculator uses the same calendar arithmetic as the age calculator but applies it between two dates of birth rather than between a birth date and today. Enter both dates of birth in the Age Gap Calculator tab to get the exact age difference in years, months, and days, along with who is older and by how many total days and weeks.
Age difference calculations are commonly needed for: relationship age gaps, sibling age spacing, comparing ages for legal or medical eligibility, HR and payroll systems, genealogy research, and academic admissions (calculating age at a specific enrollment date). The "age on date" feature in the main calculator tab handles this last case: enter the enrollment or eligibility date as the custom target date and it calculates the age at that point in time. This also works for gestational age calculations where the reference date is the due date or birth date rather than today.
Chronological age vs biological age: what the calculator measures
This is a chronological age calculator: it measures the exact elapsed time since your date of birth based on calendar dates. Chronological age is an objective, fixed number with no ambiguity. Biological age is a different concept: it estimates how old your body functions physiologically based on markers like cardiovascular fitness, cellular health, and metabolic rate. Two people with the same chronological age can have meaningfully different biological ages.
Chronological age is used in most official contexts: legal age of consent, retirement eligibility, pediatric growth charts, and clinical drug dosing calculations. For health and fitness tracking, chronological age is a useful baseline when combined with BMI and body composition data, since both BMI reference ranges and healthy body fat ranges shift with age.
Korean age calculator: the traditional age system
Korean traditional age (세는 나이) follows different rules from the international system used everywhere else. In the Korean system, everyone is counted as 1 year old at birth (not 0), and age increases by 1 on January 1 of each year, not on the individual birthday. The formula is simple: Korean age = current year - birth year + 1.
Example: someone born December 15, 2000 is Korean age 27 in 2026 (2026 - 2000 + 1 = 27). Their international chronological age on May 3, 2026 is 25 years and 4 months. The gap between Korean age and international age is typically 1 to 2 years depending on whether the birthday has occurred yet in the current calendar year.
South Korea officially standardized the international age system in June 2023, meaning legal and administrative contexts now use chronological age. However, the traditional Korean age remains widely used in social contexts and informal conversation. The calculator displays your Korean age alongside born-on weekday and zodiac sign in the Quick Info panel.
How to calculate age in Excel
Excel has a built-in DATEDIF function designed for age and date difference calculations. With a date of birth in cell A1:
- Age in complete years: =DATEDIF(A1, TODAY(), "Y")
- Remaining months after full years: =DATEDIF(A1, TODAY(), "YM")
- Remaining days after full months: =DATEDIF(A1, TODAY(), "MD")
- Combined result: =DATEDIF(A1, TODAY(), "Y") & " yrs, " & DATEDIF(A1, TODAY(), "YM") & " mo, " & DATEDIF(A1, TODAY(), "MD") & " days"
- Quick approximate age: =INT((TODAY()-A1)/365.25)
The DATEDIF function is intentionally undocumented in Excel help files (it was inherited from Lotus 1-2-3) but works in all modern versions. The "Y", "YM", and "MD" arguments handle the month and day edge cases correctly, unlike simple division by 365 which drifts over leap years.
Age and health: why chronological age matters for calculators
Chronological age is an input variable in several health calculations. BMI interpretation uses age-adjusted reference ranges for children and teenagers (the pediatric BMI percentile system). Sleep needs change with age, with teenagers requiring 8 to 10 hours and adults 7 to 9 hours. Daily water intake needs are also age-influenced, as older adults experience reduced thirst sensation and require conscious tracking. For fitness goals, knowing your exact age ensures you are using the correct reference ranges when calculating your total daily energy expenditure using the Mifflin-St Jeor formula, which incorporates age as a direct variable.
Frequently asked questions
To calculate age from date of birth, subtract the birth date from today's date using calendar arithmetic. First count complete years: a full year is credited on each anniversary of the birth date. Then count remaining complete months, then remaining days. Example: someone born March 15, 2000 calculating age on May 3, 2026 is 26 years, 1 month, and 18 days old. The age calculator automates this instantly, accounting for leap years and variable month lengths.
To calculate age manually: Step 1: Subtract the birth year from the current year to get a base number. Step 2: If the birthday has not yet occurred this year (birth month/day is after today's month/day), subtract 1. The result is the age in complete years. For the remaining months and days, count how many full months have passed since the last birthday, then count remaining days. Example: born June 20, 1995, today is May 3, 2026. Base: 2026 - 1995 = 31. Birthday (June 20) has not passed yet in 2026, so subtract 1: age = 30 years, 10 months, 13 days.
The calculator subtracts your date of birth from the current date (or a custom target date) using calendar arithmetic. It counts complete calendar years first, crediting a full year on each anniversary of your birth date, then counts remaining complete months and days. The result accounts for the actual number of days in each calendar month and correctly handles leap years, producing an exact chronological age rather than an approximation.
Chronological age is the exact amount of time elapsed since your date of birth, measured in years, months, and days. It is an objective calculation based purely on calendar dates. Biological age refers to how old your body appears physiologically based on markers like cellular health, cardiovascular fitness, and metabolic function. Two people with the same chronological age can have very different biological ages depending on lifestyle, genetics, and health history. This calculator computes chronological age only.
The age gap calculator takes two dates of birth and calculates the exact difference between them in years, months, and days. It identifies which person is older and displays the age difference along with how many total days, weeks, and months separate the two birth dates. It also shows each person's current age. Switch to the "Age Gap Calculator" tab in the tool and enter both dates of birth to use it.
Yes. For people born on February 29 (leap day), the calculator treats March 1 as the birthday in non-leap years. This follows the most common legal convention. In leap years, February 29 is recognized as the actual birthday. The birthday countdown uses the same logic: if today is February 28 in a non-leap year and your birthday is February 29, the calculator correctly shows 1 day until your next birthday on March 1.
Korean traditional age (세는 나이) counts everyone as 1 year old at birth and adds 1 year on every January 1, regardless of individual birthdays. The formula is: Korean age = current year - birth year + 1. For example, someone born in December 2000 is Korean age 27 in 2026 (2026 - 2000 + 1 = 27), even if their international age is still 25. Korea officially abolished the traditional age system in June 2023 in favor of the international standard, but it remains widely used culturally. The calculator displays your Korean age in the Quick Info section.
To calculate age in Excel from a date of birth in cell A1, use the DATEDIF function: =DATEDIF(A1, TODAY(), "Y") returns the age in complete years. For years and months: =DATEDIF(A1, TODAY(), "Y") & " years, " & DATEDIF(A1, TODAY(), "YM") & " months". The "Y" argument returns complete years, "YM" returns remaining months after the last full year, and "MD" returns remaining days. Alternatively, use =INT((TODAY()-A1)/365.25) for a quick approximate age in years.
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