For most people, their date of birth is an immutable fact, one not subject to caveats or misunderstanding.

But being born on Feb. 29 means living with a permanent asterisk hovering over an anniversary most take for granted. For Leap Year babies, whose true birth date only comes around every four years, even the question of their age requires a bit of mental calculating.

“As a little kid, we celebrated my birthday on Feb. 28, the same day as my dad’s,” said East Lyme resident Carole Showalter who turned 60 – or 15 – on Thursday. “I didn’t understand for a while why I didn’t have my own birthday.”

As Showalter got older, she gleaned the broad reasoning behind her jumping birthday, though that knowledge didn’t prevent the occasional misunderstanding.

“In Connecticut back in the ‘80s, the drinking age changed from 18 to 21 and it was done one year at a time,” she said. “I’d get accused of having a fake ID at clubs and liquor stores.”

After a few such encounters, Showalter decided she’d had enough.

“I had the guts to ask to speak with a manager at a club and they ended up giving me a VIP pass,” she said.

But there are upsides.

“I’ve been lying about my age for years,” Showalter said. “I can take years off my age, something I didn’t appreciate until I turned 40. But in my heart, I wouldn’t change my birthday; it’s one I got to share with my dad.”

Keeping the calendar synched

Leap Year essentially serves as a calendar version of a software patch, required since the orbital paths of celestial bodies, like the Earth’s around the sun, don’t adhere to our modern calendars, said astrophysicist Chris Faesi, a professor of physics at UConn.

“We define a day as 24 hours, from sunrise to sunrise and, because of human logic, we need a round number of days in a year,” Faesi said. “But it actually takes a little more than 365.24 days for the Earth to orbit the sun. It becomes a rounding issue.”

The extra quarter of a day each year is made up during a Leap Year – most times. Because Earth’s orbital period is actually a tiny bit less than a quarter of a day, Leap Years in certain centuries get skipped, as it was in 1900 and will be again in 2100.

“Even with the current system, we still add just a tiny bit too many days to account for the exact value of Earth’s orbital period,” Faesi said. “As it stands we will have added one too many days every 3,300 years or so. This would imply that 3,300 years from now, the summer and winter solstices would occur one day earlier than they should.”

“Today’s the day”

Wearing a smart-looking button-down shirt and tie, Pawcatuck resident Henry Main comes across as much older than both his actual (12) and calendar (3) ages. He said growing up with an odd birthday carries the occasional pitfalls ― some teasing from classmates when he was younger ― but also a certain cachet.

“People ask me questions and it’s an opportunity to inform them about Leap Year,” he said. “A lot of my friends think it’s cool to not have a normal calendar birthday.”

Henry’s mom, Sara Main, wasn’t expecting a Leap Year birth.

“Henry was five days late and I was hoping he’d come before or after Feb. 29,” she said. “But, during an unusual snowy day in an Oregon hospital, I was told ‘today’s the day.’”

As he got older, Henry, a sixth-grader at Stonington Middle School, decided to educate himself on his birth date by leafing through books and peppering a school librarian with questions.

This year, Henry, an aspiring pilot who’ll help teach math to younger students this year, has a jam-packed birthday in front of him.

“We’ll go to breakfast and I’ll drop him off at school for a few hours before we go out to lunch,” Sara Main said. “Later this week, Henry and eight of his friends go out to the Great Wolf Lodge (water park).”

In reporting this story, The Day solicited comments from Leap Year babies from across the region. Here are some of their experiences:

“I’ve had people tell me there’s no Feb. 29 date and that my driver’s license is wrong.” Gales Ferry resident Jessica Schend, age 56 and 14.

“When I went to DMV to get my license in 2000, the system didn’t recognize Feb. 29 as my birthday, so I had to get a managerial override. I double-dip most years by having cake on Feb. 28 and going out with friends on March 1.” Groton resident Josh Geyer, age 40 and 10.

“The coolest part of my birthday this year is that my daughter turned 8 this month as well. She was actually due on leap year, but came early. My great-grandmother was a leap year birthday, too. I guess it runs in the family.” Groton resident Nicole Depot, age 32 and 8.

j.penney@theday.com