D&D 5e Monster HP & Stats Calculator

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D&D 5e Monster HP & Stats Calculator

Calculate average HP, proficiency bonus, attack bonus, spell save DC, and other key stats for D&D 5e monsters based on Hit Dice, Constitution modifier, and Challenge Rating.

Number of Hit Dice

Hit Die Size

d4 (Tiny) d6 (Small) d8 (Medium) d10 (Large) d12 (Huge) d20 (Gargantuan)

Constitution Score

Challenge Rating (CR)

0 1/8 1/4 1/2 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Primary Attack Ability Score

Spellcasting Ability Score (optional)

Calculate Results will appear here.

function dDCalc() { var hitDiceCount = parseInt(document.getElementById('d-d-hit-dice-count').value); var hitDieSize = parseInt(document.getElementById('d-d-hit-die-size').value); var conScore = parseInt(document.getElementById('d-d-con-score').value); var cr = parseFloat(document.getElementById('d-d-cr').value); var primaryAbility = parseInt(document.getElementById('d-d-primary-ability').value); var spellAbility = parseInt(document.getElementById('d-d-spellcasting-ability').value);

// Input validation if (isNaN(hitDiceCount) || hitDiceCount 500) { document.getElementById('d-d-result').innerHTML = 'Please enter a valid number of Hit Dice (1–500).'; return; } if (isNaN(conScore) || conScore 30) { document.getElementById('d-d-result').innerHTML = 'Constitution Score must be between 1 and 30.'; return; } if (isNaN(primaryAbility) || primaryAbility 30) { document.getElementById('d-d-result').innerHTML = 'Primary Ability Score must be between 1 and 30.'; return; } if (isNaN(spellAbility) || spellAbility 30) { document.getElementById('d-d-result').innerHTML = 'Spellcasting Ability Score must be between 0 and 30 (0 = none).'; return; }

// Ability modifier formula: floor((score - 10) / 2) function abilityMod(score) { return Math.floor((score - 10) / 2); }

// Proficiency bonus by CR (DMG p. 274) function profBonus(cr) { if (cr = 1; if (hasSpells) { spellMod = abilityMod(spellAbility); spellDC = 8 + prof + spellMod; spellAttackBonus = prof + spellMod; }

// Passive Perception (assumes WIS = CON for simplicity; user can note this) // XP by CR (DMG p. 275) var crXPTable = { 0: 10, 0.125: 25, 0.25: 50, 0.5: 100, 1: 200, 2: 450, 3: 700, 4: 1100, 5: 1800, 6: 2300, 7: 2900, 8: 3900, 9: 5000, 10: 5900, 11: 7200, 12: 8400, 13: 10000, 14: 11500, 15: 13000, 16: 15000, 17: 18000, 18: 20000, 19: 22000, 20: 25000, 21: 33000, 22: 41000, 23: 50000, 24: 62000, 25: 75000, 26: 90000, 27: 105000, 28: 120000, 29: 135000, 30: 155000 }; var xp = crXPTable[cr] !== undefined ? crXPTable[cr].toLocaleString() : 'N/A';

// CR display label var crLabels = {0.125: '1/8', 0.25: '1/4', 0.5: '1/2'}; var crDisplay = crLabels[cr] !== undefined ? crLabels[cr] : cr.toString();

// Format modifier with sign function signedMod(m) { return (m >= 0 ? '+' : '') + m; }

var spellRows = ''; if (hasSpells) { spellRows = 'Spell Save DC' + spellDC + '' + 'Spell Attack Bonus' + signedMod(spellAttackBonus) + '' + 'Spellcasting Ability Modifier' + signedMod(spellMod) + ''; }

var html = '### Monster Stats Summary ' + '' + 'StatValue' + 'Average HP' + avgHP + ' (' + hitDiceCount + 'd' + hitDieSize + (conMod !== 0 ? (conMod > 0 ? ' + ' : ' − ') + Math.abs(hitDiceCount * conMod) : '') + ')' + 'HP Range' + minHP + ' (min) – ' + maxHP + ' (max)' + 'Hit Die Sized' + hitDieSize + '' + 'Constitution Score / Modifier' + conScore + ' / ' + signedMod(conMod) + '' + 'Challenge Rating' + crDisplay + '' + 'Proficiency Bonus' + signedMod(prof) + '' + 'XP Award' + xp + ' XP' + 'Primary Ability Score / Modifier' + primaryAbility + ' / ' + signedMod(primaryMod) + '' + 'Attack Bonus' + signedMod(attackBonus) + '' + spellRows + '';

document.getElementById('d-d-result').innerHTML = html; }

#### Formulas Used

Ability Modifier: ⌊(Ability Score − 10) ÷ 2⌋

Average HP: (Number of Hit Dice × Average Die Value) + (Number of Hit Dice × CON Modifier) where Average Die Value = (Die Size + 1) ÷ 2 e.g., 5d8 + CON: average d8 = 4.5, so 5 × 4.5 + 5 × CON modifier

HP Range: Min = (Dice Count × 1) + (Dice Count × CON Mod)  |  Max = (Dice Count × Die Size) + (Dice Count × CON Mod)

Proficiency Bonus by CR: CR 0–4 = +2 | CR 5–8 = +3 | CR 9–12 = +4 | CR 13–16 = +5 | CR 17–20 = +6 | CR 21–24 = +7 | CR 25–28 = +8 | CR 29–30 = +9

Attack Bonus: Proficiency Bonus + Primary Ability Modifier

Spell Save DC: 8 + Proficiency Bonus + Spellcasting Ability Modifier

Spell Attack Bonus: Proficiency Bonus + Spellcasting Ability Modifier

#### Assumptions & References

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