D&D 5e Calculator
Quickly compute your ability modifier, proficiency bonus, attack math, spell save DC, and expected damage per attack.
- Ability Modifier: +0
- Proficiency Bonus: +2
- Attack Bonus: +0
- Skill/Check Bonus: +0
- Spell Save DC: 10
- Passive Score: 10
- Hit Chance vs AC: 0%
- Crit Chance: 0%
- Expected Damage / Attack: 0.00
Note: This calculator assumes a natural 1 always misses and a natural 20 always hits and crits.
What This D&D 5e Calculator Helps You Do
If you play Dungeons & Dragons 5th Edition, you probably do the same formulas repeatedly: ability modifiers, proficiency scaling, attack bonuses, spell save DCs, and hit percentages. This calculator dnd 5e tool condenses that math into one place so you can focus on decisions, not arithmetic.
It is useful for players making a new build, DMs balancing encounters, and anyone comparing options like “longsword vs. cantrip” or “normal roll vs. advantage.”
Core 5e Formulas Used
1) Ability Modifier
Ability modifier is calculated from your ability score:
- Modifier = floor((Ability Score - 10) / 2)
Examples: 8 = -1, 10 = +0, 12 = +1, 16 = +3, 20 = +5.
2) Proficiency Bonus by Level
Proficiency increases in tiers:
- Levels 1–4: +2
- Levels 5–8: +3
- Levels 9–12: +4
- Levels 13–16: +5
- Levels 17–20: +6
3) Attack Bonus and Skill Bonus
Attack and skill checks often combine ability modifier, proficiency, and situational bonuses:
- Attack Bonus = Ability Mod + Proficiency (if proficient) + Misc
- Skill Bonus = Ability Mod + Proficiency/Expertise + Misc
Expertise doubles proficiency for skill-style checks (not weapon attacks), which this page models separately.
4) Spell Save DC
Standard spell save DC in 5e:
- Spell Save DC = 8 + Proficiency Bonus + Ability Mod + Misc DC Bonus
5) Hit Probability, Advantage, and Disadvantage
This calculator determines hit chance by checking each possible d20 outcome and respecting natural 1/natural 20 rules. For advantage and disadvantage, it evaluates both dice and uses the higher or lower result accordingly.
That makes the percentages practical at the table and accurate for most optimization comparisons.
Example Build Walkthrough
Suppose you are level 5 with a 16 in your attack stat, proficient with your weapon, and attacking AC 15:
- Ability mod = +3
- Proficiency = +3
- Attack bonus = +6 (before magic/situational bonuses)
Entering those values gives a hit probability and expected damage estimate. If you then switch roll type from Normal to Advantage, you can instantly see how much damage per round you gain from effects like Faerie Fire, flanking rules (if used), or class features.
How to Use This During Session Prep
- Compare weapon setups quickly by changing average damage and flat damage modifier.
- Test how much AC increase matters for bosses and elite monsters.
- Evaluate if a buff that grants advantage is stronger than a flat +1 bonus in your current scenario.
- Estimate expected value before choosing feats, fighting styles, or multiclass dips.
Limitations to Keep in Mind
5e combat includes many layers this simple calculator does not try to model fully:
- Multiple attacks per round and on-hit riders
- Resistance, vulnerability, and immunity interactions
- Conditional crit expansions (e.g., Champion Fighter features)
- Save-for-half effects and ongoing damage
Even with those limits, this tool is a strong “first pass” calculator dnd 5e reference for fast tactical decisions.
Quick FAQ
Does this work for spell attacks?
Yes. Use your spellcasting ability score and proficiency assumptions; the attack math is the same structure.
Can I use it for skill checks?
Yes. The Skill/Check Bonus and Passive Score outputs are intended for that purpose.
Is expected damage exact DPR?
No. It is expected damage per single attack roll under your selected assumptions, not full multi-round combat simulation.