# How many days until my birthday? Counts the days to your next birthday and gives its date, the age you turn, the day of the week you were born, and your age and days lived so far. - Page: https://www.acalculator.org/days/birthday-calculator - JSON spec: https://www.acalculator.org/days/birthday-calculator.json - Version: 51fc007bdd10 ## Default answer Example with the default inputs (Date of birth June 15, 1995, Count from September 29, 2026) on the example date Tuesday, September 29, 2026: Your next birthday is Tuesday, June 15, 2027 (259 days to go), when you turn 32. ## Inputs | Key | Label | Description | | --- | --- | --- | | birth | Date of birth | Your birthday, with the year you were born. | | on | Count from | The date to count from. Today, unless you change it. | ## Outputs | Key | Label | Description | | --- | --- | --- | | days | Days until your birthday | Days from the count-from date to the next birthday; 0 when the birthday is that day. | | next | Next birthday | The date of the next birthday on or after the count-from date, with its weekday. | | countdown | Countdown | The days to the next birthday in words: “today”, “1 day to go”, or “N days to go”. | | turning | Age on that birthday | The age in whole years reached on the next birthday. | | bornOn | Day you were born | The day of the week of the date of birth. | | age | Age now | The age on the count-from date in whole years, months, and days. | | daysLived | Days lived | Days from the date of birth to the count-from date. | ## Method next birthday = the date of birth plus the fewest whole years (at least 1) that is on or after the count-from date; days until = next birthday − count-from date. ## Assumptions - The next birthday is the first birthday on or after the count-from date, so on your birthday the count is 0. - A February 29 birthday falls on February 28 in years that are not leap years. - Dates are calendar days on the Gregorian calendar (1600 to 2400), with no time of day or time zone. - Age is whole years, then whole months, then days; month ends clamp (January 31 plus one month is February 28 or 29). - A date of birth after the count-from date gives no answer. ## Worked examples 1. birth = 1995-06-15, on = 2026-09-27 gives countdown = 261 days to go, days = 261, next = 2027-06-15, turning = 32, bornOn = Thursday, age = {"years":31,"months":3,"days":12}, daysLived = 11,427. Source: hand calculation in content.mdx; Python: (date(2027,6,15) - date(2026,9,27)).days = 261. 2. birth = 2000-02-29, on = 2026-09-27 gives days = 154, countdown = 154 days to go, next = 2027-02-28, turning = 27, bornOn = Tuesday. Source: hand calculation in content.mdx; Python: (date(2027,2,28) - date(2026,9,27)).days = 154. 3. birth = 1990-09-27, on = 2026-09-27 gives days = 0, countdown = today, next = 2026-09-27, turning = 36, age = {"years":36,"months":0,"days":0}. Source: hand calculation in content.mdx: 2026 − 1990 = 36. 4. birth = 2026-09-27, on = 2026-09-27 gives days = 365, countdown = 365 days to go, next = 2027-09-27, turning = 1, daysLived = 0. Source: hand calculation in content.mdx: September 27, 2026 to September 27, 2027 is 365 days. 5. birth = 1969-07-20, on = 2026-12-31 gives countdown = 201 days to go, days = 201, next = 2027-07-20, turning = 58, bornOn = Sunday. Source: hand calculation in content.mdx; July 20, 1969 (the Apollo 11 Moon landing) was a Sunday; Python: date(1969,7,20).weekday() = 6 (Sunday). ## FAQ ### How many days until my birthday? Count the days from today to your next birthday. For a June 15 birthday, counted from September 27, 2026: 3 days left in September, then 31 + 30 + 31 + 31 + 28 + 31 + 30 + 31 days to May 31, then 15 days of June, for 261 days. The calculator counts from today unless you pick another date. ### What day of the week was I born? The page shows it under "Day you were born". It counts the days from a date with a known weekday; for example July 20, 1969, the day of the Apollo 11 Moon landing, was a Sunday. ### When is my birthday if I was born on February 29? In a leap year, on February 29. In other years this calculator uses February 28, the last day of February. Some places use March 1 for legal purposes, so check if it matters for a document. ### How is my age worked out? Whole years first, then whole months, then days. Born June 15, 1995, on September 27, 2026 you are 31 years, 3 months, and 12 days old: 31 years to June 15, 2026, 3 months to September 15, and 12 more days. ### What does it show on my birthday? 0 days: the birthday is today, and the age shown is the age you turn today. ### Which leap years does it count? The Gregorian rule: a year divisible by 4 is a leap year, except years divisible by 100, which are leap years only if they are also divisible by 400. So 2000 was a leap year and 1900 was not. ## Sources - U.S. Naval Observatory, Leap Years: the Gregorian leap year rule. https://aa.usno.navy.mil/faq/leap_years - NASA, Apollo 11 Mission Overview: landed on the Moon on July 20, 1969. https://www.nasa.gov/mission/apollo-11/