Calculator Inputs
Example Data Table
| Scenario | Attack Bonus | Target AC | Attacks | Damage Dice | Target HP | Use Case |
|---|---|---|---|---|---|---|
| Fighter versus ogre | +7 | 16 | 2 | 1d8 + 4 | 59 | Basic melee planning |
| Rogue with advantage | +8 | 15 | 1 | 1d8 + 4d6 + 5 | 45 | Sneak attack estimate |
| Spellcaster save spell | +0 | 14 | 1 | 1d4 | 70 | Save damage comparison |
Formula Used
Effective AC = Target AC + cover bonus.
Single hit chance = successful d20 attack results divided by 20. Natural 1 misses. Natural 20 hits.
Advantage chance = 1 - (1 - single chance)2.
Disadvantage chance = single chance2.
Normal hit chance = final hit chance - final critical chance.
Average die damage = number of dice × (die sides + 1) ÷ 2.
Critical damage doubles damage dice, then adds static bonuses.
Expected weapon DPR = attacks × [(normal hit chance × normal damage) + (critical chance × critical damage)].
Save fail chance = failed save rolls divided by 20, adjusted for advantage or disadvantage.
Expected spell damage uses full damage on failed saves. It adds half damage on successful saves when selected.
How To Use This Calculator
- Enter attacker and target names for cleaner exports.
- Add attack bonus, target AC, cover, attacks, and critical range.
- Enter weapon dice like 1d8, 2d6, or 1d8+2d6.
- Add damage bonuses, resistance, vulnerability, or immunity.
- Enter save DC, target save bonus, and spell damage details.
- Press calculate to show results above the form.
- Download the result as CSV or PDF for later notes.
Advanced DND 5E Combat Planning
A combat round can change quickly. One missed attack can save a monster. One strong critical hit can end a fight early. This calculator helps you read those chances before dice hit the table. It combines attack rolls, defense values, damage dice, critical ranges, saving throws, resistance, vulnerability, and enemy health.
Why Expected Damage Matters
Expected damage is not a promise. It is an average result across many similar turns. A rogue may roll poorly once. A fighter may land every strike. Over time, the average shows which option is stronger. It also helps a Dungeon Master judge whether a creature may survive one round or several rounds.
Better Encounter Balance
Challenge ratings give a broad guide. They do not know your table. They do not know magic items, tactics, terrain, buffs, or party focus fire. This tool gives another layer of planning. You can test an archer with advantage, a tank behind cover, or a spellcaster forcing a difficult save.
Attack And Save Support
The attack section estimates normal hits and critical hits. It respects natural one misses and natural twenty hits. It can also model advantage and disadvantage. The saving throw section estimates spell pressure. It lets you include half damage on success, which is common for many area spells.
Damage Adjustments
Resistance, vulnerability, and immunity often decide real combat value. A strong weapon can become weak against a resistant target. A modest spell can become deadly against a vulnerable enemy. The calculator applies these adjustments after the average damage is estimated.
Using Results At The Table
Use the result as a planning guide, not as a script. Dice still create drama. Smart monsters may retreat. Heroes may spend resources. Conditions may change the next round. Review hit chance, expected damage, and rounds to defeat together. Then choose the tactic that fits the story, the battlefield, and the fun of the group.
Exporting And Review
Download the CSV when you want raw numbers for notes. Use the PDF when you need a cleaner handout. Both exports help compare builds, monsters, and tactics later. They also make repeated testing easier for campaigns, boss fights, arenas, and one shot encounters during careful session prep too.
FAQs
What does this combat calculator estimate?
It estimates hit chance, critical chance, average damage, expected damage per round, save failure chance, spell damage, and rounds needed to defeat a target.
Does it support advantage and disadvantage?
Yes. It supports advantage and disadvantage for attack rolls and saving throws. The calculator applies probability formulas for two d20 rolls.
How should I enter damage dice?
Enter dice in common notation, such as 1d8, 2d6, 4d6, or 1d8+2d6. Add flat damage in the bonus field.
Does critical damage double all damage?
The calculator doubles dice damage for critical hits. It then adds static bonuses once, matching the usual combat damage method.
Can this replace encounter judgment?
No. It is a planning aid. Terrain, tactics, resources, conditions, and player choices can change combat results during play.
How does resistance work here?
Resistance halves the average damage after the normal or critical damage is calculated. Vulnerability doubles it. Immunity makes it zero.
Does the save section include half damage?
Yes. Choose yes for half damage on a successful save. Choose no for spells that deal damage only on a failed save.
Why are results shown as averages?
Averages help compare options fairly. Actual dice rolls can be much higher or lower during a single round.