To calculate challenge rating in 5e, you need to consider both the defensive and offensive statistics of a creature. A creature with a 1/8 challenge rating (CR) typically has an AC of 13, 7-35 hit points, and a +3 attack bonus. Compared to a CR 10 creature, which has an average of 17 AC, 206-220 hit points, and a +7 attack bonus.
On page 274 of the Dungeon Master’s Guide, you can find a table that shows the various defensive and offensive elements that go into determining a creature’s monster rating:
— Defensive — | — Offensive — | ||||||
---|---|---|---|---|---|---|---|
CR | Xp | +Prof. Bonus | AC | Hit Points | Attack Bonus | Damage/Round | Save DC |
0 | 10 | +2 | 13 | 1-6 | +3 | 0-1 | 13 |
1/8 | 25 | +2 | 13 | 7-35 | +3 | 2-3 | 13 |
1/4 | 50 | +2 | 13 | 36-49 | +3 | 4-5 | 13 |
1/2 | 100 | +2 | 13 | 50-70 | +3 | 6-8 | 13 |
1 | 200 | +2 | 13 | 71-85 | +3 | 9-14 | 13 |
2 | 450 | +2 | 13 | 86-100 | +3 | 15-20 | 13 |
3 | 700 | +2 | 13 | 101-115 | +4 | 21-26 | 13 |
4 | 1,100 | +2 | 14 | 116-130 | +5 | 27-32 | 14 |
5 | 1,800 | +3 | 15 | 131-145 | +6 | 33-38 | 15 |
6 | 2,300 | +3 | 15 | 146-160 | +6 | 39-44 | 15 |
7 | 2,900 | +3 | 15 | 161-175 | +6 | 45-50 | 15 |
8 | 3,900 | +3 | 16 | 176-190 | +7 | 51-56 | 16 |
9 | 5,000 | +4 | 16 | 191-205 | +7 | 57-62 | 16 |
10 | 5,900 | +4 | 17 | 206-220 | +7 | 63-68 | 16 |
11 | 7,200 | +4 | 17 | 221-235 | +8 | 69-74 | 17 |
12 | 8,400 | +4 | 17 | 236-250 | +8 | 75-80 | 18 |
13 | 10,000 | +5 | 18 | 251-265 | +8 | 81-86 | 18 |
14 | 11,500 | +5 | 18 | 266-280 | +8 | 87-92 | 18 |
15 | 13,000 | +5 | 18 | 281-295 | +8 | 93-98 | 18 |
16 | 15,000 | +5 | 18 | 296-310 | +9 | 99-104 | 18 |
17 | 18,000 | +6 | 19 | 311-325 | +10 | 105-110 | 19 |
18 | 20,000 | +6 | 19 | 326-340 | +10 | 111-116 | 19 |
19 | 22,000 | +6 | 19 | 341-355 | +10 | 117-122 | 19 |
20 | 25,000 | +6 | 19 | 356-400 | +10 | 123-140 | 19 |
21 | 33,000 | +7 | 19 | 401-445 | +11 | 141-158 | 20 |
22 | 41,000 | +7 | 19 | 446-490 | +11 | 159-176 | 20 |
23 | 50,000 | +7 | 19 | 491-535 | +11 | 177-194 | 20 |
24 | 62,000 | +7 | 19 | 536-580 | +11 | 195-212 | 21 |
25 | 75,000 | +8 | 19 | 581-625 | +12 | 213-230 | 21 |
26 | 90,000 | +8 | 19 | 626-670 | +12 | 231-248 | 21 |
27 | 105,000 | +8 | 19 | 671-715 | +13 | 249-266 | 22 |
28 | 120,000 | +8 | 19 | 716-760 | +13 | 267-284 | 22 |
29 | 135,000 | +9 | 19 | 760-805 | +13 | 285-302 | 22 |
30 | 155,000 | +9 | 19 | 805-850 | +14 | 303-320 | 23 |
Here’s how to use that table:
Dungeon Master’s Guide, page 274-7
Expected CR | Resistance HP Mod | Immunity HP Mod |
---|---|---|
1-4 | x2 | x2 |
5-10 | x1.5 | x2 |
11-16 | x1.25 | x1.5 |
17+ | x1 | x1.25 |
Feature | Effect on CR |
---|---|
Aggressive | Increase the monster’s effective per-round damage output by 2. |
Ambusher | Increase the monster’s effective attack bonus by 1. |
Angelic Weapons | Increase the monster’s effective per-round damage output by the amount noted in the trait. |
Avoidance | Increase the monster’s effective AC by 1. |
Blood Frenzy | Increase the monster’s effective attack bonus by 4. |
Breath Weapon | For the purpose of determining effective damage output, assume the breath weapon hits two targets, and that the target each fails its saving throw. |
Brute | Increase the monster’s effective per-round damage by the amount noted in the trait. |
Charge | Increase the monster’s damage on one attack by the amount noted in the trait. |
Constrict | Increase the monster’s effective AC by 1. |
Damage Transfer | Double the monster’s effective hit points. Add one-third of the monster’s hit points to its per-round damage. |
