DND 5E Damage Calculator

Calculator Form

Calculation mode

Roll state

Damage instances

Attack bonus

Target armor class

Critical range starts at

Save DC

Target save bonus

Damage on successful save

Main dice count

Main dice sides

Flat damage bonus

Extra dice count

Extra dice sides

Critical dice multiplier

Damage adjustment

Example Data Table

Scenario	Mode	Inputs	Expected Use
Longsword strike	Attack	+5 vs AC 15, 1d8 + 3, one attack	Compare weapon accuracy and average damage.
Greatsword attack	Attack	+6 vs AC 16, 2d6 + 4, one attack	Check heavy weapon expected damage.
Sneak attack hit	Attack	+7 vs AC 15, 1d6 + 4, extra 3d6	Estimate bonus dice impact.
Fire spell save	Save	DC 15, target +3 save, 8d6, half on success	Review spell damage against saves.

Formula Used

Average dice damage: Dice count × ((Dice sides + 1) ÷ 2).

Attack expected damage: ((Normal hit chance × Normal damage) + (Critical chance × Critical damage)) × Damage instances × Damage adjustment.

Saving throw expected damage: ((Failure chance × Full damage) + (Success chance × Full damage × Success ratio)) × Damage instances × Damage adjustment.

Critical damage: Average damage dice × Critical dice multiplier + Flat damage bonus.

Damage adjustment: normal = 1, resistance = 0.5, vulnerability = 2, immunity = 0.

How to Use This Calculator

Select attack roll mode or saving throw mode.
Enter the d20 roll state, such as normal, advantage, or disadvantage.
Add attack bonus and armor class for attack calculations.
Add save DC, save bonus, and success damage ratio for save calculations.
Enter main dice, extra dice, flat bonus, and critical settings.
Choose resistance, vulnerability, immunity, or normal damage.
Press the calculate button to view results above the form.
Use CSV or PDF buttons to save the result.

Understanding the Damage Calculator

Damage planning in a tabletop fight is partly arithmetic and partly uncertainty. This calculator treats each attack, save, and damage roll as a probability problem. It does not replace rulings at the table. It gives a clear estimate before choices are made.

A player can test weapon damage, spell damage, monster attacks, or repeated strikes. The tool separates hit chance, critical chance, miss chance, average damage, and adjusted damage. That makes it useful for comparing feats, magic weapons, buffs, resistance, vulnerability, and different target defenses.

Why Probability Matters

A single roll can feel dramatic, but long term damage follows expected value. Expected value multiplies each possible outcome by its chance. A normal hit uses average dice plus flat bonuses. A critical hit multiplies damage dice, then adds the same flat bonuses. Resistance, vulnerability, or immunity is applied after the hit or saving throw result.

Advantage and disadvantage change the final d20 distribution. Advantage makes high rolls much more common. Disadvantage makes low rolls more common. Because of that, the same attack bonus can produce very different expected damage. This is important when checking cover, conditions, inspiration, or class features.

Useful Combat Comparisons

Use the calculator to compare two weapons against the same armor class. Then compare the same weapon against several armor classes. You can also change the critical range to study features that improve critical hits. Add extra dice for smite, sneak attack, hunter’s mark, or similar effects.

For saving throw damage, choose a save bonus, difficulty class, and success result. Half damage on a successful save is common, but some effects deal no damage. The calculator can estimate both cases. Damage multipliers then show how resistance or vulnerability changes the final expectation.

Practical Limitations

The result is an estimate, not a promise. It assumes independent attacks and average dice behavior. It does not judge positioning, action economy, target priorities, concentration checks, terrain, or encounter story goals. Those factors still matter.

Use these numbers as a planning aid. A balanced encounter still needs pacing, objectives, and player agency. Statistics can guide design, but the best combat scenes also leave room for surprise, risk, and memorable decisions during every important battle round at the table tonight.

FAQs

What does expected damage mean?

Expected damage is the average damage over many similar attempts. It combines hit chance, critical chance, save outcomes, dice averages, and damage modifiers.

Does the calculator roll random dice?

No. It uses average dice values and probability. This makes results stable, repeatable, and useful for comparing different combat options.

How is advantage calculated?

Advantage uses the better result from two d20 rolls. The calculator changes the d20 probability distribution before checking hit or save outcomes.

How is disadvantage calculated?

Disadvantage uses the lower result from two d20 rolls. This increases low results and usually reduces expected damage for attack rolls.

Are flat bonuses doubled on critical hits?

No. This calculator doubles only damage dice by default. Flat bonuses are added after the critical dice multiplier is applied.

Can I calculate sneak attack or smite damage?

Yes. Add those dice under extra dice. They are included in normal damage and multiplied by the critical dice multiplier.

How does resistance affect results?

Resistance multiplies final expected damage by 0.5. Vulnerability doubles it. Immunity reduces the adjusted expected result to zero.

Can this help balance encounters?

Yes. It helps compare likely damage output. Still consider tactics, terrain, objectives, healing, resources, and player decisions before final balancing.