d20 odds
- •Average roll: 10.5 (add the lowest and highest face and halve it: (1 + 20) / 2)
- •Each face: 1 in 20, or 5%
- •Chance of rolling 20: 5% per roll, 9.75% to see at least one in two rolls
| Need | Normal | Advantage | Disadvantage |
|---|---|---|---|
| 2 or higher | 95% | 99.75% | 90.25% |
| 5 or higher | 80% | 96% | 64% |
| 8 or higher | 65% | 87.75% | 42.25% |
| 10 or higher | 55% | 79.75% | 30.25% |
| 11 or higher | 50% | 75% | 25% |
| 12 or higher | 45% | 69.75% | 20.25% |
| 15 or higher | 30% | 51% | 9% |
| 18 or higher | 15% | 27.75% | 2.25% |
| 20 or higher | 5% | 9.75% | 0.25% |
Advantage, disadvantage and natural 20s
Advantage rolls two d20s and keeps the higher. It raises the average from 10.5 to 13.825, and lifts the chance of a natural 20 from 5% to 9.75%. Disadvantage keeps the lower die: the average drops to 7.175 and a natural 1 comes up 9.75% of the time.
Advantage helps most when you need a roll in the middle of the die. Needing 11 or higher goes from 50% to 75%. At the edges it adds little: needing a 20 only goes from 5% to 9.75%. Several sources of advantage do not stack, and having both advantage and disadvantage cancels out to a single d20.
Type your DC or the target's AC into the Chance to hit box above to see these odds for your own bonus.
What uses a d20 in D&D 5e
- •The three core rolls: attack rolls, ability checks and saving throws are all d20 + modifiers against an AC or DC.
- •Natural 20 and 1: on an attack roll a 20 always hits (a critical hit) and a 1 always misses, whatever your total. Ability checks and saving throws have no automatic success or failure in the core rules.
- •Death saving throws: 10 or higher is a success. A natural 20 brings you back with 1 hit point; a natural 1 counts as two failures. That makes a death save 55% to succeed.
- •Initiative: a Dexterity check, so d20 + your Dexterity modifier. Track the order with the initiative tracker.