Everyday Tools
Age Calculator
Enter a birth date to see the exact age today and how many days remain until the next birthday.
Calculation inputs
Leave the 'as of' date blank to use today.
Results
No result yet
Complete the fields and select Calculate to show results here.
About this calculator
An age calculator works out exactly how old someone is in years, months, and days from a date of birth, and how many days remain until their next birthday. It is useful for forms, eligibility checks, and simple curiosity about milestones.
How the calculation works
- Years, months, and days are counted calendar-style, borrowing days from the previous month when needed
- Days until the next birthday = next anniversary of the birth date − the 'as of' date
Notes and assumptions
Leap days are handled by the calendar itself; a 29 February birthday rolls to 1 March in common years.
How it works in plain English
The calculator compares a birth date with a reference date, which defaults to today unless another 'as of' date is entered. It counts whole years first, then works out the leftover months and days by comparing the month and day components of the two dates.
When the day of the month in the reference date is earlier than the birth day, the calculation borrows a month and adds the number of days in the previous calendar month, since months vary in length. A similar adjustment happens with years if the month count goes negative, keeping the years, months, and days figures consistent with how people naturally describe age.
Alongside the exact age, the tool finds the next occurrence of the birth month and day after the reference date and counts the days remaining until then. If the birthday already passed this year, it looks ahead to next year's date instead.
Worked example
Someone born on June 15, 1990, checking their age on today's date, would first see how many full years have passed since 1990, then the remaining months and days beyond the last full year. If today were March 10, 2024, the birthday for this year (June 15, 2024) hasn't happened yet, so the calculator counts forward to that date and reports the days remaining, while the age itself is based on the most recent birthday, June 15, 2023. That means the exact age reported combines the completed years since 1990 with the extra 8 months and 24 days accrued since the June 2023 birthday through March 10, 2024. Once June 15, 2024 arrives, the years count increases by one and the months and days reset to zero, starting the cycle over for the following year.
Frequently asked questions
How is age calculated with leap years?
The calculator counts actual calendar days and months rather than assuming every year has 365 days, so leap years are naturally absorbed into the day and month totals. Someone born on February 29 will have their age measured against the real calendar, including leap years.
What happens if I enter a future date of birth?
The tool flags this as invalid, since a birth date cannot come after the date you are measuring age against. Double-check that both dates are entered correctly and in the right order. This safeguard catches simple typos, such as swapping a birth year with the current year, before they produce a nonsensical negative age. If you actually need to calculate a future projected age, use the 'as of' date field to move the reference date forward instead of changing the birth date.
Can I calculate someone's age on a date other than today?
Yes, entering an 'as of' date lets you find how old someone was, or will be, on any specific date, which is useful for eligibility rules tied to a cutoff date rather than the current day.
Why do total days and the years/months/days breakdown look inconsistent?
Total days is a straight count of every day between the two dates, while the years/months/days format accounts for how many days are in each specific month passed through, so the two representations of the same span won't convert evenly using a flat 30-day month.
Does the calculator account for time zones?
No, dates are treated as whole calendar days without a time-of-day or time zone component, which is accurate enough for virtually all everyday age questions. Age in years, months, and days depends only on calendar date boundaries rather than the exact hour someone was born, so shifting time zones would not change the reported figures. This approach keeps results simple and consistent no matter where the calculation is performed.