Find out the exact odds of any roll before your players pick up the dice. This free dice probability calculator shows the chance of every result, the average, and the odds of hitting a target number, plus hit chance and average damage for attacks against AC and saving throw spells in D&D 5E and Daring & Dread.
Three ways to calculate
Any roll
Type any dice expression to see the chance of every result, the average, the range, and the chance of rolling at least a target number. Click an example to try it.
Attack vs. AC
Enter an attack bonus, the target’s AC, and the damage. You get the hit chance, the critical hit chance, the average damage per turn, and the chance of dropping a target with a set number of hit points. It handles advantage, disadvantage, Elven Accuracy, Lucky, wider critical ranges, multiple attacks, Sneak Attack and other once-per-turn damage, and Great Weapon Fighting.
Saving throw
Enter a spell’s save DC, the target’s save bonus, and the damage. You get the chance the target fails, its average damage, and how the damage spreads out, with half damage, no damage, or full damage on a success.
Compare your options
Press Pin to compare to keep a result on the chart, then change something and see both side by side. It’s the quickest way to settle questions like whether a greatsword beats a greataxe, whether a feat is worth it, or how much advantage really helps.
Dice notation
- 2d6+3: two six-sided dice plus three
- 4d6kh3 or 4d6dl1: roll four and keep the highest three
- d20adv+5 and d20dis+5: advantage and disadvantage
- 3d20kh1: the best of three, like Elven Accuracy
- 2d6r2: reroll 1s and 2s once
- d8min2: treat any roll below 2 as 2
- 3d6!: exploding dice, where a maximum roll adds another die
- (1d8+3)*2 and 8d6/2: multiply, or divide and round down
Put this tool on your own site
Run a blog, a campaign wiki, or a club website? You’re welcome to add the Dice Probability Calculator to it for free. Copy the code below and paste it into an HTML or custom code block. It works with WordPress, Blogger, Squarespace, Wix, and most other site builders.
Frequently asked questions
How do I find the chance to hit in 5E?
Subtract your attack bonus from the target’s AC and you get the number you need on the d20. Each number on the die is a 5% chance. A natural 1 always misses and a natural 20 always hits. The Attack vs. AC tab does this for you, including advantage, critical hits, and bonus dice like Bless.
What is the average damage of an attack?
Average damage is your chance to hit times your average damage on a hit, plus a bit more for critical hits. The calculator works it out exactly, including misses, crits, multiple attacks, and once-per-turn damage like Sneak Attack.
How much does advantage help?
Advantage is worth about +3 to +5 on a d20 roll when you need a middle result. It helps most when you need around an 11, and less when you need a very high or very low number. Compare them by pinning one result and switching to the other.
What dice notation can I use?
Standard notation like 2d6+3, plus kh and kl to keep the highest or lowest dice (4d6kh3), dl and dh to drop dice, r to reroll low results once (d6r2), min to raise low rolls (d8min2), ! for exploding dice, and adv or dis for advantage and disadvantage (d20adv+5).
Are these results exact?
Yes. The calculator works out every possible result mathematically instead of rolling thousands of random tests, so the percentages are exact.
How do saving throw spells work?
The target rolls a d20 and adds its save bonus. If the total equals or beats your spell save DC, it succeeds and usually takes half damage. The Saving throw tab shows the chance a target fails and its average damage.
More free GM tools
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- Dice Roller: every polyhedral die, with advantage, disadvantage, and bonuses
- Encounter Difficulty Calculator: how deadly a fight is under 5E or Daring & Dread rules
- Point Buy Calculator: ability scores with the 27-point buy and species or background bonuses
- Treasure Hoard Generator: coins, gems, art objects, and magic items by challenge rating
About the creator
These free tools are made by Darrin Drader, designer of Daring & Dread: The Roleplaying Game, a ground-up rebuild of 5E for tables that want their victories to mean something. For adventures, maps, and more GM resources, see Adventures, Maps & Tools.