🐉Roll a d20, with advantage if you have earned it.

✓ Tested & verified Updated: Aug 6, 2026 How the randomness works

D20 roller

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1d20 — every face equally likely

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How much does advantage actually help on a d20?

It raises your average roll from 10.5 to about 13.82 — roughly the same as a +3 bonus, but concentrated where it matters most. Advantage means rolling two twenty-sided dice and keeping the higher; disadvantage rolls two and keeps the lower, dragging the average down to about 7.18.

Advantage does not help evenly, which is why it feels stronger than a flat bonus. Against a target you would hit half the time it adds about 25 percentage points of success; against a target you almost always hit, or almost never do, it adds very little. A +3 modifier is worth the same 15% whatever you are rolling against. Advantage is a lever that presses hardest on the coin-flip rolls, which are exactly the ones the table cares about.

It also doubles your chance of a natural 20, from 5% to 9.75%, and cuts the chance of a natural 1 from 5% to 0.25%. Disadvantage flips both figures precisely the other way.

The same target number, rolled three ways. This is what advantage is worth in the only currency that matters at the table — the chance of actually succeeding.

Need to roll	Normal	Advantage	Disadvantage
5 or higher	80%	96%	64%
10 or higher	55%	79.8%	30.3%
11 or higher	50%	75%	25%
15 or higher	30%	51%	9%
20 exactly	5%	9.75%	0.25%
Average roll	10.5	13.82	7.18

The swing peaks in the middle, at 25 percentage points on an even-odds check, and shrinks at both ends. That is the whole shape of the mechanic: it rescues you from uncertainty, not from impossibility.

For every other die in the set — d4 through d100, up to ten at a time — use the dice roller. For deciding who rolls first, the random name picker settles it without an initiative order.

Frequently asked questions

What is the average roll on a d20?

10.5 — the mean of 1 through 20, which is why no single roll ever produces it. With advantage the expected value rises to about 13.82, and with disadvantage it falls to about 7.18. Those two numbers are the reason a game master handing out advantage casually is making a much larger concession than they usually think.

How do advantage and disadvantage work?

Roll two d20 and keep the higher for advantage, the lower for disadvantage. This roller does both for you and shows the discarded die as well as the kept one, which matters at the table — seeing the 19 you threw away is half the drama. If you have both advantage and disadvantage, the standard rules cancel them out and you roll a single die.

Does advantage stack if I have two sources?

Not under the standard rules — advantage is a binary state, so two sources give the same two-dice roll as one. Mechanically that is also the sensible cap: rolling three and keeping the highest would push the average to about 15.5, at which point the die stops being a source of tension and becomes a formality.

How often will I roll a natural 20?

One time in twenty, or 5%, on a normal roll — about once every four rounds of a typical combat with a few attacks each. Advantage nearly doubles that to 9.75%, since you miss a 20 only when both dice miss it. Under disadvantage it collapses to 0.25%, which is one session in a very long campaign.

Is a virtual d20 fairer than a plastic one?

Generally yes. A d20 has twenty faces and the most manufacturing error of any common die: bubbles in the resin, uneven trimming and rounded corners all shift the balance, and a cheap set can be measurably skewed. A crypto-random draw has no geometry to get wrong. What it lacks is the tactile ritual, which for many players is the point of dice.

Can I roll several d20 at once for a group check?

This page is built around the single-die-with-advantage case. For several independent d20s in one go, the dice roller takes any die type and up to ten of them, with the individual results and the total. Use this page when the two-dice keep-high or keep-low rule is what you actually want.

How the randomness works

A normal roll draws one value from crypto.getRandomValues and maps it to 1–20 with rejection sampling, so each face has exactly a 5% chance and none of the low numbers are favoured by a modulo shortcut. Advantage and disadvantage draw two fully independent values and keep the higher or lower, discarding nothing before the comparison — the expected values of 13.82 and 7.18 follow from the order statistics of two uniform draws over 1–20. The discarded die is shown alongside the kept one. No roll is stored or transmitted, and no result influences the next one.

Worked example

With Die d20, How many dice 1, this page works out You rolled —. 1d20 — every face equally likely

Sources:

What the average roll hides

Advantage is the cleanest bit of design in modern tabletop rules because it replaces arithmetic with a gesture. Nobody has to remember whether the bonus was +2 or +4; they just pick up a second die. The cost is that it is easy to hand out too freely, and its value is invisible until you look at the numbers.

Those numbers are worth carrying: advantage is worth about +3.3 on average, but it can be worth the equivalent of +5 on a roll you were going to make half the time, and almost nothing on a roll you were going to make anyway. So the moment to grant it is when the outcome is genuinely in doubt — and the moment it changes nothing is when a player has already stacked their bonuses so high that only a natural 1 can stop them.

The die also cannot tell you whether the roll should have been called for. That remains the one part of the game no generator handles.