The Armor Class (AC) in Dungeons and Dragons 5e is usually determined by what armor you wear, a feature you may have, or a spell you may be under the effects of. But what if you find yourself without any of those things? Then you have to rely on your base AC, the formula for which is:
Base AC = 10 + Dexterity Modifier
It’s important to note that the base AC only applies when a character is not wearing any armor or shields. If a character is wearing armor or a shield, their AC is calculated using the rules for that particular type of armor or shield.
Additionally, some creatures may have a base AC that is different from 10 plus their Dexterity modifier. For example, creatures with natural armor may have a base AC of 12 or 13, which includes their natural armor bonus and is not affected by Dexterity.
It’s also worth noting that certain spells, features, and magical items may modify a character’s base AC. For example, the Shield spell can be cast as a reaction to add 5 to your AC until the start of your next turn, while the Defensive Duelist feat allows you to use your reaction to add your proficiency bonus to your AC against a melee attack.
Overall, while the formula for base AC is relatively simple, it’s important to keep in mind the various factors that can affect a character’s AC in DnD 5E.
How is dexterity part of the base? If you are immobile your AC should only be 10. Also shouldn’t a natural armor bonus count as part of the base, since (unlike dex) you can never lose your natural armor bonus. By all logic base armor should be your AC without any bonus that can be removed, you know, the “base”.