Albert Einstein was born on March 14. Johnny Depp’s birthday is the June 9. Taylor Swift’s is on December 13.

Everyone’s got a birthday. Every year on that special day, we get together to celebrate the day we were born. Here are some interesting facts about birthdays:

1. Most popular month

Chances are you know a lot of people with a birthday in September. That’s because September is the most popular birthday month. It is followed closely by July and August. The least common month is January. For some reason summer babies just outnumber winter babies.

2. First birthday invitation

Birthday invitations have been around for a long time. The very first known birthday invitation was sent out during the 1st century. It was sent by Claudia Severa, a Roman commander’s wife, to her sister.

3. Largest birthday cake

In 2005, in honor of Las Vegas’s 100th anniversary, 600 volunteers created a 130,000 pound birthday cake. It was 102 feet long, 52 feet wide and 20 inches tall. It beat the previous record of 128,238 pounds.

4. Birthday Paradox

This paradox states that in a room of 23 people, there is a 50 percent chance that two of them will have the same birthday. That percent hits 99.9 in a room of 70 people.

5. Most expensive birth certificate

In 1997, Paul McCartney’s birth certificate was auctioned for off $84,146. It was sold at an international auction in Tokyo along with other Beatles memorabilia.