HP Cost for Magic?

How could you regulate spell-casting in a classless ruleset without doing something like Knave (1 spellbook per spell, and each spellbook can be used once per day) or Cairn (casting a spell fills an inventory slot with fatigue)? What if I feel like Knave is kind of too restrictive, and don't want to fiddle with inventory slots like Cairn does? Something that is not specific to magic, and something that is not too complicated, and something that doesn't introduce a new subsystem? Maybe spend hit points to cast a spell.


So, this is not anything new per se. Whitehack does it. I just don't particularly care for how it does it. Let's go over it anyway, so at least I can say I've considered it. Spells (or, rather, miracles) are cast by members of the "wise" class by spending hit points. However, spells are not hard-coded; a wise character has access to themes, so to speak, and negotiates the hit point cost of performing a miracle for a certain theme with a certain magnitude of impact. Below are the four possible cost categories:

  • Trivial (0): Barely matters.
  • Simple (1): Could be achieved without magic, but you're kinda lazy.
  • Standard (2): Typical fantastic effects like force fields, telekinesis, or invisibility.
  • Major (1d6): "A major breach of natural law", like teleporting someone or raising undead.
  • Powerful (2d6): "Use of raw power", whatever that means. Resurrection and weather control.

Mostly, I don't care for the random roll. It feels like it introduces granularity of cost without granularity of effect. It also feels like it obscures the actual cost of the effect; it is likely entirely intentional that magic is risky and uncertain and dangerous because that's a whole vibe, but I just prefer working with known parameters.

Actually, No!

So, how about something without dice-rolling that might even interface with traditional spell-casting systems as well as level-less ones, like the optional spell list in Knave? Here's my pitch: spend 1 HP per spell level.

This means that when you're looking at something like the OD&D spell list, which is divided into six levels, you're going to spend anywhere from 1 to 6 hit points on casting a spell.

Meanwhile, if you're looking at a level-less spell whose effects scale to the character's level (e.g. "You levitate 1" into the air per character level"), you can basically scale the effect based on how much you want to spend. This is similar to Whitehack but, again, with known quantities.

Errant has some guidelines for spell efficacy based on the character's level, and I think they're good guidelines for in general:

  • 1d6 hit points of damage per level.
  • 1d3 hit points healed per level (in Errant, 1d6 per two levels).
  • Affect 10' in diameter per level.
  • Affect 1 target per level.
  • Cast up to 20' away per level.
Maybe another good factor could be duration, like 1 combat round or 1 exploration turn per level depending on when one might expect the spell to be used.


What I'm particularly interested in is the impact this has on a magically-inclined character's hit points versus a non-inclined character. It's a convention that spell-casters in classed games are glass cannons, having less hit points in exchange for more powerful abilities. If characters have on average the same hit points, but one spends hit points to cast magic, wouldn't the outcome be pretty similar—except as the result of player behavior and strategy, rather than as a categorical distinction? Give or take, what percent of hit points would someone be willing to spend on magic?

Something I also think would be interesting is if this interfaced with a rule similar to Knave, that you have to pick between expending a scroll's magic or spending hit points in order to keep the scroll after using it. Imagine not only that, but if the ability to spend hit points was a feat rather than something inherent to scrolls and magic, so that way you don't have to fiddle with it if you don't want to (basically, a similar decision as choosing between a magical or non-magical class, but one made piecewise about your character instead of putting them in a specific box). Being able to opt out of potentially complex subsystems feels important to me, since it would save me (and others) a lot of trouble as a player from information overload. Also maybe a good instance of exception-based design.

I also mention being able to scale the effects of level-less spells which usually scale to character level, but I think it would be just as interesting to find scrolls in the wild with the same spell but of a different level. Like, cool, this is a level 1 fireball scroll, but that's less fun than a level 6 fireball scroll would be. That's good treasure!

Some spells may totally have non-scalable effects, though, and in that case maybe it would be appropriate to compare the impact to a spell from OD&D or to use a magnitude table like in Whitehack to adjudicate the cost. Still pretty flexible!

So, to summarize: After casting a scroll's spell, it evaporates (or whatever); however, if you have the Wizard feat, you can spend hit points equal to its level to keep the scroll and its magical ability. Maybe restrict it to certain schools, like Illusion Wizard.


  1. As you said, this is not anything new, but I suggest looking back much farther than Whitehack. Tunnels & Trolls (1975) uses STR as power for spells (with CON being hit points). The Fantasy Trip's Wizard system (1978) powers spells with ST, which is also Hit Points. Both of these systems also have spell-specific prerequisites, too. Fighting Fantasy (early '80s) powers spells with Stamina, which are also hit points. Reported early house rules did similar things. For example, the CalTech variant of D&D called Warlock! (developed 1975 onward) takes HP+Level+[INT modifier] as Spell Points (but you don't spend HP directly for spells). These rules have been used successfully for decades, so why shouldn't they work now? Change one thing like this and it changes player strategy, but that's to be expected.

    1. hi tom, thanks for the short history! i imagined spenidng HP in itself is not a particularly unique solution; it feels like a very intuitive way to consolidate game systems and keep track of less things. but i'm glad to know it's a method corroborated by past players!

