Age Calculator

How it works

The calculator counts completed years since the date of birth, then completed months since the last birthday, then the remaining days. Months are counted as anniversaries — 15 March to 15 April is one month — and a birthday on a day a month does not have (such as the 31st) is counted on that month’s last day. Totals in weeks, days and hours come from the exact number of days between the two dates.

What this age calculator shows

Enter a date of birth and the calculator gives the exact age in years, months and days — the way it appears on official forms — together with the age in total months, weeks, days and hours, the day of the week you were born, how many days until your next birthday and which age you will turn, and your star sign. The second date defaults to today, but you can change it to find someone’s age on any date: when they started school, on a wedding day, or on a future date such as a retirement.

Everything is calculated in your browser; no dates are sent or stored.

How age is calculated

Age is counted in completed units. First count the full years since the birth date, then the full months since the last birthday, then the days since the last monthly anniversary.

1. Years: subtract the birth year from the current year. If this year’s birthday has not arrived yet, subtract one.
2. Months: count the whole months from the last birthday to the date. A month is complete on the same day number — 15 March to 15 April is one month.
3. Days: count the days left over after the last complete month.

Because months have 28 to 31 days, the same number of days can be “1 month, 1 day” or “1 month, 3 days” depending on the months involved. When a birthday falls on a day that a shorter month does not have — the 31st, for example — the month is counted as complete on that month’s last day.

Birthdays on 29 February

People born on 29 February have a calendar birthday only in leap years. In other years most celebrate on 28 February or 1 March, and the law differs between countries on which date counts. In many jurisdictions, including the United Kingdom, a person born on 29 February legally reaches a new age on 1 March in a common year; elsewhere it is 28 February. This calculator counts the birthday as reached on 28 February in common years and shows the exact years, months and days either way.

Your age in months, weeks, days and hours

Total months and days are useful for babies and young children, for medical and developmental milestones, and for fun facts such as your 10,000th day. For someone born on 1 January 2000, on 1 July 2026:

The 10,000-day milestone arrives at about 27 years and 4 months; 1 billion seconds at about 31 years and 8 months. The days between dates calculator finds the exact date of any such milestone.

Age for babies and toddlers

Babies’ ages are usually given in weeks for the first few months, then in months until about age two — “14 weeks”, “9 months”, “20 months” — because development changes so quickly. Enter the date of birth and read the “In weeks” and “In months” lines. Doctors and health visitors use these figures for check-ups, vaccinations and growth charts.

For babies born prematurely, clinicians often also use a corrected (adjusted) age: the age from birth minus the number of weeks the baby was born early. A baby born 8 weeks early who is 6 months old has a corrected age of about 4 months. Corrected age is commonly used for developmental milestones until about age two; ask your baby’s doctor which age to use.

How old are you if you were born in…

If you only know the birth year, your age this year is one of two numbers — the higher one once your birthday has passed:

Each year has its own page with the generation, Chinese zodiac animal, US full retirement age and upcoming milestones.

Common age milestones in the US

Rules change and have exceptions; check the official source for anything that affects you.

International age vs. traditional East Asian age

This calculator uses the international system, where a newborn is 0 and gains a year on each birthday. Traditional East Asian age reckoning counted a newborn as 1 and added a year every New Year, so a person could be up to two years “older”. South Korea officially standardised on international age for legal and administrative purposes in June 2023, and Japan and China use international age in law, though traditional counting still appears in culture and conversation.

Calculating age in Excel or Google Sheets

• Years only: =DATEDIF(A1, TODAY(), "Y")
• Years, months and days: =DATEDIF(A1,TODAY(),"Y")&" y "&DATEDIF(A1,TODAY(),"YM")&" m "&DATEDIF(A1,TODAY(),"MD")&" d"
• Total days: =TODAY()-A1

Avoid =(TODAY()-A1)/365: dividing by 365 ignores leap days and can make someone a year older a day or two early. Microsoft also notes that DATEDIF’s “MD” unit can give unexpected results at month ends, so check edge cases against this calculator.

Chronological age and “biological age”

The age this calculator gives is chronological age — time since birth. You may also see “biological age” or “body age” estimates, which try to describe how a body is ageing from tests or questionnaires. Those are estimates that vary between methods; chronological age is the only one used on documents, in law and for eligibility rules.

Common mistakes

• Only subtracting years. 2026 − 1990 = 36, but someone born in December 1990 is still 35 until their birthday.
• Dividing days by 365. Leap years add a day every four years, so the result drifts.
• Mixing up day and month. 03/04 is 3 April in most countries and March 4 in the US. The date picker avoids this.
• Counting the birth day itself. A baby is 0 days old on the day of birth and 1 day old the next day.