Why use this calculator
Most of the time you only need your age in whole years, but plenty of forms and decisions need more precision than that. Insurance and superannuation applications, visa and working holiday eligibility, school starting ages, junior sport age groups, pension and retirement dates and some medical dosing all hinge on an exact date, and being one day short of a cut-off is the same as being a year short.
Counting it by hand goes wrong in predictable places: months have different lengths, leap years add a day, and borrowing days from the previous month trips people up. This calculator does the calendar arithmetic properly, handles 29 February birthdays and impossible dates cleanly, and adds the totals and countdown people usually want next.
How to use it
- Enter your birth year as four digits, which you can copy from a passport, birth certificate or driver licence.
- Enter your birth month as a number from 1 for January to 12 for December.
- Enter your birth day as the day of the month, from 1 to 31; if that month has fewer days, such as 31 April, the calculator moves it back to the last real day and tells you.
- Press calculate and the results compare your birth date with today's date on your device, so the answer changes each day you come back.
What each result means
- Age
- Your exact age as full years, then full months since your last birthday, then days since the last monthly anniversary. This is the figure forms ask for.
- Next round-number birthday
- The next birthday that ends in a zero, such as 30, 40 or 50, with the date it falls on and how many days away it is, for planning a party or a trip.
- Next 1,000-day milestone
- The next time your total days lived reaches a whole thousand, such as 10,000 or 15,000 days, with the date and how many days are left.
- Total months
- Every complete calendar month you have lived. Handy for infant and toddler ages, which doctors and childcare centres give in months.
- Total weeks
- Total days divided into whole weeks, with the leftover days shown separately so nothing is rounded away.
- Total days
- Every calendar day from your birth date to today, including each 29 February you have lived through. Useful for milestones such as 10,000 days.
- Next birthday in
- Days from today until your next birthday, with the date and weekday it falls on so you can plan around it.
- Age at next birthday
- The age you will turn on that next birthday. Some insurers and schemes price on age next birthday rather than current age.
- Day of the week you were born
- The weekday of your birth date on the Gregorian calendar, worked out from the date itself rather than looked up.
- Birth date used
- The exact date the calculation used. If you typed a day the month does not have, this shows the corrected last day of that month.
The formula
Whole years = the number of full anniversaries of the birth date on or before today
Months = the full months after the last birthday, adding one month at a time
Days = today minus the last monthly anniversary, in days
Total days = (today minus birth date) divided by 86,400,000 milliseconds
Total weeks = total days divided by 7, rounded down
When a month has no matching day, for example 29 February in a common year, the anniversary falls on the last day of that month.
How this number is used in practice
Age cut-offs are strict, and the day matters. Australian school starting ages are set by each state against a birth date cut-off, so a child born one day after the cut-off starts a full year later. Working holiday visas are limited to applicants under a set age on the day they apply, junior sport groups are fixed by age on 1 January or another set date, and retirement and pension ages are reached on a specific birthday.
In each case a person's exact age on a given date is what counts, and whole years alone can hide the fact that someone is a few days either side of the line.
Leap day birthdays are the classic edge case. Someone born on 29 February only has a real birthday one year in four, and legal systems do not agree on which day counts in the other three years. This calculator uses the last day of February, which is how most date libraries and many organisations handle it, but some jurisdictions treat 1 March as the birthday for legal purposes.
If an age threshold falls on or near a leap day birthday, confirm the rule with the agency or insurer involved rather than relying on any calculator.
Insurers and actuaries often talk about age last birthday, age next birthday or age nearest birthday, and the same person can be a different age under each. Life insurance premiums in particular may be set on age next birthday, which is why this calculator shows it separately. When a quote looks higher than expected, check which age basis the insurer used.
