D20 Roller: Roll a d20 with Advantage or Disadvantage
Roll a twenty-sided die online with a modifier, advantage or disadvantage for tabletop games such as Dungeons & Dragons. Shows both dice, the one kept and a history of your last 20 rolls.
Press Roll to roll 1d20.
About the D20 Roller
The D20 Roller rolls a twenty-sided die, the die behind almost every check, attack and saving throw in Dungeons & Dragons and many other tabletop role-playing games. The page opens on 1d20. Add your bonus with the Modifier picker or by typing it, for example 1d20+5, choose Normal, Advantage or Disadvantage, and press Roll. The page shows the die, the total with the modifier, and a history of your last 20 rolls.
With Advantage the roller rolls two d20s and keeps the higher one; with Disadvantage it keeps the lower one. The die that is set aside stays on screen, struck through, so the whole table can see both results. The modifier is added once, to the kept die.
How to use it
Steps
- Leave the notation on
1d20or add a modifier such as+3or-1. - Choose Advantage or Disadvantage if the rules call for it.
- Press Roll. Press it again for the next check; each roll goes to the top of the history.
Advantage applies to a single d20. If you change the notation to more dice, the option is switched off and the page says why. For other dice, such as damage rolls, use the full Dice Roller.
The odds
A fair d20 gives each face from 1 to 20 a chance of exactly 1 in 20, so the average roll is 10.5. With advantage, a result of at least fails only if both dice fail, so
and with disadvantage both dice must succeed, . A natural 20 has a 5% chance on one die, 9.75% with advantage and 0.25% with disadvantage. On average, advantage raises the kept die to about 13.8 and disadvantage lowers it to about 7.2, which is worth roughly a +3 or -3 modifier near the middle of the range.
How random is it?
The die is drawn from your browser's cryptographic random generator, crypto.getRandomValues, using rejection sampling so that no face is more likely than another. Nothing is remembered between rolls, so a run of low numbers says nothing at all about the next roll, however long the streak has been. For a quick random choice of another kind, try the Coin Flipper.
Privacy
Nothing is uploaded; every calculation runs in your browser and never leaves your device. Your rolls and history stay on this page and are gone when you close or reload it.
Frequently asked questions
What is rolling with advantage?
You roll two d20s and keep the higher result. Disadvantage is the opposite: you keep the lower one. Any modifier is added to the die you keep.
How much does advantage help?
On average the kept die rises from 10.5 to about 13.8, and the chance of a natural 20 nearly doubles, from 5% to 9.75%.
What is the chance of rolling a natural 20?
One in 20, or 5%, on a single d20. With advantage it is 1 − (19/20)², or 9.75%; with disadvantage it is 0.25%.
Why is the advantage option greyed out?
Advantage and disadvantage apply to a single d20. Set the notation to 1d20, with or without a modifier, and the options become available.
Is this d20 fair?
Yes. Every face from 1 to 20 is equally likely: the roll uses your browser's cryptographic random generator with rejection sampling, so no face is favoured.