The Natural 20 Problem

Sep 05, 2026

“The Natural 20 Problem” is “Should rolling a Natural 20 always succeed?”

DM: “The Thief runs into the alley and disappears around the corner”
Player: “I lift the building to cut the distance”
DM: “Roll a d20”
Player: “20!”
DM: “You lift the building and see the Thief surrender in amazement!”

D&D 3.5

You always hit on a Natural 20, and you always Save on a Natural 20. Skill checks are not affected.

Skill Checks: a natural roll of 20 on the d20 is not an automatic success

Automatic Misses and Hits: A natural 20 is always a hit.

Automatic [Saving Throw] Failures and Successes: A natural 20 is always a success.

AD&D 1e

AD&D isn’t a d20 system, so the mechanics are a little different to talk about.

Skill checks in AD&D don’t really map to d20 skill checks. They have their own table, and we won’t discuss further.

Saving throws involve rolling a d20 and beating a number that’s dependent on your class and level, and nothing else. 20 always succeeds, but there’s nothing special about it per se.

Combat is a little more interesting, and I’ve excerpted the appropriate parts at the bottom of this article. 20 does not always hit, but if you roll it, it will hit a much better armour type than progression would imply. It does this by repeating the number 20 six times before continuing counting upwards.

So, for example, a Cleric rolling an 18 will hit AC 2; rolling a 19, AC 1; but rolling a 20 will hit AC 0 through -5. Then 21 hits a -6 and so forth. (If you’re not familiar with AD&D, the smaller the number, the better the armour - the opposite of d20 systems).

This section and post were inspired by a DM Angelo video on YouTube.

Classic d20

My thinking for Classic d20 is quite simple: for attacks and skill checks, add +5 to your roll on a Natural 20. This is less generous than 3.5, but mimics nicely AD&D’s progression of 20s. Jaime Lannister shouldn’t be vulnerable to every peasant who throws a rock at him, but a Hedge Knight should at least have a chance.

Example: You’re attacking a creature with AC 25. You have a +2 sword and a +1 STR bonus. You roll a Natural 20. Normally, this would be a total 23 - a miss. But you now get a +5, letting you hit anything up to AC 28.

I do like 3.5’s “automatic success” for Saving Throws: it makes sense, and Classic d20 will retain it.

I don’t like Critical Hits, as they’re more likely to hurt a PC than a Monster. Classic d20 does not have them.