How to calculate the attack rolls and ability checks for monsters?

Question

Very new player here. Looking at the stat block of a goblin: for a shortbow attack it says +4 to hit and the goblin has a Dex modifier of +2.

Does this mean I add 6 to the d20 roll or just the 4 and ignore the Dex modifier?

Same with using Stealth. It says Skills: Stealth +6. So would I take 6 and add +2 of the Dex modifier or just add 6 to the d20 of the Stealth check roll?

Thank you!

Answer 1

Use the modifiers as written and don't add anything to them

In a monster's statblock the to hit bonus is already inclusive of any bonuses that apply including ability score. The same is true for ability checks; everything including proficiency should already be included in the statblock.

For example, you can see that the goblin's stealth skill comes from the fact that it has a +2 dex bonus and a +2 proficiency bonus which is doubled because they have expertise. Thus they have a +6 to stealth. However, you don't need to know how they are calculated, just that you use them as-is.

Thus, you just roll a d20 and add the relevant modifier as listed. Do not add the ability score mod or anything else to it.

Answer 2

Monster proficiency and player proficiency are similar

Monster manual page 8: Profiency bonus by challenge rating.

• Goblin has +2 based on its CR (1/4) just as a PC will have a proficiency based on character level: +2 at level 1-4, +3 at level 5-8, etc. (PHB p. 15).

• Goblin Dexterity of 14 gives it a bonus of +2 based on the weapons it uses, and is proficient with

  That is how the +4 to attack is arrived at:

• Scimitar has the finesse property: thus the 14 Dex (+2) of goblin is added to the to-hit for the Goblin (CR 1/4 proficiency bonus (+2))

• Attack action for scimitar already includes both +2's for a +4.

• Likewise with the short bow attack.

Don't keep adding +2's as it's already been done for you in the MM under the entry for the attacks specified for a monster.

Caution: For some skills, like the Goblin's stealth, the proficiency bonus is added twice to reflect expertise. That is why the Goblin's Stealth is +6 rather than +4. (See the entry in the PHB on expertise, Rogue player class, for this template).

Another example is the Aboleth(MM. P. 12):
CR 10 = Prof Bonus of +4.
That is why History is +12 (+4 twice for proficiency) and Perception is +10 (+4 twice for proficiency); these are added to the stat bonuses of +4 Int (History) and +2 Wis (Perception) respectively.