How does the birthday calculator work?

It compares your date of birth with a selected reference date, finds the next occurrence of your birthday, then calculates the days remaining and age on that birthday.

Can it handle leap-day birthdays?

Yes. For 29 February birthdays, you can choose whether non-leap-year birthday countdowns use 28 February or 1 March.

Time & Dates

Birthday Calculator

Find your next birthday, the day of the week you were born, your age on your next birthday and how many days are left to celebrate.

UK date friendly Leap-day options Instant result

Birthday calculator

Enter a date of birth and choose the date you want to count from. The calculator works in local calendar days.

Date of birth Use the calendar picker or enter YYYY-MM-DD.

Count from Defaults to today.

For 29 February birthdays in non-leap years Different families, forms and organisations may treat leap-day birthdays differently.

UK note: written dates such as 04/05/2026 can be ambiguous internationally. This calculator uses the date selected in the input field.

Next birthday

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Enter your date of birth to see your next birthday.

Days until birthday—

Age on next birthday—

Day of week born—

Birthday this year—

Next milestone—

Exact age today—

Birthday countdowns are based on calendar dates, not legal age rules or eligibility checks.

How the birthday calculator works

The calculator compares your date of birth with a selected reference date. It finds the next occurrence of your birth month and day, then counts the calendar days between the reference date and that birthday.

It also shows the weekday you were born, your age on your next birthday and the next common milestone birthday.

Birthday formula

The logic is simple, but leap-day birthdays and dates that have already passed this year need careful handling.

next birthday = birth month/day in the reference year
if next birthday is before the reference date:
  next birthday = birth month/day in the following year

days until birthday = next birthday - reference date
age on next birthday = next birthday year - birth year

Leap-day birthdays

If you were born on 29 February, your birthday only appears on the calendar in leap years. In non-leap years, some people use 28 February and others use 1 March for countdown purposes.

This calculator lets you choose either approach. For legal, school, work or eligibility purposes, check the exact rule used by the relevant organisation.

Birthday examples

Birthday later this yearIf your birthday is 1 December and today is 20 June, the calculator counts forward to 1 December this year.

Birthday already passedIf your birthday was 1 January and today is 20 June, the next birthday is 1 January next year.

Birthday todayIf the reference date matches your birthday, the calculator shows the birthday as today and days remaining as zero.

Useful time and date terms

Leap year Calendar day ISO week

Birthday calculator FAQs

What day of the week was I born?

Enter your date of birth and the calculator shows the weekday for that exact calendar date.

Does the calculator count today?

For birthdays, the result is a countdown from the selected reference date to your next birthday. If your birthday is today, the countdown is zero days.

Can this prove legal age?

No. This is a practical calculator for dates and birthdays. For legal eligibility, identification, employment, travel or official checks, use the rule set required by the relevant organisation.

Need another date calculation?

Use the Time & Dates hub to find age, working-day, countdown, time-zone and notice-period calculators.

View Time & Dates tools Try Age Calculator

Calculator results are estimates based on the dates you enter.