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Born in 1916, Daisy Belle Ward is celebrating her 25th birthday – and that isn’t a math error.

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Ward is America’s oldest-living “leap baby.” She was born on Feb. 29, 1916, which means she has only had 25 calendar birthdays, but has lived 100 years.

Ward, who usually celebrates the rare occasion with a dinner amongst family and friends, went all out this year for the quarter-century/centennial bash, reports CBS News. The birthday girl donned her Sunday best for the extravagant party, which included an 80-piece marching band.

What in the world led to Leap Day and this unusual birthday situation?

“Mother Nature has a sense of humor. She did not make a simple calendar so that when you go around the sun, it’s 365 days. That’s what we learned in school, right? Oh, no,” theoretical physicist Michio Kaku told CBS News. “Mother Nature made it so that every 365 days plus 5 hours, 49 minutes and a few odd seconds. That means that every year, we have to compensate for one quarter of a day. So after four years, we have to add one more day.”

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Because this adjustment still leaves 11 minutes unaccounted for at the end of each leap year, the rules were eventually changed so years divisible by 100 (1800, 1900, etc.) did not have a leap day, unless (!) the year was also divisible by 400, like 1600 and 2000.