5E Combat Calculator

Estimate hit chance, critical chance, average damage, total expected DPR, and rough rounds to defeat a target in Dungeons and Dragons 5e. This calculator uses exact d20 probability logic for normal rolls, advantage, and disadvantage, then visualizes expected damage across a range of Armor Class values.

Combat Inputs

Results

Expert Guide to Using a 5e Combat Calculator

A 5e combat calculator is one of the most useful planning tools for players, dungeon masters, and encounter designers because it turns uncertain combat outcomes into measurable probabilities. In Dungeons and Dragons 5th Edition, every attack involves several interconnected variables: attack bonus, target Armor Class, number of attacks, advantage or disadvantage, critical hit rate, and average damage per successful strike. Even experienced players often estimate these values by feel rather than by math, but small changes in accuracy or damage can produce surprisingly large differences in expected combat output over several rounds.

This calculator focuses on the core question most martial and hybrid builds ask during optimization: “How much damage should I expect to deal against a target with a given AC?” Rather than guessing, the calculator computes exact roll outcomes on a d20 under standard 5e assumptions. That means natural 1s still miss, natural 20s still hit, and critical damage doubles only the damage dice. If you enable advantage or disadvantage, the calculator evaluates the change in your hit and crit rates directly, which is especially helpful when comparing tactics such as fighting from stealth, using Reckless Attack, restraining a target, or attacking while poisoned or blinded.

What the calculator measures

The most important output is expected damage per round, often shortened to DPR. This value is not a guarantee. Instead, it is the long-run average amount of damage a combatant would deal if the same attack sequence happened many times. Expected DPR is useful because it allows apples-to-apples comparison between very different combat options, such as a high-accuracy build with lower damage versus a swingier build with heavier weapon dice.

• Hit chance: The probability that an attack connects and is not a critical hit.
• Critical chance: The probability that the attack lands as a critical hit.
• Average damage on hit: The mean damage of a normal successful attack.
• Average damage on crit: The mean damage when damage dice are doubled.
• Expected damage per attack: Probability-weighted average damage for one attack roll.
• Total DPR: Expected damage per attack multiplied by the number of attacks.
• Estimated rounds to defeat: Target HP divided by expected DPR.

Why Armor Class and attack bonus matter so much

In 5e, attack accuracy scales in a relatively bounded way compared with some earlier editions. Since attack bonuses and Armor Class values stay within a tighter range, every +1 matters. If you need a 10 or higher on a d20 to hit, your chance is meaningfully different than if you need a 9 or higher. Because each point changes the number of successful die faces, your expected DPR can move substantially even when your weapon or class abilities remain unchanged.

Suppose an attacker has a +7 attack bonus. Against AC 16, the attacker hits on a roll of 9 through 19 and crits on 20. That gives a 55% non-crit hit rate and a 5% crit rate on a normal roll, for 60% total hits. If that same attacker fights AC 18 instead, the non-crit hit chance drops to 45% while crit remains 5%. The total falls to 50%. That 10-point percentage drop often matters more than adding a small amount of flat damage.

Attack Bonus	Target AC	Roll Needed	Normal Hit Rate	Crit Rate	Total Hit Rate
+5	15	10+	50%	5%	55%
+7	16	9+	55%	5%	60%
+9	18	9+	55%	5%	60%
+11	20	9+	55%	5%	60%

The table above illustrates bounded accuracy in action. Notice that several different attack bonus and AC combinations produce the same needed die roll and therefore the same probability. This is one reason a 5e combat calculator is so valuable: it strips away the noise and shows the exact expected outcome for the current matchup.

Advantage and disadvantage change more than many players expect

One of the strongest tactical effects in 5e is advantage. Rolling two d20s and taking the higher result significantly boosts hit probability, but the exact impact depends on the number you need. Advantage is especially strong when you need a middling result, and it also raises your critical hit rate because any qualifying die can trigger the crit. Conversely, disadvantage lowers hit rate and sharply suppresses criticals.

Needed on d20	Normal Hit Chance	Advantage Hit Chance	Disadvantage Hit Chance
8+	65%	87.75%	42.25%
10+	55%	79.75%	30.25%
12+	45%	69.75%	20.25%
15+	30%	51.00%	9.00%

These are real probability values derived from d20 outcomes. For example, if you normally need a 10 or better, your chance is 55% on one die. With advantage, the chance to fail both dice is 45% times 45%, or 20.25%, so the success chance becomes 79.75%. This is why features that reliably generate advantage can outperform raw damage boosts in many practical combat situations.

