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Rolling Lots of D20s? Assume One Quarter Succeeds

by Mike on 20 January 2025

When you need to adjudicate a whole bunch of checks — say rolling two dozen saving throws for a bunch of skeletons hit with Turn Undead — simplify the situation by assuming one quarter succeeds.

This quick rule-of-thumb is part of the Running Hordes section of the Lazy DM's Companion but it's a good tool to keep in our toolbox for lots of situations. Sometimes you need to roll a bunch of attack rolls against a single character. Sometimes you need to roll a big pile of ability checks. Sometimes you need a big group to make a bunch of saving throws.

Assume one quarter succeeds.

You can slide this scale up or down depending on the situation. If the creatures making the checks have advantage, assume half succeeds. If they're at disadvantage, assume it's one on ten. This calculation also works if the target number the roller would have to shoot for is particularly high or low. Keep the math easy.

If you want to add some variance, subtract three from the number of successes and add 1d6. This change shakes things up and shows players that there's some variance to the result instead of what feels like an arbitrary number.

This "one quarter succeeds" guideline is based on the idea that the creatures making the check need to roll a 16 or better to succeed. It assumes these creatures are generally weaker than the character they're attacking or the spell they're saving against. It's a skeleton (+4 to hit) versus an armored paladin (AC 20). Many times this guideline is in the favor of the characters (and the players) which makes it easier to accept.

Assuming one quarter succeeds lets you abstract lots of dice rolling and get back into the fiction and action in the world. Instead of rolling two dozen saving throws you get to say:

"Eighteen of the twenty four skeletons surrounding you are destroyed as your waves of radiant light turn them to dust! The remaining six claw forward and attack!"

If you're looking for more tricks for running hordes of monsters against the characters, check out Running Hordes: The Lazy Way to Run Lots of D&D Monsters.

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Each week I record an episode of the Lazy RPG Talk Show (also available as a podcast) in which I talk about all things in tabletop RPGs.

Last Week's Lazy RPG Talk Show Topics

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Last week I also posted a couple of YouTube videos on Distance, Reaction, and Activity Rolls for Random Encounters and The Puzzle box – Dragon Empire Prep Session 9.

RPG Tips

Each week I think about what I learned in my last RPG session and write them up as RPG tips. Here are this week's tips:

Choose monsters that fit the story and environment. Wrap them in historical lore.
Swarm characters with lots of one- or two-hit low CR monsters. Let players enjoy their big area blasts.
Include big brutes in battles who are intended to be banished or controlled.
Give magic weapons or suits of armor a cool name, theme, history, and daily-use spell effect.
Let mechanists and artificers understand how magical artifacts and arcane machines operate.
Roll on behalf of characters attempting to detect traps so they don't know if they failed or if there was never a trap to begin with.
Include several ways for characters to traverse a dungeon – vertical chutes, deep cracks, collapsed elevators, and so on.

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