“The Lotus guys probably figured it didn’t matter to be wrong”: Excel thinks 1900 was a leap year because of a small shortcut taken in the ’80s — I’ll think of this next time I want to cut corners

Microsoft Excel was originally created as competition for Lotus 1-2-3, which has had lasting effects on my favorite spreadsheet software. Here’s how a small shortcut taken in the ’80s has lasted through until 2026.