Age Calculator

The age calculator works out your exact age from your date of birth: full years, months and days as of today, the day of the week you were born, how many days and weeks you have lived and how many are left until your next birthday. A second mode finds the difference between any two dates. The calculation is strictly calendar-based: months and days are borrowed from neighboring months rather than rounded to a conventional thirty days.

How to use the calculator

Pick the "Age" mode and enter your date of birth – the result appears instantly. The panel shows your age in large type (years, months, days), the day of the week you were born, the total number of days and weeks lived, and a countdown to your next birthday. The "Difference between dates" mode measures the full interval between any two dates: for example, how long a project has been running or how many days are left until your vacation. The order of the dates does not matter – the calculator works out which one is earlier.

If you were born on February 29

For people born on a leap day, the question of when to celebrate is answered differently around the world. This calculator assumes that in non-leap years the birthday falls on February 28 – the most common approach in legal practice: in the legislation of many countries a deadline that lands on a non-existent date is considered the last day of the month. Legal age (voting, retirement, coming of age) is counted from the actual birth date and arrives on March 1.

How age is calculated

Age is calculated by calendar rules. Today's date minus the birth date: days are subtracted first, and if there are not enough, they are borrowed from the previous month (which may have 28, 29, 30 or 31 days); the same happens with months, borrowed from the year. That is why from January 31 to February 28 there are exactly 28 days, not "one month minus three days". The total number of days is simply the difference in days, and weeks are the whole-number part of dividing by seven.

Why exact age matters

Years and months matter in medicine: child growth and weight norms, drug dosages and vaccination schedules are all counted in full months. Documents often ask for age "in full years", and for babies – "in months". An exact difference between dates is needed for work experience, contract terms, pregnancy by weeks, warranty periods and deadlines. Some services count a month as a flat 30 days, which produces 1–3 day errors at month boundaries – this calculator uses the strict calendar method, the same one used in official documents.

This calculator is for information only. Legally significant age and deadlines are defined by the law of your country.