Age Calculator

How to use Age

Type or pick the date of birth. Leave the second date as today, or change it to any other day — past or future. Read the result and switch units if you want the answer in something other than years.

What an age calculator is actually for

Forms are the obvious case — some ask for age in years and completed months, and guessing gets it wrong around birthdays. Less obvious uses: how old you will be on a date in the future, the exact gap between two siblings, or the true age of a contract, a pet, a sourdough starter.

It also works as a converter: one lifespan expressed as years, months, weeks, days and hours. The bigger units flatten detail; the smaller ones inflate it. Same life, five different numbers.

The birthday answer vs. the exact answer

Ask a person their age and you get completed years — the birthday answer. The calculator counts from date to date instead: if the birthday has not yet come this year, that year is not counted, and the remainder shows up as months and days. That is why "34" and "34 years, 11 months, 20 days" can describe the same person and feel like different people.

The other tools on the Date Calculators page work the same way — the plain date calculator for spans between any two dates, the sleep calculator for tonight's arithmetic. Dates in, a number out. Your age in years changes once a year. Your age in days changes every midnight — quote whichever number suits the occasion.

Ages other than your own

The same calculation answers a lot of questions that are not about people: how old a document is, how long a company has existed, how far apart two people are in age, how old someone was on a given historical date. For an age gap, run both birth dates and compare — the gap in days holds steady, while the gap in years appears to change between birthdays.