Dive | Increase the monster’s damage on one attack by the amount noted in the trait. |
Elemental Body | Increase the monster’s effective per-round damage by the amount noted in the trait. |
Enlarge | Increase the monster’s effective per-round damage by the amount noted in the trait. |
Fiendish Blessing | Apply the monster’s Charisma modifier to its actual AC. |
Frightful Presence | Increase the monster’s effective hit points by 25% if the monster is meant to face characters of 10th level or lower. |
Horrifying Visage | Increase the monster’s effective hit points by 25% if the monster is meant to face characters of 10th level or lower. |
Innate Spellcasting | The impact that Innate Spellcasting has on a monster’s challenge rating depends on the spells that the monster can cast. Spells that deal more damage than the monster’s normal attack routine and spells that increase the monster’s AC or hit points need to be accounted for when determining the monster’s final challenge rating. |
Legendary Resistance | Each per-day use of this trait increases the monster’s effective hit points based on the expected challenge rating. |
Magic Resistance | Increase the monster’s effective AC by 2. |
Martial Advantage | Increase the monster’s effective per-round damage by the amount gained by this trait. |
Nimble Escape | Increase the monster’s effective AC and effective attack bonus by 4 (assuming the monster hides every round). |
Pack Tactics | Increase this monster’s effective attack bonus by 1. |
Parry | Increase the monster’s effective AC by 1. |
Possession | Double the monster’s effective hit points. |
Pounce | Increase the monster’s effective damage for 1 round by the amount it deals with the bonus action gained from this trait. |
Psychic Defense | Apply the monster’s Wisdom modifier to its acual AC if the monster isn’t wearing armor or wielding a shield. |
Rampage | Increase the monster’s effective per-round damage by 2. |
Regeneration | Increase the monster’s effective hit points by 3 * the number of hit points the monster regenerates each round. |
Relentless | Increase the monster’s effective hit points based on the expected challenge rating: 1-4, 7 hp; 5-10, 14 hp; 11-16, 21 hp; 17 or higher, 28 hp. |
Shadow Stealth | Increase the monster’s effective AC by 4. |
Spellcasting | The impact that Spellcasting has on a monster’s challenge rating depends on the spells that the monster can cast. Spells that deal more damage than the monster’s normal attack routine and spells that increase the monster’s AC or hit points need to be accounted for when determining the monster’s final challenge rating. |
Stench | Increase the monster’s effective AC by 1. |
Superior Invisibility | Increase the monster’s effective AC by 2. |
Surprise Attack | Increase the monster’s effective damage for 1 round by the amount noted in the trait. |
Swallow | Assume the monster swallows one creature and deals 2 rounds of acid damage to it. |
Undead Fortitude | Increase the monster’s effective hit points based on the expected challenge rating: 1-4, 7 hp; 5-10, 14 hp; 11-16, 21 hp; 17 or higher, 28 hp. |
Web | Increase the monster’s effective AC by 1. |
Dungeon Master’s Guide page 280-1
I create a monster with the following statistics:
AC | Hit Points | Attack Bonus | Damage/Round | Save DC |
---|---|---|---|---|
15 | 135 | 6 | 25 | 14 |
It also has resistance to nonmagical weapon damage and the Avoidance feature.
Here’s how to calculate its CR: