5e combat calculator

What this 5e combat calculator does

This tool estimates your average performance in combat using core Dungeons & Dragons 5e attack rules. It calculates your chance to hit, chance to crit, expected damage per attack, total expected damage per round (DPR), and how many rounds you might need to defeat a creature with a given hit point total.

It is designed for fast table decisions: comparing weapon options, choosing between feats, evaluating a buff spell, or checking if your current turn plan is likely to finish an enemy.

How the math works

1) Hit chance and critical chance

The calculator evaluates all d20 outcomes directly. A natural 1 always misses. A roll in your critical range (normally 20, or 19–20 for some builds) is treated as a critical hit. Otherwise, a roll hits if:

d20 + attack bonus ≥ target AC

For advantage and disadvantage, it checks all 400 two-d20 combinations and applies max/min accordingly. This gives exact probabilities, not approximations.

2) Average damage on a hit

Expected value for dice is computed as:

average dice damage = number of dice × (die size + 1) / 2

Normal hit damage = average dice damage + flat bonus.
Critical hit damage = doubled damage dice + flat bonus (standard 5e rule for weapon attacks and most damage dice).

3) Expected DPR

The final expected damage per attack is:

(non-crit hit chance × normal hit damage) + (crit chance × crit damage)

Multiply that by attacks per round for DPR. Divide target HP by DPR for an average rounds-to-defeat estimate.

Practical ways to improve your DPR

• Increase attack bonus when fighting high-AC enemies; accuracy often beats small damage boosts.
• Gain advantage through positioning, conditions, class features, or team setup.
• Add more attacks (Extra Attack, bonus-action attacks, reactions when available).
• Boost damage dice for builds with high crit frequency.
• Watch AC breakpoints; even +1 to hit can be a major DPR jump at key thresholds.

Limitations and assumptions

This calculator is intentionally streamlined. It does not automatically include resistances, vulnerabilities, smites/spell slots, rerolls (Great Weapon Fighting), on-hit riders, or effects that only trigger once per turn. It is best used as a baseline model for at-will attacks.

If you want a deeper simulation, you can still use this output as your starting point and then manually adjust for your campaign-specific conditions.