Age Calculator

What is the Age Calculator?

An age calculator works out your exact age in years, months and days from a date of birth, along with your total days lived and days remaining until your next birthday. It works by comparing today's date to the date of birth, subtracting year, month and day components separately and borrowing from the next-largest unit when a component would otherwise be negative — for example, if today's day-of-month is earlier than the birth day-of-month, it borrows a month and adds that month's day count. To calculate your age manually: subtract birth year from current year, then adjust down by one if your birthday hasn't happened yet this calendar year — total days lived is simply the number of days between the two dates.

How it works

Calculating exact age sounds simple but trips up manual maths surprisingly often, because months have different lengths and leap years add an extra day roughly every four years. An accurate age calculation counts full years elapsed, then the remaining full months, then the remaining days — properly accounting for varying month lengths and leap years — rather than just subtracting birth year from the current year, which can be off by one around a birthday.

UK context

Exact age in years, months and days is useful for far more than curiosity — it's commonly needed for age-restricted eligibility checks, legal and administrative purposes, and working out precise milestones.

Tips

• Simply subtracting birth year from current year gives the wrong answer if the birthday hasn't happened yet this year — always account for whether the birthday has passed.
• Leap years mean some age calculations that span a 29 February need slightly different handling — an accurate calculator accounts for this automatically.

A quick note

This page explains how exact age is calculated from a birth date, accounting for varying month lengths and leap years.