  2. I've played around with this idea for Druids as a way of distinguishing them from Vancian wizardly magic and (potentially) more free-form Cleric miracles.

    The only snag I hit was healing magic - if it costs less to heal HP than to cast the spell, you can have two characters with that ability and they just heal each other up constantly for no net cost. The solution is pretty simple, though - if healing magic is going to be available to a character with this spellcasting style, just make an exception that healing magic costs HP equal to the amount healed. Bada Bing Bada boom.

    1. it's neat to distinguish druids that way! :) it is kinda weird for healing magic; IIRC whitehack just doesn't allow mages to be healed magically at all, which just feels kind of restrictive.

      treating it basically as 'gifting' HP is really interesting! my first thought was that it wouldn't be strong enough, but that actually works really well in a "gritty" context, like if you're healing someone to stabilize them from dying as opposed to like "now you're back at 50% hp and back in the game!"

    2. I tweaked Whitehack to have spells inflict spellburn instead of standard damage. So Wise characters still recover HP the same as everyone else but you can't heal spellburn with magic or potions or whatever. If HP<spellburn the Wise might die.

    3. ! that is an elegant solution! especially because my hunch would be, "oh, i wish i could have a separate pool of hp and magic points, but that's two things to track..."

      having two "damage pools" instead is very clever and intuitive!!

    4. Yeah, it doesn't feel like more work because you don't have to add them. Spellburn counts up, HPs drop down, when they cross start rolling death saves (or whatever your system does when you run out of HP)

    5. i am so enamored with that -- so elegant/intuitive!! :) do you have a post about it anywhere if i ever want to share or cite it in the future? that just changed the game for me

    6. ah, i didn't realize it came from DCC -- though i like yours a lot better, since 'losing' hp feels more intuitive than ability scores. thank you again for sharing!!

    7. The only similarity with DCC (afaik) is the name. "Spellburn" is more evocative and specific than "Fatigue".

      The last time I wrote up my Whitehack houserules was 2019, they need updated again, but they do have the magic/HP fix. https://ominosity.wordpress.com/2019/10/30/whitehack-updated-houserules/

  3. I can never resist the urge to point out that the Lord of the Rings Adventure Game has many quality of life OSR improvements that I didn't see in games again until the twenty-teens, including HP for spells.

  4. HP-draining casting was tested and works perfectly well in "Into the Dungeon: Revived"


    > Casting a Prepared Spell as an action causes Spellburn Damage to the caster equal to 2hp per
    Spell Circle ignoring Armour. At 0hp, Spellburn targets WIL instead of STR: pass a WIL Save to avoid Critical Spellburn or be Stunned for the next turn.

    > Each time you take Mystic Feature, choose an additional Signature Spell to cast without preparation and at half its cost (1hp per Spell Circle).

    1. i am so glad you brought up ITDR because the more i hear about it, the more it sounds specifically made for me -- everything i hear about it is what my ideal d&d would be like, or what i imagine the perfect version of d&d to be 😂 it even has five levels and feats! i am so delighted to keep looking into it and maybe try it out, though i would still want to trim some things maybe


    3. Yep, hello there! 👋

      Glad my intention of creating a rules-lite D&D-like game came through =)

  5. I'm super interested in the undercurrent of unlocking access to magic in a more a la carte manner rather than "you are a caster" or "you are not a caster". I can imagine raising the amount of HP one can spend to keep a spell, and thus the level of spell retainable, with experience, along with other variations based on type of effect or whatnot as you described. Plus add-on abilities to reduce HP costs when conditions are met, or trade other effects against it (fatigue? sacrifice GP? I don't know).

    Another option for limiting healing magic is to steal the idea of System Strain from Crawford's xWN games. Something I like about that is that it can be applied as written to limit the amount of healing any one character can receive or could be applied to the caster to limit the amount of healing any one character can give, and in the latter case could be applied to other spells that you might want to put soft limits on.

    1. totally agree! like i can imagine there not just being different expenses, but also different methods entirely of spellcasting that (like you said) can be acquired a la carte rather than from different classes. e.g. a vancian spellcaster who can spend time to memorize the contents of spells until they cast them or go to sleep, or a character who has both this and the HP expense as options as their disposal.

      system strain is a really clever idea! i like how brian used a similar idea above, having a special kind of "damage" that cannot be healed. :)

  6. A similar idea I've often toyed with is letting characters trade HD (or max HP) at character creation for magic dice (or spell slots, mana points, whatever your system's equivalent is.) It's a similar way of creating "squishy casters", but I'm not sure whether I prefer the fact that your version moves the decision-making from character creation to play time or not... it's a nice dilemma, but it also means the wizard starts the adventure just as tough as the fighter, which seems off.

    I guess you could also try a compromise: at any time, a spellcaster can permanently sacrifice max HP to permanently increase their spell points/spell slots/magic dice/etc (which refresh when they rest as normal.) So the guy who's dipped into spellcasting can push themselves past their limits to save the party in a pinch, but they'll be forever changed and more wizard-y than before.


Post a Comment

Popular posts from this blog

Plagiarism in Unconquered (2022)

OSR Rules Families

Bite-Sized Dungeons