Age Calculator — Years, Months & Days

How the Age Calculator Works

This privacy-first age calculator returns an exact breakdown of age in years, months, and days, a detailed age breakdown in days, weeks, months, hours, minutes, and seconds, a countdown to the next birthday, and your age on any specific date. It runs entirely in your browser, so your dates never leave your device.

What is an age calculator?

An age calculator is a date calculator focused on the question “how old is this person on this date?” Instead of simply subtracting years, it uses calendar rules: months have different lengths, leap years add 29 February, and a birthday may or may not have happened yet in the target year. That matters for forms, school cut-off dates, sports categories, benefit eligibility, HR checks, medical records, and birthday countdowns.

How to calculate age from date of birth

To calculate age from a date of birth, compare the birth date with the target date. First count completed years. If the birthday has not occurred yet in the target year, subtract one year. Then count completed months from the last birthday anchor, and finally count the remaining days. For example, someone born on 15 September 1998 is not simply “2026 minus 1998” on 30 May 2026, because their September birthday has not happened yet. Their completed age is 27 years, 8 months, and 15 days.

Start by selecting your Date of Birth. If you leave the Target Date empty, the calculator uses today’s date, making it a quick “How old am I?” tool. To check an age at a past or future moment—such as a filing date, school start, or compliance cut-off—choose a Target Date and click Calculate Age. The algorithm computes differences in a calendar-aware way: it accounts for varying month lengths (28–31 days) and leap years when rolling through months and years.

Age on a specific date

The target date field lets you calculate age in the past or future. This is useful when the important question is not “how old today?” but “how old on the application deadline?” or “how old at the event date?” Examples include checking whether a child meets a school-year cut-off, whether an athlete fits an age bracket on competition day, whether a person reaches 18 by a contract date, or whether someone reaches retirement age by a benefit start date.

Age in weeks, months, days, hours, minutes, and seconds

The main age result uses calendar units because that is how people normally describe age. The detailed breakdown gives a different view: total days lived, completed weeks, completed months, and the equivalent hours, minutes, and seconds. These totals are based on whole elapsed calendar days from the birth date to the target date. They are ideal for milestone posts, baby age tracking, project-style timelines, and quick conversions such as “how many weeks old is my baby?” or “how many days old am I?”

How old is my child?

For babies and young children, age is often more useful in months and weeks than in years. A child born on 10 June 2021, for example, may be described as 4 years old in everyday conversation, but a school, clinic, or childcare form may need the exact years, months, and days. Use the Child age example chip to load a recent birth date, then adjust it to your child’s real date of birth. For newborn and infant milestone tracking, use the baby age in weeks and months calculator to see age in weeks and months, or the baby age calculator view for total days and calendar months.

Age eligibility examples

Eligibility rules often depend on age on a specific date. If a program requires someone to be 18 by 30 May 2026, enter the birth date and set the target date to 30 May 2026. A person born on 30 May 2008 turns 18 exactly on that date. A person born on 31 May 2008 is still 17 years, 11 months, and 30 days on 30 May 2026. These one-day differences are why exact date-based age calculations are safer than mental math.

Leap year birthday rules: Feb 28 vs Mar 1

When the Target Date is today, you’ll also see time until your next birthday. For birthdays on 29 February, the next birthday in non-leap years is treated as 28 February by default, a widely used convention for anniversary calculations.

Some legal systems, organizations, or family traditions use 1 March instead. There is no single worldwide rule for every situation, so always check the policy that applies to your form or deadline. This tool uses 28 February as the default because it is a common anniversary convention and keeps the next-birthday countdown predictable for leap-day births.

Why results differ between calculators

Age calculators can differ because they choose different conventions. Some count birthday anniversaries on 28 February for leap-day births; others use 1 March. Some include the start day when reporting total days, while others count only completed days after birth. Some show approximate “months” by dividing days by 30.44, while this calculator reports completed calendar months. If a result is being used for legal, school, medical, or benefits eligibility, use the convention required by that organization.

Age calculation examples

DOB: 2000-01-01. On 1 January 2026, the person is exactly 26 years old. The breakdown shows 312 completed months and 9,497 elapsed days.

Leap day: 2004-02-29. In leap years, the birthday is 29 February. In non-leap years, this calculator treats the birthday anniversary as 28 February for countdown purposes.

Age on date: 1998-09-15 to 2026-05-30. This scenario demonstrates why age is not just target year minus birth year. The birthday has not happened yet in 2026, so the exact age is lower than a rough year subtraction suggests.

Typical uses include education and HR onboarding (age eligibility), sports or event categories, visa and immigration paperwork, pension and benefits planning, and milestone tracking. Outputs are presented in clear language and can be copied directly into forms or spreadsheets.

Tip: you can adjust either the Date of Birth or the Target Date and immediately re-run a scenario—handy for “what-if” checks around cut-off dates.

Age Calculator: FAQs

Does this calculator handle leap years and different month lengths?

Yes. The calculator accounts for leap years and varying month lengths when computing years, months, and days.

Can I calculate age on a past or future date?

Yes. Choose a Target Date to see the age on any past or future date instead of today.

Is my data private?

Yes. All calculations run locally in your browser; no data is uploaded or stored on a server.

What happens with birthdays on 29 February?

For non-leap years, the next birthday is treated as 28 February by default (some organisations prefer 1 March).