Welcome to THAC0 . . . with Advantage! We’re two friends that have been playing D&D a long time. While we both love lots of other RPGs, D&D is our comfort food, and the internet is all about sharing pictures of your meals!

For anyone who hasn’t seen quite as many decades of D&D as we have, THAC0 stands for To Hit Armor Class Zero, which first appeared in the AD&D 1st edition DMG for monsters, and became standard for players in the 1985 Basic Boxed Set, as well as AD&D 2e. Instead of getting a bonus to hit, Armor Class descended, so negative numbers were better. That means you would add your target’s armor class from your d20 roll to see if you hit your THAC0.

This rule was likely created by math teachers to promote our ability to do Algebra.