Age & birthday calculator.

How to calculate age from your date of birth

An age calculator compares a date of birth with another calendar date. The familiar result—years, months and days—describes completed calendar anniversaries. It answers a different question from “how many days have passed?” Both views are useful, and Daywise shows them together so you can see the difference.

You can use the calculator for your own birthday, a family milestone or an event anniversary. The start date does not have to be a person's birthday. Choose any valid date and a calculation date on or after it to explore the time between them.

What years, months and days mean

Completed years tell you how many annual anniversaries have passed. The months and days describe what remains after those completed years. Someone born on 15 July 2000 reaches their 25th birthday on 15 July 2025. On the day before that anniversary, they are still 24 years old, even though rounding their age might suggest 25.

That is why subtracting one year number from another is not enough. A calculator also needs to compare the month and day. Similarly, dividing a number of days by 365 gives an approximation rather than a calendar age: some years contain 366 days, and months range from 28 to 31 days.

How Daywise handles the calendar

Daywise uses the Gregorian calendar. It first finds the largest number of complete months between your birth date and the calculation date. It then splits those complete months into years and remaining months. Finally, it counts the calendar days from that monthly anniversary to your chosen date.

There is one detail that matters at the end of a month. If the original day does not exist in the target month, Daywise uses that month's last valid day. For example, one month after 31 January 2023 is 28 February 2023. On 1 March, the result is one month and one day. Every anniversary is calculated from the original date, so a February adjustment does not permanently move later anniversaries to the 28th.

This is an explicit calculation convention. Another calculator may choose a different convention and produce a different breakdown near month ends. The total number of calendar days between the same two dates should still agree. When a date matters for an official application, check the organization's stated age rules.

Leap years and 29 February birthdays

A Gregorian year is a leap year if it is divisible by four, except that a century year must also be divisible by 400. This means 2000 was a leap year, while 1900 and 2100 are not. The extra day is 29 February.

For a person born on 29 February, a birthday countdown needs a choice in years without that date. Daywise lets you choose 28 February or 1 March as the celebration date. This preference changes the next-birthday countdown; it does not change the calendar-age method. Calendar anniversaries continue to use the last valid day of the relevant month.

Neither celebration choice is a universal rule for legal age. A personal birthday tradition, a school deadline and a jurisdiction's legal rule may use different definitions. Use the displayed convention to understand the result, and verify any rule that an institution requires.

Understanding total days, weeks and seconds

Total days count the difference between the two calendar dates. The birth date itself is the starting point, so the result is zero days when both inputs are the same. A calculation date one day later gives one day. Full weeks are obtained by dividing this total by seven, with leftover days shown separately.

The hours and seconds cards are equivalents: one calendar day is treated as 24 hours, and each hour as 3,600 seconds. They do not measure the exact elapsed time since the moment of birth. Without a birth time and time zone, an exact time-of-day calculation is not possible. Daylight-saving changes can also make a local day shorter or longer than 24 hours.

The optional everyday-rhythms feature follows the same principle. It multiplies a chosen per-minute rate by the date-based minutes total. A constant rate cannot describe a person's lifetime heartbeats or breaths, so these numbers are illustrations for curiosity, not personal health information.

Why choose a calculation date other than today?

A reference date lets you answer questions such as “How old was I when I graduated?” or “How old will my child be on the first day of school?” It can also help you plan an anniversary or compare milestones. The calculator defaults to your device's local date, and the Use today button restores that date whenever you need it.

For school, employment or other eligibility decisions, enter the exact cutoff date stated in the relevant instructions. Daywise can show the date difference, but it does not determine eligibility. An application might require completed years only or specify its own treatment of leap-day birthdays.

Check the day, month and year before calculating. Daywise rejects impossible dates, such as 31 April, instead of silently changing them to another month. It also rejects a calculation date that falls before the birth date. These checks help prevent a plausible-looking answer from incorrect inputs.

Keeping your date of birth private

The calculator runs in your browser. Entering dates and calculating a result does not send those dates to a calculator server. The supplied calculator code does not include advertising or analytics. Services you enable in Blogger have their own data practices. A theme preference may be stored on your device, but your entered dates are not saved by the application.

Sharing is a separate choice. A shared link includes the birth date, calculation date and leap-day preference in the part of the URL after the hash symbol. Anyone with the complete link can read those values. Avoid posting the link publicly if you want to keep your birth date private. Copied reports and printed PDFs also include the dates, so treat them as personal information.

For a quick check, the result cards may be all you need. For a record, use Print / Save PDF and choose your browser's PDF destination. The report includes the dates and calculation convention, making it easier to understand the result later.