Rollune
In 5e, a natural 20 on an attack roll hits automatically and is a critical hit: roll all the attack's damage dice twice, then add modifiers once. A natural 1 on an attack always misses. By the rules, natural 20s and 1s don't auto-succeed or auto-fail ability checks or saving throws, except death saves.
The rule in one line
Natural 20 on an attack roll = automatic hit + critical hit. Natural 1 on an attack roll = automatic miss. "Natural" means the number on the die itself, before modifiers.
Crit damage: double the dice, not the modifier
On a critical hit, roll every damage die of the attack twice, then add your modifiers once.
| Attack | Normal | Critical | Average crit |
|---|---|---|---|
| Longsword, +3 | 1d8+3 |
2d8+3 |
12 |
| Greataxe, +4 | 1d12+4 |
2d12+4 |
17 |
| Rapier + Sneak Attack (3d6), +4 | 1d8+3d6+4 |
2d8+6d6+4 |
34 |
| Fire Bolt (level 5) | 2d10 |
4d10 |
22 |
Spells that use attack rolls (like Fire Bolt) crit too; spells with saving throws (like Fireball) don't.
How often do crits happen?
- Normal: 5% (1 in 20)
- With advantage: 9.75%
- Crit on 19–20 (e.g. Champion fighter's Improved Critical): 10%, or 19% with advantage
- Crit on 18–20: 15%, or 27.75% with advantage
Details in advantage and disadvantage odds.
Checks and saves
By the core rules, a natural 20 on an ability check or saving throw is just a 20 plus your modifier; it can still fail a very high DC. The exception is death saving throws: a natural 20 brings you back with 1 hit point, and a natural 1 counts as two failures.
Popular house rules
- Max + roll: on a crit, one set of dice is maximized and the other is rolled (a 2d8 crit becomes 8 + 1d8). Feels great, reduces "I crit for 4" moments.
- Crit on checks: a natural 20 gives a bonus effect or an extra success, not an impossible result.
- Fumbles: a natural 1 causes a complication. Keep them mild and narrative (drop an arrow, lose footing); punishing fumbles hit characters with many attacks harder, since they roll more 1s.
Agree on house rules at session zero.
Roll your crits
The online dice roller highlights natural 20s and 1s on a single d20. In the Rollune app, save your normal and crit damage as presets so a crit is one tap.
