DnD Combat Encounter Difficulty

One of the things I see new DMs struggle with is how to determine combat encounter difficulty.  The Basic Rules cover this topic.  They don’t seem to give DM’s a lot of confidence, though. Because of this I think its worth covering them again.  Here’s what I have to tell you at the outset:  If you follow the rules for encounter creation, you’ll almost never need to worry about the risk of killing all of your players.  The one exception is at level 1. Level one PCs are very fragile.  Handle with care.

The way encounter difficulty is explained in the Basic Rules ends with you comparing the difficulty of the creatures you’ve selected for the encounter to what the players can handle. I feel like this is a little counterintuitive. Why select the monsters first and then see if they fit?  I think you’re better of determining the difficulty range of the combat first, and then choose the monsters to fill the budget.  Here’s how I approach it:

1. Figure out how hard you want the combat to be.  What is the purpose of the combat encounter?  Is this just a little scuffle, or is it a boss battle? The basic rules provide four levels of difficulty: easy, medium, hard and deadly.  Easy encounters should be few and far between.  They’re barely worth spinning up all the combat mechanics for.  Deadly encounters should also be rare, save them for boss battles and the like.
2. Calculate the Experience Point budget for the battle.  Multiply the number of PCs by the XP budget for the desired difficulty level and the next level up using this table from the basic rules.
3. Determine the number of creatures you want to use in the battle.  This will determine the modifier  See the table below.  I recommend keeping the battle between 1 and 6  total creatures fighting against your party.   1 monster lets you have the full XP budget.  For two, divide the budget by 1.5.  For 3-6 monsters, cut the budget in half. I wouldn’t go much further than that…
4. Now that you have the ranges, you can plug in the monsters.

Encounter Difficulty Example calculations

1. Determine Encounter Difficulty – In my experience, there’s not a lot of reason to create a battle that is below the Hard difficulty.  I think the difficulty of an encounter is generally overstated for by the names of the encounters. 
2. Lets assume we’ve got 4 level 2 PCs.  For a hard encounter the budget per player is 150, for deadly it’s 200, so your range is 600 to 800 xp for the budget.
3. I want this to be a bit of a tactical battle, with the players up against 3-6 monsters, instead of them facing off against one big nasty.  Let’s say it’s a run-in some soldiers.  Because of the number of monsters, I divide the range by 2.  I can choose enough monsters to fill a budget between 300 and 400 xp
4. I can have 3 thugs at CR ½ (100 xp) in my encounter. 

I think taking the number of creatures in the combat into account first makes these calculations a lot more intutitive.  That way, I don’t have to worry about whether or not each additional creature I choose is going to tip the scales and jump the difficulty of the encounter way beyond the range I want it to be in.

Here are some great monsters to plug into that calculation!