Worked examples
Born 15 June 1990 and checked on 1 January 2025
34 years, 6 months and 17 days, which is 414 whole months and 12,619 days lived
Born 25 December 2000 and checked on 10 March 2025
24 years, 2 months and 13 days, with 290 days to go until the 25th birthday
Born 29 February 2004 and checked on 28 February 2025
Exactly 21 years old, because in a common year the birthday falls on 28 February, the last day of that month
Someone entering 31 April 1985
April has 30 days, so the calculator uses 30 April 1985 and says so under Birth date used
When people use it
- Checking exact age for insurance, superannuation, visa or pension applications
- Confirming whether a child meets a school starting age or junior sport age group cut-off
- Giving a baby or toddler's age in months for medical and childcare forms
- Finding the date of a milestone such as 10,000 days alive or a decade birthday
- Working out how many days are left to plan a birthday celebration
Tips
- Copy your date of birth from an official document rather than memory, because forms are checked against those records.
- If a form asks for age next birthday, use that result rather than adding one to your current age in your head.
- For a child near a school or sport cut-off, check the exact cut-off date published by the state or club, then compare dates rather than ages.
- The answer changes at midnight on your device, so check the date on your phone or computer if the result looks a day out.
- If you were born on 29 February, confirm how the organisation you are dealing with treats your birthday in common years.
- Ten thousand days is about 27 years and 4 months, a milestone some people like to celebrate.
What it assumes, and where it stops being accurate
- Today's date is read from your device clock and calendar, so a wrong device date gives a wrong age.
- All dates use the Gregorian calendar, including dates before a country adopted it, so very old historical dates may differ from records of the time.
- Time of birth and time zone are ignored. Age changes at midnight on the birthday rather than at the hour you were born.
- Birthdays on the 29th, 30th or 31st fall on the last day of shorter months, and 29 February birthdays fall on 28 February in common years.
- Birth years from 1900 to 2100 are accepted. Dates after today produce a message rather than a negative age.
Terms used on this page
- Age last birthday
- Your age in completed years, the number most people give when asked how old they are.
- Age next birthday
- The age you will turn on your next birthday, used by some insurers to price cover.
- Leap year
- A year with 366 days. Divisible by 4, except century years not divisible by 400.
- Leapling
- Someone born on 29 February, whose exact birthday occurs only in leap years.
- UTC
- Coordinated Universal Time, a time standard with no daylight saving, used here so every day is exactly 24 hours.
Questions people ask
- How does the calculator count the days part of my age?
- It finds your last birthday, then counts forward whole months, then counts the days left over to today. If you were born on the 31st and a month is shorter, that month's anniversary falls on its last day, so the count never skips or double counts a day.
- Does it account for leap years?
- Yes. Every calculation runs on real calendar dates, so each 29 February you have lived through is included in total days and total weeks. The dates are compared at midnight UTC, which stops daylight saving changes from adding or removing an hour and nudging the day count.
- What happens if I was born on 29 February?
- In leap years your birthday is 29 February as normal. In common years this calculator treats 28 February as your birthday, which is how most date software works. Some legal systems use 1 March instead, so check the rule with the organisation if an age limit is involved.
- What if I type a date that does not exist?
- Days that a month does not have, such as 31 April or 30 February, are moved back to the last real day of that month. The Birth date used result shows the corrected date and explains the change, so you can see exactly what was calculated.
- Why does my age show a different number of days to another website?
- Sites differ in how they borrow days from the previous month and in whether they use your local time or UTC. Years and months should always agree. A difference of one or two days usually comes from those conventions or from a different time zone around midnight.
- Why is the answer different when I come back tomorrow?
- Because the calculator compares your birth date with today's date each time the page loads. Your age in days goes up by one every day, and the countdown to your next birthday goes down by one. That is also why the examples describe fixed dates rather than today.
Use this with
Age Calculator answers one part of the question. These pick up where it stops: Date Calculator, Days Until Calculator, Retirement Savings Calculator and Dog Age Calculator.
Where these figures come from
This calculation is jurisdiction-neutral arithmetic. No country-specific rules are applied.
- Australian Bureau of Statistics: Age standard. How age is defined and calculated for official statistics
- Time and Date: Leap years. Gregorian leap year rules used for day counts
- NIST: A walk through time. History of the Gregorian calendar and civil timekeeping
Age Calculator produces an estimate for general information. It is not financial, tax, medical, legal or engineering advice. read the full disclaimer. Spotted a wrong number? Report it and it gets fixed. The form picks up this calculator and the inputs you used.