Two sisters. Two holidays. Half a million to one odds.

Some families measure time in milestones. This family measures it in once in a lifetime dates.

Two years ago, Brittany and Josh Young welcomed their first daughter, Janae, at CentraCare - St. Cloud Hospital on one of the rarest days on the calendar, Leap Day. A day that only comes once every four years, giving her odds of about one in 1,461 of being born on Feb. 29. From the start, her birthday was extraordinary.

Josh said, "When we realized Janae would be born on Leap Day, we thought it would be a really fun story, an answer to every 'tell me a fun fact about yourself' ice breaker question."

This year, her little sister, Marlowe, joined the family at the same hospital on a day already devoted to celebrating moms everywhere, Mother's Day. With roughly a 1 in 365 chance of being born on that day, she arrived like the sweetest gift.

"Brittany giving birth to Marlowe on Mother's Day … I can't stop thinking how special that sounds. Nothing more motherly than birthing a child," said Josh.

Here's where the math makes the magic even bigger: The odds of having one child born on Leap Day and another born on Mother's Day are about 1 in 533,000.

And because Leap Day only shows up every four years, the story takes another heart-melting turn. The younger sister will celebrate her first birthday before her older sister ever celebrates her "first" Leap Day birthday.

Two sisters. Two holidays. Half a million to one odds.

Sometimes the calendar just lines up. And sometimes, it tells a story this rare.