Age Calculator
Find an exact age to the day. Enter a date of birth and, optionally, the date you want the age measured on — useful for eligibility cut-offs, forms, and school enrolment dates.
No age calculated yet
Choose a date of birth above. Leave the second field empty to measure the age as of today.
How to Use
- Pick the date of birth using the date field.
- Leave the second field blank to measure the age as of today, or set it to a future or past date to see the age on that specific day.
- Read the exact age in years, months, and days, along with the totals in months, weeks, and days.
- Check the next birthday card for the weekday it falls on and how many days away it is.
Features
- Calendar-accurate age in years, months, and days — not an approximation from a day count
- Optional "as of" date for eligibility and cut-off checks
- Total months, weeks, and days lived
- Days until the next birthday plus the weekday it lands on
- Rejects impossible dates and warns if the target date precedes the birth date
Why Calendar Age Is Harder Than It Looks
The naive way to compute an age is to subtract two timestamps and divide by the number of milliseconds in a year. That gives a decimal that is almost always slightly wrong, because years are not a fixed length: three years in four have 365 days and the fourth has 366. Divide by 365.25 and you drift; divide by 365 and you drift the other way. This calculator instead walks the calendar the way a human would. It subtracts the year, month, and day components separately, then borrows — if the day of the month has not yet come around, it takes the length of the preceding month and reduces the month count by one; if the month count then goes negative, it adds twelve and reduces the year.
That borrowing step is where the month-length problem shows up. Someone born on 31 January is, on 28 February, one month minus three days old in a common year — but on 1 March they cross into one month and one day. Because the borrowed value depends on which month you are borrowing from, the same pair of dates can produce a different "days" component than a rival calculator that always borrows thirty days. Ours borrows the true length of the preceding month, which is the convention almost every legal and administrative system uses.
Exact ages matter more often than people expect. School enrolment usually depends on a child's age on a specific cut-off date rather than today. Insurance premiums and pension milestones step at exact birthdays. Visa and licence eligibility, sports age brackets, and medical dosing charts all key off a precise date. That is what the optional "as of" field is for: rather than mentally projecting an age forward, set the target to the cut-off date and read the answer directly. One caveat worth knowing — for anyone born on 29 February, a birthday exists only in leap years, and this calculator rolls the non-leap-year occurrence to 1 March, which is the most common administrative convention but not a universal one.
Frequently Asked Questions
Does the total days figure include leap days?
Yes. It is a true count of calendar days between the two dates, so every 29 February that fell in between is included. That is why the total will not equal your age in years multiplied by 365.
What happens if I was born on 29 February?
The years, months, and days figures are exact regardless. For the next-birthday card in a non-leap year, the date rolls forward to 1 March, which matches how most registries and licensing bodies treat it. Some jurisdictions use 28 February instead, so check the local rule if it is legally significant.
Can I calculate an age on a future date?
Yes — put the future date in the "as of" field. This is the quickest way to check whether someone will meet an age requirement by a particular deadline.
Which timezone is "today" based on?
Your device's local timezone. All dates are treated as plain calendar dates at local midnight, so no hidden hour offsets can shift the result across a day boundary.
Is my date of birth recorded anywhere?
No. The date stays in the page's memory in your own browser. Nothing is transmitted to a server and nothing is written to storage or cookies.