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.
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
- All formulas follow the D&D 5e System Reference Document (SRD) and Dungeon Master’s Guide (DMG), pp. 274–275.
- Average HP uses the statistical average of each die (e.g., d8 averages 4.5, rounded down for the total), matching the official Monster Manual notation.
- Hit Die size is determined by creature size: Tiny = d4, Small = d6, Medium = d8, Large = d10, Huge = d12, Gargantuan = d20 (DMG p. 276).
- Constitution modifier applies once per Hit Die to both average and min/max HP calculations.
- Proficiency bonus is derived from CR, not character level, as per DMG monster creation rules.
- XP values are taken directly from the CR/XP table in the DMG (p. 275).
- Spell Save DC and Spell Attack Bonus are only shown when a spellcasting ability score greater than 0 is entered.
- This calculator does not account for Legendary Resistances, Legendary Actions, or Lair Actions, which are narrative/design choices beyond stat formulas.
- Passive Perception and saving throw bonuses require knowledge of individual ability scores not collected here; use Ability Modifier + Proficiency Bonus (if proficient) for each.