A natural 20 is a Dungeons & Dragons rule term for rolling a result of 20 on a 20-sided die, the maximum possible value, before any bonuses are applied.
It is distinguished from a modified 20, which is a total result of 20 acquired by adding a bonus to a die roll lower than 20.
Game rules in various editions of Dungeons & Dragons grant a special effect when the player rolls a natural 20.
In several editions of the D&D rules, a natural 20 is an automatic hit on an attack roll, regardless of the opponent's armor class. This occurs in AD&D 1st edition, 2nd edition, D&D 3rd edition, 4th edition, and 5th edition.
In D&D 3rd edition, a natural 20 is an automatic success on a saving throw.
Contrary to popular belief, a natural 20 is not an automatic success on skill checks or ability checks in D&D 3rd, 4th, or 5th edition. It is not an automatic success on saving throws in D&D 5th edition.
In D&D 3rd and 4th edition, a natural 20 on an attack roll may trigger a critical hit.
In 3rd edition, a second attack roll must be made to confirm the critical; if this is successful, the attack deals double damage. Various weapons and character options allow criticals to be threatened on more numbers, or to deal more than double damage. In 4th edition, any natural 20 which would also be a hit is automatically a critical hit, and deals maximum possible damage for the dice.
In D&D 5th edition, critical hits are confirmed automatically.
Due to roll-under mechanics used in some editions of D&D prior to D&D 3rd edition (2000), a natural 20 can be the worst roll, and an automatic failure. This is the case with non-weapon proficiencies in AD&D 2nd edition.
Many gaming groups use other rules which trigger on a natural 20. Common rules include giving an exceptionally good result or automatic success where those do not apply.
The term "natural 20" appeared in the article From the Sorcerer's Scroll, Dragon #16 (Jul 1978), p.16, by Gary Gygax. Gygax was critical of popular house rules allowing a critical hit:
- "The "critical hit" or "double damage" on a "to hit" die roll of 20 is particularly offensive to the precepts of D&D as well. Two reciprocal rules which go with such a system are seldom, if ever mentioned: 1) opponents scoring a natural 20 will likewise cause a double damage hit or critical hit upon player characters; and 2) as a 20 indicated a perfect hit, a 1 must indicate a perfect miss, so at any time a 1 is rolled on the "to hit" die, the attacker must roll to find if he or she has broken his or her weapon, dropped it, or missed so badly as to strike an ally nearby."
The concept of a natural 20 has been popularized by players of Dungeons & Dragons 3rd edition and onward, where it has entered gaming parlance to refer to any great or unexpected critical success.