Roll a d20
One tap, one die. Add your bonus, roll with advantage or disadvantage, and see whether you beat the DC.
Tip: press the space bar to roll.
d20
Tap the big die to roll.
What advantage is really worth
Advantage means rolling twice and keeping the better die. It feels like a flat bonus, but its value depends entirely on the number you need. Slide the target and compare.
Needing a 11, advantage is worth about +5.0 on the die. It peaks near +5 when you need an 11, and shrinks toward +1 at the extremes, which is why the 2014 rules' "passive" shortcut of ±5 is only exact in the middle.
Maths: with a success chance p on one die, advantage succeeds with 1 − (1 − p)², disadvantage with p².
d20 odds table
The chance of rolling at least a given number on the die, before modifiers.
| Need | Straight | Advantage | Disadvantage |
|---|---|---|---|
| 1+ | 100% | 100% | 100% |
| 2+ | 95% | 99.8% | 90.3% |
| 3+ | 90% | 99% | 81% |
| 4+ | 85% | 97.8% | 72.2% |
| 5+ | 80% | 96% | 64% |
| 6+ | 75% | 93.8% | 56.3% |
| 7+ | 70% | 91% | 49% |
| 8+ | 65% | 87.8% | 42.3% |
| 9+ | 60% | 84% | 36% |
| 10+ | 55% | 79.8% | 30.3% |
| 11+ | 50% | 75% | 25% |
| 12+ | 45% | 69.8% | 20.3% |
| 13+ | 40% | 64% | 16% |
| 14+ | 35% | 57.7% | 12.2% |
| 15+ | 30% | 51% | 9% |
| 16+ | 25% | 43.8% | 6.25% |
| 17+ | 20% | 36% | 4% |
| 18+ | 15% | 27.8% | 2.25% |
| 19+ | 10% | 19% | 1% |
| 20+ | 5% | 9.75% | 0.25% |
Typical DCs
The rules suggest DC 5 for very easy tasks, 10 easy, 15 medium, 20 hard, 25 very hard and 30 nearly impossible. A level-1 character with a +5 in a skill beats DC 15 exactly half the time.
Questions
What does rolling a d20 mean?
It means rolling a 20-sided die and reading the top face, a number from 1 to 20. In D&D almost every uncertain action (attacks, saving throws, ability checks) is a d20 roll plus a modifier, compared against a target number.
How much is advantage worth?
It depends on the number you need. If you need an 11 or higher (a 50% chance), advantage raises it to 75%, roughly the same as a +5 bonus. If you need a 2 or a 20, advantage adds much less. The explainer on this page shows the exact figures for every target.
What are the odds of a natural 20?
A straight d20 gives a natural 20 5% of the time (1 in 20). With advantage it is 9.75%, and with disadvantage 0.25% (1 in 400).
Does a natural 20 always succeed?
On an attack roll, yes: a natural 20 always hits and is a critical hit, and a natural 1 always misses. For ability checks and saving throws the core rules have no automatic success, though many tables play that way.
Can I add my modifier?
Yes. Set your bonus and the roller shows the die, the modifier and the total, and colours the result against the DC you set.