Birthday Calculator

The birthday calculator turns your date of birth into two things at once: your exact age today, and a countdown to your next birthday. Enter the day you were born and it shows how old you are in years, months, and days, then tells you how many days remain until you next celebrate and which weekday that will be.

It is the natural tool for the two questions everyone asks around a birthday — "how old am I right now?" and "how long until my birthday?". Parents use it to track a child's age and plan the next party; anyone organising a celebration can see exactly which day of the week the birthday lands on this year, which is what decides whether it falls on a weekend.

The age part follows the same month-clamped convention as a full age calculation, so it stays correct across month ends and leap years. Leap-day birthdays are handled sensibly: someone born on 29 February has their birthday recognised on 28 February in common years, and on the leap day itself when one comes round. If today is your birthday, the calculator says so and tells you the age you are turning.

To use it, choose your date of birth and press Calculate. Your age and next-birthday countdown appear instantly, computed privately in your browser. The age calculator gives the fullest breakdown of your age in years, months, weeks, and days.

The calculator measures the completed years, months, and days from your date of birth to today using month-clamped anchoring, then rolls your birthday forward to its next yearly occurrence to find the date, weekday, and days remaining. Leap-day birthdays fall back to 28 February in non-leap years.