Strange reason the calendar suddenly skipped forwards in October 1582 and 10 days vanished

A tweet has gone viral this week that shows 10 days missing from the calendar in October 1582, and everyone’s wondering what’s going on. Was there a glitch in the matrix? Did time suddenly just jump 10 days forward? No. But there is an interesting story behind it. Here’s a quick history lesson!

Someone literally scrolled all the way back to October 1582 on their iPhone calendar and found that it jumps straight from Thursday 4th October to Friday 15th October, but why? Well, these 10 days vanished when Pope Gregory XIII switched to the Gregorian Calendar in 1582.

Before that, they used the Julian calendar, but it wasn’t very accurate. The calendar was 365.25 days long, which was longer than the time it takes the Earth to revolve around the Sun. So, the Gregorian calendar shortened this by 0.0075 days to 365.2422, which seems like a ridiculously minuscule change.

What the fuck happened in October 1582 pic.twitter.com/lzFsCXWog2

— . (@emmasarchivee) May 20, 2026

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But it means the calendar is now accurate to the Sun, which stops the calendar from drifting about one day every 314 years. There was also an issue with the Julian calendar, where it had drifted so much that the March equinox was occurring well before its normal 21st March, which made it impossible to calculate the date of Easter.

When the Pope switched over to the new calendar, he advanced the date by 10 days, so Thursday, 4th October 1582 was followed by Friday, 15th October 1582, to bring everything in line.

The months and the lengths of the months are exactly the same in the Gregorian calendar as in the Julian calendar. The only difference is that the Julian calendar had a leap day every four years without exception, whereas the new calendar doesn’t have leap years in century years, like 1800, 1900 and 2000.

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Featured image credit: Instagram