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Age Calculator

Calculate your exact age in years, months, and days, and see how long until your next birthday.

Enter the date you were born

Defaults to today — change to find age at any past or future date

About age calculator

How it works

The calculator counts complete years first, then remaining complete months, then the leftover days. It uses your browser's clock for "today" but you can change the "as of" date to calculate age at any point in the past or future.

Formula

years=⌊(asOf−dob)years⌋months=⌊(asOf−(dob+years))months⌋days=⌊(asOf−(dob+years+months))days⌋\begin{aligned} \text{years} &= \left\lfloor (\text{asOf} - \text{dob})_{\text{years}} \right\rfloor \\ \text{months} &= \left\lfloor (\text{asOf} - (\text{dob} + \text{years}))_{\text{months}} \right\rfloor \\ \text{days} &= \left\lfloor (\text{asOf} - (\text{dob} + \text{years} + \text{months}))_{\text{days}} \right\rfloor \end{aligned}totalDays=⌊asOf−dob86400 s⌋weeks=⌊totalDays7⌋\text{totalDays} = \left\lfloor \frac{\text{asOf} - \text{dob}}{86400\,\text{s}} \right\rfloor \qquad \text{weeks} = \left\lfloor \frac{\text{totalDays}}{7} \right\rfloor

When to use it

  • Checking legal age requirements (driving, voting, alcohol, retirement)
  • Medical forms that ask for age in years and months
  • Birthday countdowns and milestone planning
  • Calculating age at a specific past date (e.g. "How old was I when X happened?")
  • Parenting apps — developmental milestones are often tracked in months

Leap years & edge cases

The calculation handles leap years automatically. If you were born on 29 February, your "official" birthday on non-leap years is treated as 1 March for the purpose of counting complete years.