Why Newton Had Two Birthdays

Wait… how can someone have TWO birthdays? Sir Isaac Newton does—and here’s why.

Newton was born on December 25, 1642… but also on January 4,

1643. Sounds impossible, right? Back then, England used the

Julian calendar, which was 10 days behind the calendar we use today. When the world later

switched to the Gregorian calendar, Newton’s birthday shifted forward—creating two official dates.

Same person. Same birth. Two calendars. Two birthdays.