How average damage is computed

Damage dice have simple average values. A d4 averages 2.5, a d6 averages 3.5, a d8 averages 4.5, a d10 averages 5.5, and a d12 averages 6.5. If your attack deals 1d8 + 4, the average damage on a normal hit is 8.5. On a critical hit, standard 5e rules double only the dice, so the crit average becomes 2d8 + 4, or 13.0. The calculator multiplies each average by its exact probability and then sums the results. That gives a mathematically correct expected value for one attack. It then multiplies by your number of attacks for the round total.

1. Determine hit probability based on attack bonus and target AC.
2. Separate critical hits from ordinary hits.
3. Calculate normal hit average using standard die means.
4. Calculate crit average by doubling the dice only.
5. Multiply each outcome by its probability.
6. Add the values to get expected damage per attack.
7. Multiply by attacks to estimate round output.

When expected DPR can mislead you

Expected DPR is powerful, but it is not the whole story. Real 5e combat includes resource constraints, concentration, positioning, resistances, immunities, temporary hit points, damage riders, conditional effects, and action economy disruption. A build that has slightly lower expected DPR may still be tactically superior if it imposes prone, stun, grapple, fear, or battlefield control. Likewise, nova damage that depends on limited spell slots or short-rest abilities should be evaluated separately from sustained DPR.

You should also remember that expected rounds to defeat a target is a smooth average, not a simulation of real turn-by-turn variance. If the calculator says 3.4 rounds, actual play may still end in 2 rounds after high rolls or take 5 rounds after misses. The estimate is best used for planning and comparison, not for exact prediction at the table.

If your character has extra dice that apply only once per turn, such as Sneak Attack, or only under a condition, such as Divine Smite after a hit, this simple calculator should be treated as a baseline model rather than a complete build simulator.

Practical uses for players and dungeon masters

Players can use a 5e combat calculator to compare feats, fighting styles, weapon swaps, and tactical choices. For example, a player deciding between a shield and a two-handed weapon can test whether the damage gain offsets the loss in survivability. A ranged attacker can compare fighting under disadvantage in melee versus moving and provoking an opportunity attack. A fighter can estimate the value of Action Surge turns by calculating a larger number of attacks. A champion can model expanded critical ranges to see how much crit frequency actually contributes against different ACs.

Dungeon masters benefit too. Encounter pacing often depends on how quickly monsters and player characters can reduce each other’s hit points. If a party’s front-line attacker consistently outputs high DPR against moderate AC monsters, a DM might choose creatures with stronger defensive traits, more hit points, cover access, or disruptive mobility rather than simply inflating numbers blindly. By contrast, if the party struggles to hit armored foes, adding objectives, terrain, or weaker minions may produce a better experience than repeatedly deploying high-AC bruisers.

Interpreting the chart below the calculator

The chart plots expected damage against a range of Armor Class values so you can see how resilient your attack profile is as defenses rise. A flatter curve indicates a build that remains reliable over a broad range of AC values, while a steep decline usually signals a setup that depends heavily on favorable accuracy assumptions. This is useful when evaluating bless, magical weapons, advantage generation, Archery fighting style, or other accuracy modifiers.

Best practices for meaningful comparisons

• Compare one change at a time, such as +1 to hit versus +2 damage.
• Use realistic enemy AC and HP values from your campaign tier.
• Model normal, advantage, and disadvantage separately.
• Account for your real number of attacks, not idealized nova turns only.
• Use sustained assumptions when judging overall build value.

Probability literacy improves tactical play

Many tabletop decisions become clearer when viewed through probability instead of intuition. If two options feel close, exact hit and crit rates can reveal the better line. This is not about reducing the game to spreadsheets. It is about understanding how the rules interact so that your choices become intentional. Knowing that advantage may be worth more than a small damage rider, or that a +1 bonus can noticeably improve multiattack output, helps you spend actions, spells, and class features more effectively.

For readers interested in the math foundations behind probability, randomness, and statistical expectation, these authoritative references are useful background materials: NIST Engineering Statistics Handbook, Penn State Probability Theory, and UC Berkeley Statistics Resources.

Final takeaway

A 5e combat calculator is not just an optimizer’s toy. It is a practical decision aid for anyone who wants a better sense of how attacks perform in live play. By combining attack bonus, target AC, average damage, number of attacks, and roll state, you get a realistic estimate of both consistency and output. Use it to compare builds, tune encounters, and understand when accuracy, critical rate, or extra attacks give the strongest payoff. The best combat decisions in 5e usually come from balancing math, positioning, and party coordination, and this calculator helps with the math side quickly and clearly.