Example 1
- Date of birth: 1990-06-15
- As of: 2026-08-18
June 15, 2027, 301 days. Birth: Friday. Next: Tuesday.
After 15 June, counting from 18 August 2026, the calculator gives 15 June 2027, which is 301 days.
Birthday calculator
Pick a date of birth and, if you want, an as-of day. The calculator finds the next birthday, the civil days until it, and the weekdays of birth and of that next date. June 15, 1990 on August 18, 2026 is June 15, 2027, 301 days. February 29 in a common year lands on February 28. This is not age in years.
Age in years, months, and days: age calculator. Pregnancy estimate from a period: due date calculator. This page finds the next birthday, not lived years and not 280 pregnancy days.
Result
Date of birth and As of (blank = today on this device). Next birthday shows up here.
How it works
This calculator answers three calendar questions: when the next birthday falls from the as-of date, how many civil days remain, and on which weekday someone was born, plus the weekday of that next birthday. June 15, 1990 on August 18, 2026 gives June 15, 2027 and 301 days. Birth falls on a Friday, the next date on a Tuesday.
You are looking up the next birthday on the calendar. That page counts years, months, and days of life as of today. Here we do not ask how old someone is. We ask for the next calendar anniversary and the day gap. It is also not a due date. A due date shifts the last menstrual period by about 280 days. A birthday takes the month and day of birth and looks for them in the as-of year or the next year.
An empty birth field will not invent a date. An empty as-of field takes today from this device clock. If the as-of month and day fall after the birthday, the next date is in the following year. When as-of lands exactly on the birthday, days until it are zero. A birth date after as-of will not run, because that civil day has not happened yet.
For February 29 in a common year, the next birthday lands on February 28, not March 1. That is a common civil convention, because February 29 does not exist then. In a leap year, February 29 stays February 29. The day gap subtracts calendar days, not hours, so a March clock change does not shrink a weekend in this count.
Saturday and a public holiday enter the same way as Monday. The examples below insert fixed date pairs so the result does not jump after midnight. The metric or US switch converts nothing here, because there are no meters.
Age in years, months, and days lives on the neighbor card. Days until any event, not only a birthday, live on the countdown. A due date stays with about 280 days from a period.
How to use
- Pick a date of birth, for example June 15, 1990. Without that date the calculator has nothing to look up on the calendar.
- Leave the as-of field empty to use today on this device, or type another as-of day, for example August 18, 2026.
- Click Calculate. June 15, 1990 on August 18, 2026 gives June 15, 2027 and 301 days.
- Also read the weekday of birth and the weekday of the next birthday.
- For February 29 in a common year the next date falls on February 28. Age in years lives on the age page.
Formula
next birthday = month and day of birth in the as-of year, or in as-of year + 1 when that day already passed
For 29 February in a non-leap year the day is 28 February. days = civil-day difference from the as-of date to the next birthday. Weekday comes from the date of birth and from the next birthday. Empty birth date or a birth date after the as-of date is an error.
As-of and the next birthday
The next birthday takes the month and day of birth. June 15, 1990 with as-of August 18, 2026 is June 15, 2027, 301 days.
- as-of
- The reference day. Empty takes today. August 18, 2026 with June 15, 1990 gives 301 days to June 15, 2027.
- birthday
- The next anniversary on the calendar, not age. February 29 in a common year lands on February 28, not March 1.
Examples
Example 2
- Date of birth: 2000-02-29
- As of: 2025-03-01
February 28, 2026, 364 days. Birth: Tuesday. Next: Saturday.
29 February after 1 March 2025 gives 28 February 2026, because 2026 is not a leap year.
Example 3
- Date of birth: 2000-02-29
- As of: 2025-02-01
February 28, 2025, 27 days. Birth: Tuesday. Next: Friday.
1 February 2025 in the as-of field, before 28 February, gives 27 days to 28 February in a non-leap year.
Example 4
- Date of birth: 1995-08-18
- As of: 2026-08-18
August 18, 2026, 0 days. Birth: Friday. Next: Tuesday.
The same month and day as the as-of date gives 0 days, because the next birthday is that civil day.
Example 5
- Date of birth: 1995-08-19
- As of: 2026-08-18
August 19, 2026, 1 day. Birth: Saturday. Next: Wednesday.
19 August with 18 August in the as-of field gives 1 day until the next birthday in the same year.
Example 6
- Date of birth: 2001-01-01
- As of: 2026-12-31
January 1, 2027, 1 day. Birth: Monday. Next: Friday.
A 1 January birthday with 31 December 2026 in the as-of field gives 1 day until the next date in the new year.
Example 7
- Date of birth: 1988-12-25
- As of: 2026-08-18
December 25, 2026, 129 days. Birth: Sunday. Next: Friday.
A 25 December birthday with 18 August 2026 in the as-of field gives 129 days until that winter date.
Example 8
- Date of birth: 1964-02-29
- As of: 2028-02-28
February 29, 2028, 1 day. Birth: Saturday. Next: Tuesday.
In leap 2028, 28 February in the as-of field gives the next date 29 February, because that day exists then.
Frequently asked questions
When is the next birthday for June 15, 1990 on August 18, 2026?
June 15, 2027, 301 civil days. Birth is a Friday, and the next date is a Tuesday.
Is that the same result as age in years?
No. Age counts lived years, months, and days, for example 26 years from January 1, 2000. Here we look up the next calendar date and the days until it, such as 301 days to June 15, 2027.
What if I leave as-of empty?
The calculator uses today from this device and counts days to the next birthday. Tomorrow the same birth entry, for example June 15, 1990, will yield a new day count.
Where does February 29 land in a common year?
On February 28, not March 1. February 29, 2000 with as-of March 1, 2025 gives February 28, 2026 and 364 days.
What if as-of lands exactly on the birthday?
Days until it are zero, and the next date is that same day. August 18, 1995 with as-of August 18, 2026 gives 0 days.
Why will a birth date after as-of not run?
That civil day has not happened yet, so we do not count a birthday from the future. June 15, 2030 with as-of August 18, 2026 does not start.
Does Saturday drop out of the day count?
No. Every civil day counts the same, including a holiday. June 15, 1990 on August 18, 2026 is still 301 days, weekends included.
Is this a due date from a period?
No. A due date is about 280 days on a separate card, for example October 8, 2026 from January 1. Here we take the month and day of birth and find them on the calendar.
Why is there a weekday on the page?
So you can see the weekday of birth and the weekday of the next birthday. For June 15, 1990 that is Friday, and June 15, 2027 is Tuesday.
Where are days until a wedding, not a birthday?
On the countdown to a date. There the target is any day, and the start is today. Here the target always repeats the month and day of birth, such as June 15.
Knowledge sources
Day counts and age follow the Gregorian calendar. This is date arithmetic, not a time-zone tool.
Page updated in 2026.