Golden Birthday Calculator

DateMath takes the day of the month you were born as the golden age and adds that many years to your date of birth: born on June 12, 2010, the golden birthday is June 12, 2022, at 12. The double golden birthday adds twice as many years. The Beddian birthday adds the last two digits of the birth year, so it doesn't exist for years ending in 00. A February 29 birthday falls on February 28 in common years, as in the age calculator.

• The Gregorian calendar. DateMath treats every date as a Gregorian date, with its leap-year rule: a year divisible by 4 is a leap year, except century years not divisible by 400, so 2000 had a February 29 and 2100 will not. Source: Gregorian calendar.

DateMath's date math is tested against more than 100 cases worked out by hand. Every worked example and table on the site is computed with the same code the calculators run, so a page and its calculator can't disagree.

Your golden birthday is the birthday when your age matches the day of the month you were born: born on the 12th, you have it at 12. It comes once, between the 1st and the 31st birthday. The golden birthday calculator gives its date and weekday and says whether it has passed, along with the other special birthdays people look up.

The method, step by step

Born June 12, 2010:

1. Take the day of the month: 12. That is the golden age.
2. Add it to the birth year: 2010 + 12 = 2022, so the golden birthday is Sunday, June 12, 2022.
3. Double it for the double golden birthday: 24, on June 12, 2034.
4. Take the last two digits of the birth year for the Beddian birthday: 10, on June 12, 2020.

The golden age is simply the day of the month, so a child born on the 1st has it on the first birthday and one born on the 31st at 31. The year is the birth year plus that age; for a birth in 2015:

The Beddian birthday is the birthday when your age equals the last two digits of your birth year, named in tribute to firefighter Bobby Beddia, as Wikipedia’s Birthday article notes. The same day is also called a platinum birthday or a diamond birthday, so a platinum birthday calculator or a diamond birthday calculator usually means this one. Years ending in 00 have none, and births early in a century get theirs very young:

The older meaning of diamond and platinum is the 60th and the 70th birthday, after the diamond and platinum jubilees. DateMath gives both, so whichever one a card or a party means, its date is in the result.

For a date of birth of June 12, 2010, compared with January 1, 2027:

A February 29 birthday falls on February 28 in common years, the rule the age calculator uses. Born February 29, 1996, the golden birthday at 29 is February 28, 2025 (Friday), passed 1 year ago, because a leap year plus 29 is never a leap year. The Beddian birthday, at 96, is February 29, 2092 (Friday), in 23,800 days: a leap year’s last two digits are a multiple of 4, so it always lands on a real February 29. The leap year calculator counts the real birthdays in between.

Born on the 29th, 30th or 31st, the golden birthday is still your birthday, in the year you turn that age; nothing moves, because the birthday itself has that day.

• Count down to it. Enter the date in the day countdown to see the days, hours and minutes left.
• Pick the party day. The result gives the weekday, so you can see whether it falls on a weekend.
• Other birthdays to mark. The half birthday calculator gives the day 6 months after the birthday, and the Hebrew birthday calculator the birthday in the Jewish calendar.