Before You Roll, Do the Math: A D&D Tip Inspired by Numenera

Monte Cook’s thirty-plus years as a game designer include credits co-designing third-edition Dungeons & Dragons and his science-fantasy roleplaying game Numenera, which mirrors some broad patterns of D&D. Numenera includes characters that resemble fighters, rogues, and spellcasters who gather to explore dangerous places. Players even roll d20s and aim to reach target numbers that rate a task’s difficulty. Make no mistake though, Numenera features innovations. Monte writes, “I think I have some fresh variations on some concepts that are in games now, and some wholly new ideas as well.”

For example, Monte noticed that players have more fun rolling to attack than watching a dungeon master make a foe’s saving throw. Rolling gives us an emotional sense of involvement. So in Numenera, the players always roll the dice. When players attack, they roll to hit; when monsters attack, the players roll to defend.

Letting players always roll has the side effect of eliminating the GM’s ability to fudge rolls. “If the dice don’t mean anything, then everything is predetermined, and it’s no longer a game by any definition—just a story being told,” Monte writes. “So the dice need to matter. But that means that sometimes a PC will fail when they would succeed if it were a story, and vice versa. That’s not a flaw; it’s a feature. It’s what makes roleplaying games so exciting.” Dice make roleplaying games unpredictable and dynamic. Numenera embraces that. (You may like how fudging rolls gives a GM power fit the game into a story, but Numenera gives GMs and players other tools to help shape a thrilling narrative.)

Numenera highlights the fun and drama of rolling dice in other ways. One has influenced how I run D&D and improved my games.

The rules of D&D encourage rolling first, and then adding bonuses and penalties to learn whether the roll means success or failure. The delay of calculating after the roll often robs the roll of potential drama.

Numenera puts the calculations before the roll by making things like skills and circumstances adjust the target difficulty. By the time the players throw the dice, they know exactly the number they need. Monte explains that calculating before the roll “makes task resolution–and in particular combat–move much, much more quickly if you’re not waiting for people to add together numbers (or to ensure they have all their various miscellaneous modifiers accounted for).” Even better, calculating first gives the roll an immediate significance that everyone playing understands.

Of course D&D players and DMs can calculate the target number needed for success before rolling too. Just subtract all the bonuses from the DC. As a DM, I often announce these target numbers before open rolls to wring maximum drama from a roll of the dice. As a DM under the influence of Numenera, I find myself making such announcements before nearly every roll. I’ve always rolled in the open, but when players know what the numbers mean, they pay attention and they react to the numbers.

Calculating a target number in advance hardly takes extra effort. Sure, some very low or high rolls could have skipped the math entirely. But pre-calculating often makes up for the occasional unnecessary effort in volume. If I roll a save for the 7 ghouls in a fireball and I know they need a 13 to succeed, I can toss 7 d20s and spot all the successes in an instant. If I throw the dice with just DC 15 and +2 in my head, then making sense of 7 numbers on the dice and the 2 numbers in my head takes much longer.

The most exciting moments in games like Numenera and D&D often come from die rolls. When we throw the dice, game masters and players alike surrender control to chance. For maximum drama, don’t make players wait for calculation of the results. Tell everyone the number to look for on the die.

Related: D&D and the Role of the Die Roll, a Love Letter.

Steal This Rule: Numenera and XP for Discovery

7 thoughts on “Before You Roll, Do the Math: A D&D Tip Inspired by Numenera

  1. Kristen Mork

    I’ve used approach for several years. In 5E, the math is weird. Players roll for defense: the target number is 22+attack bonus (using standard AC as a bonus to the roll) or 12+attack bonus (if you scale AC down by 10 to use smaller numbers). The same thing works for spell efficacy: the target is 22+save bonus (using standard spell DC as a bonus to the roll) or 12+save bonus.

    To justify that weird 22: if a monster has +7 to hit and the character has AC 17, the monster needs to roll 10 or higher. That happens 55% of the time. Flipping this around, the target to defend is 29. The player needs to roll 12 or higher to dodge, which happens 45% of the time, preserving the 55% chance to hit.

    The “off by two” error has two sources. One, ties are won by the roller. Two, a baseline of 10 is rounded down. If 22+AC is problematic, you can use 20+AC, which perfectly corresponds to needing to *beat* the target’s AC or spell DC. Such a shift makes attacks less useful and spells more useful. It also mirrors ability check contests where ties preserve the status quo.

  2. Backcountry164

    Love the Numenera settings but not a fan of the dice system. Rolling dice is fun, as a GM I want to participate in the game not just adjudicate over it.
    And of course with 5e there’s little reason to fudge rolls because there’s rarely any real consequences associated with failure.

  3. Joe B.

    Gosh I’m being dense. I want to try this but I think my own thinking is muddy. DM D can you give an example of what you do with a monster hitting a PC? Do you ask the PC AC?

  4. Dave Dalrymple

    Technically, D&D 2e used the “target number” approach for attack rolls (but not for ability checks). Rath is supposed to subtract any strength and weapon bonuses from his THAC0, so that the raw number on the d20 indicates a hit or a miss.

    1. 20x6

      Ability Check and Saving throws both used target numbers in 2e. Ability/proficiency checks were based on rolling under your relevant ability score. Savings throws were rolling a specific static number derived from class and HD. Powerful spells/monsters generally didn’t force more difficult saving throws.
      Thac0 is definitely built to generate quick target numbers, but does require some math upfront. TN = thac0 – Target AC.
      (I realize this is a trivial correction, but I have been on a classic D&D kick lately)

  5. Vikshade

    I got this tip from Unearthed Arcana 3e or DMG II 3e. Can’t remember which, but it definitely keeps the players more involved and hanging on the die rolls much more than me rolling behind a screen.


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