Quick answer
The next birthday is the next occurrence of your month and day on or after today's date. For 17 May 1990 and a reference date of 1 March 2025, it falls on Saturday 17 May 2025, in 77 days, when you turn 35.
Enter the date of birth and a reference date. The calculator returns the next birthday, days until it, the age you turn and your current age.
Related tools: Half Birthday Calculator: The date six months after a birthday. Baby Age Calculator: A baby's age in weeks, months and days. Age Difference Calculator: Time between two birth dates.
How to use the Birthday Calculator
- Pick date of birth.
- Pick reference date.
- Press Calculate to see the result, and use Reset to start again.
| Input | What to enter | Allowed values |
|---|---|---|
| Date of birth | A calendar date | — |
| Reference date | A calendar date | — |
Formula and method
Formula
next birthday = the next occurrence of the month and day of birth on or after the reference date
IEEE-754 double precision; shown to the decimals indicated.
A February 29 birthday is counted on February 28 in non-leap years.
Worked examples
These examples are verified: each one is an automated test case that the live calculator must reproduce exactly.
Example 1
Inputs: Date of birth = 1990-05-17; Reference date = 2025-03-01.
| Result | Value |
|---|---|
| Next birthday | 2025-05-17 |
| Days until | 77 |
| Turning | 35 |
| Weekday | Saturday |
| Current age | 34 years, 9 months, 12 days |
Example 2
Inputs: Date of birth = 2000-12-25; Reference date = 2025-12-25.
| Result | Value |
|---|---|
| Next birthday | 2025-12-25 |
| Days until | 0 |
| Turning | 25 |
| Weekday | Thursday |
| Current age | 25 years, 0 months, 0 days |
Example 3
Inputs: Date of birth = 1985-02-10; Reference date = 2025-06-30.
| Result | Value |
|---|---|
| Next birthday | 2026-02-10 |
| Days until | 225 |
| Turning | 41 |
| Weekday | Tuesday |
| Current age | 40 years, 4 months, 20 days |
The first line is the headline result (next birthday). Below it the birthday Calculator lists days until, turning, weekday and current age, which describe the same case from other angles. IEEE-754 double precision; shown to the decimals indicated.
Leap-day birthdays
A person born on 29 February has a birthday only in leap years. Practice varies between 28 February and 1 March in other years; check the rule that matters for the purpose, such as a legal age.
Current age in full
Current age is shown in years, months and days: 34 years, 9 months, 12 days on the reference date. The 'turning' value is the age you reach on the next birthday.
What happens with invalid input
These messages are produced by the calculator itself, so you know what to fix.
- Reference date: entering "2025-01-01" shows "The reference date must not be before the birth date." beside that field and no result.
- Date of birth: left empty shows "Enter date of birth." beside that field and no result.
Choosing between the Birthday Calculator and similar calculators
Each row shows what a related calculator on this site asks for and what it returns, so you can pick the one that matches your question.
| Calculator | You enter | It returns |
|---|---|---|
| [Half Birthday Calculator](/lifestyle/half-birthday/) | date of birth | Half birthday |
| [Baby Age Calculator](/lifestyle/baby-age/) | date of birth and reference date | Age |
| [Age Difference Calculator](/lifestyle/age-difference-calculator/) | first birth date and second birth date | Age difference |
| [School Age Calculator](/lifestyle/school-age/) | date of birth and school cutoff date | Age on the cutoff date |
| [Birth Date from Age Calculator](/lifestyle/age-to-birthday/) | age in years and reference date | Possible birth dates |
Assumptions and limitations
- Birthdays on the reference date show 0 days
If a required value is empty, not a number, or outside its allowed range, the form marks that field with a message and shows no result instead of a misleading number. The automated checks deliberately try invalid entries for reference date and date of birth to confirm this.
Frequently asked questions
How many days until my birthday?
The calculator counts from your reference date; it is 77 in the example.
Does it show the weekday?
Yes, Saturday in the example.
Can I use a past date as the reference?
Yes, to find the next birthday after that date.
What does the Birthday Calculator calculate?
Next birthday, days until it, and your current age. It returns Next birthday, Days until, Turning, Weekday and Current age.
What formula does the Birthday Calculator use?
next birthday = the next occurrence of the month and day of birth on or after the reference date. A February 29 birthday is counted on February 28 in non-leap years.
What do I need to enter in the birthday Calculator?
You enter Date of birth and Reference date.
How is the result rounded or limited?
IEEE-754 double precision; shown to the decimals indicated. Birthdays on the reference date show 0 days.
What is an example of a birthday result?
With date of birth 1990-05-17 and reference date 2025-03-01, the next birthday is 2025-05-17.
Related calculators
- Half Birthday Calculator — The date six months after a birthday.
- Baby Age Calculator — A baby's age in weeks, months and days.
- Age Difference Calculator — Time between two birth dates.
- School Age Calculator — Child's age on a school cutoff date.
- Birth Date from Age Calculator — Range of possible birth dates for someone of a given age.
- Graduation Year by Birthday Calculator — High school graduation year from a birth date and your school's entry rules.
- Weekday Calculator — Look up the weekday (Monday to Sunday) of any past or future date.
Sources
- ISO 8601-1: Date and time, representations for information interchange (calendar dates, ordinal dates and week dates)
- Gregorian calendar reform, papal bull Inter gravissimas (1582): the leap-year rule used for all dates
Content last reviewed 2026-11-04. Formulas and worked examples are checked by automated tests against independently computed values.