This is a big day for people born on a leap day, who will finally be able to celebrate their birthday for the first time in four years.

Of course, they’ve aged since 2020, but what was considered to be their legal birthday in the intervening non-leap years?

“You know, I’m not really sure,” said John Reitz, the Edward Carmody Professor of Law Emeritus and an expert in administrative law, the field of law that includes the administration of government. It turns out, he said that the consequences of leap day aren’t the sort of thing that governments or the law really spend much time thinking about.

“I don’t know of any statute or general rule that has anything to do with leap day,” said Reitz, an absence that suggests the issue has never caused any problems significant enough that require attention from legislators or other elected bodies.

“Any laws that are time sensitive define a time period—30 days, 60 days, one year—so any impacts of leap day are covered there,” Reitz said.

But Reitz speculates that March 1 would likely be considered the legal birthday in non-leap years of someone born on leap day. His legal thinking is that February 29 is the day after February 28, so a person born on February 29 is legally considered to have aged one year on the day after February 28. In non-leap years, that day is March 1.

So for someone born on February 29, the first day they can legally drive, vote, join the Army, buy alcohol or start collecting Social Security is presumably March 1 in non-leap years.