CR Calculator

Instructions

1. Enter expected CR of creature.
2. Fill in the HP, AC, and other defensive attributes of creature.
3. Fill in offensives attributes of creature. DPR is averaged over three rounds!
4. Click which special Monster Features it has.
5. Done!

Be sure to read the Dungeon Master's Guide section on monster creation, pages 273 through 283. You can click on the table to the right to fill in values for a given and adjust to taste. You can hover over the individual labels for a short description of how each attribute contributes to a monster's CR.

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Expected CR: CR calculation begins by determining what you want the final CR of the monster to be.

Monster Statistics by Challenge Rating

CR	Prof. Bonus	Armor Class	Hit Points	Attack Bonus	Damage/Round	Save DC

Defense

Hit Points A creature's hit points determine its defensive CR before it is adjusted by its AC.
Armor Class A creature's AC adjusts its defensive CR.

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Size: A creature's size determines the size of its individual hit dice. Tiny Small Medium Large Huge Gargantuan
Hit Dice: Unlike player characters, the number of hit dice an NPC gets is completely arbitrary. Adjust this amount to taste. d8
Constitution: A creature's HP is increases by its Constitution modifier for each hit die it has.

Vulnerabilities: If a creature is vulnerable to common damage types (especially bludgeoning, piercing, and slashing damage), its effective hit points are halved.
Resistances/Immunities: A monster's HP is multiplied based on the resistances and immunities has to common damage types (non-magical budgeoning, piercing, and slashing chief among them). None Resistances Immunities
Flying at CRs 0-9: A monster’s effective AC is increased by 2 if it can fly and deal damage at range, though only if its expected challenge rating is 10 or lower.
Save Proficiencies: Increase a creature's effective AC by 2 if it has 3 or 4 saving throw proficiencies, or by 4 if it has 5 or 6. 0-2 3-4 5-6

Offensive

Damage Per Round A creature's damage per round (DPR) determines its offensive CR, which is offset by its attack bonus or save DC. DPR is determined by averaging its maximum damage output (taking the average of dice rolls, ignoring crits and accuracy) over three rounds. Areas of effect are treated as though they hit two creatures, which fail any involved saving throws.
Attack Bonus/Save DC A creature's attack bonus or save DC adjuts its offensive CR.
Use Saves? If a creature's damage output is more dependent on save-based abilities, its save DC is used for adjusting its offensive CR instead of its attack bonus.

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