Only coming round every four years, the extra day is their true celebration.

The 366th day is added to keep the calendar year synchronised with the astronomical year or seasonal year.

Many of those born on the bonus day, have their own way of marking the occasion on those years in between.

And it can be quite the mind-boggler getting your head around the maths of it all.

We asked leap year babies and parents to share some of their stories and celebrations...

Leah Kirkham, from Buckley: "I love having a quirky birthday, it always tickles me when people don't understand how it works.

"It's my 12th leap year birthday this year and I always throw an epic leap year party for myself, I like to collect for charity on the night.

"This year I'm having a super heroes and super villains themed party and we will be raising funds for Macmillan."

Leap year baby Cheryl Gaulton, pictured as a youngster with her favourite Mickey Mouse toy.

Cheryl Gaulton, from Connah's Quay: "I was born at 00.05 on February 29, 1980, the first baby at the Countess of Chester born that day.

"My hubby says my leap year birthday is like a week-long festival .

"When there's no leap year I celebrate on March 1. This year I'm '11', the same age as my youngest son."

Celebrating one of her official birthdays, Hannah and mum Lynne Chick.

Lynne Chick, from Flintshire: "My daughter Hannah was a leap year baby, she usually celebrates her birthday on February 28, unless of course it's a leap year. She's 36 this year."

Lindsay Davies: "I will be nine this year. My daughter is older than me and before I know it my son will be too. On the plus side, I get to celebrate my 18th and 21st again."

Nicole Jayne Robertson: "My mum Tina Davies she will be 14 this year."

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Vanessa MacDougall: "My husband will be 15 this year (60). We're going up to Scotland to celebrate."

Laura Sharp: "My daughter is 12 this year. We usually celebrate on the 28th, so it will be nice to celebrate on the actual day again this year."

Jaci Louise: "I was born on a leap year and I will be 12 (48) this year."

Jacqui Bowring: "Lexus Bowring is six this year, 24 really, and my boy, my best friend in the whole world. Gorgeous inside and out, so grateful for my leap year baby boy."

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Julie Leathwaite: "My daughter will be eight on leap year day, but 32 in real years (February 29, 1992). She will celebrate her 32nd on February 28 and her eighth birthday on February 29."

For some, it was close but they started the celebrations early - Jan Swinson: "My daughter was due on that date but arrived eight weeks early on New Year's Day."

And of course it's not only birthdays - Elle Gaskell: "Not a leap year baby, but a leap year bride! This year will be out 'first wedding anniversary' in four years."