Skill-Based Energy Costs For GURPS Magic

by Robert Neal Byles

Art by Dan Smith and Colored by Keith Johnson

Energy costs for casting spells in GURPS Magic follow a very simple, linear rule: "Each spell has an energy cost. When you cast a spell, it costs you energy—either HT or ST. The better you know a spell, the less energy is required to cast it. If you know it well enough, you can cast it at no cost." (GURPS Magic, 2nd, Ed., p. 8) This is a well-reasoned explanation; however some have always felt that the implementation of this statement in the rules was somewhat limited. Energy cost drops by 1 point at Skill 15 and by 1 additional point for every 5 Skill Levels after that. This is simple, yes, but not only is it rather static, it tends to result in cookie-cutter mages; how many mages exist with an IQ 14 and Magery 3 so that all of their M/H spells are at 15?

Currently, each player knows how much it is going to cost him before he casts the spell, every time. This lacks the danger and uncertainty (beyond the possibility of a Critical Failure) that fantasy literature often ascribes to mage-craft. Furthermore, a character gets a fair boon at Skill 15 but has little motivation to improve from there, other than to power-spend her points until she reaches Skill 20 and the cost goes down another point. Again, this leads to cookie-cutter mages with skills levels that tend to jump in five point increments.

The following system takes the above statement about the connection between energy cost and skill and adds a third factor: how well the caster concentrates and performs the necessary rituals for the spell. Or, to put it more basely, how well the player rolls the dice. The net result is that, with lucky rolls, a mage's spells can cost him significantly less than they do under the official system. This is balanced by the addition of a further element of risk. A failed roll no longer costs a mere 1 point in energy but will usually cost the mage more than it would have had the spell succeeded.

Energy Cost of the spell, as listed in the spell descriptions, remains as the Base Cost of the spell. This is then modified by the relative success (or failure) of the die roll to the spell caster's skill level, as well as the mana level of the region. The number by which the skill roll succeeds is the Level of Success and is negative in the case of a failed roll. This will yield either a positive modifier to the base cost (more energy), a negative modifier to the same (less energy) or no modifier at all, according to the following table.

Level of

Energy Modifier


Low Mana



Very High

Crit Failure      +5+3+2+1
-9 to -6+4+2+1 Base Cost 
-5 to -2+3+1 Base Cost -1
-1, 0 or 1+2 Base Cost -1-2
2 to 3+1-1-2-3
4 to 5 Base Cost -2-3-4
6 to 7-1-3-4-5
8 to 9-2-4-5-6
Crit Success-3-5-6-7

This is, of course, in lieu of the deductions to cost as they are now written. (Thus the minus 1 point at skill level 15, 2 at 20, etc, no longer apply.) Assuming normal-mana, both a success by 10 or more and a Critical Success, regardless of the amount by which it succeeds, are always -5. Likewise, Critical Failure and failure by 10 or more are always +3. Adjustments to rituals and casting time due to high (or low) Skill Level remain as described in Magic.

Skill-Based Energy Costs For GURPS Magic

If a mage wishes to maintain a spell beyond its normal duration, cost to do this is determined based on one of two choices made by the mage. She can either use the energy cost based on the initial casting roll, or she can roll again hoping for a better result. Whatever the new result, the mage is obligated to pay it. She does not have the option of letting the spell lapse rather than pay a higher cost to maintain. Note that only a critical failure at this stage will negate the spell. A normal failure will result in a higher energy cost to maintain but the spell will continue to function as per the original casting.

Example: Sir Seamus casts a Shield spell on Sir Fenris, a fellow Templar Knight, increasing Fenris' Passive Defense by 4. Due to Fatigue, Seamus' ST is currently 9. Shield costs 2 energy per bonus (half that to maintain) for a base cost of 8/4. Seamus rolls a 9, which is 4 less than his skill level of 13. The Energy Modifier is -2 so his spell costs him 6 points. A minute later the battles rages on. Seamus maintains the spell for another minute but as his remaining ST is only 3 he knows that 3 more points for maintaining the Shield (half the cost of the initial casting) will knock him out (down to 0 ST). He decides to trust in God and try a new roll. Seamus rolls a 15, 2 more than his skill! This results in an Energy Modifier of +1, bringing his base cost to maintain (4—half the original base) up to 5. His last three points of ST are depleted and he takes 2 hits of damage from his HT before passing out cold! Fenris, however, keeps his +4 PD for another minute and manages to win the day. The Lord works in mysterious ways . . .

If a spell is cast using a Powerstone or Manastone and the Stone is depleted in the casting, the overage is drawn from the caster's ST as fatigue. If the caster's ST is depleted in the casting, the mage passes out, and any overage comes directly off of HT as injury! This only flows one way. In other words, energy that exceeds a character's ST cannot be transferred to available Powerstones, nor can overage to HT be diverted to Powerstones or ST. However, the player may announce a split between various sources of power (ST, HT or Powerstone) before the casting. These should be in percentages rather than actual number of points, using quarters, halves, and thirds. Remainders should be split as evenly as possible with any remainders going to the selected source that is highest in the list. That is, Powerstones first, ST second and HT last, but only if such a source was indicated. Thus, if a player chose to split the cost between ST and HT, the remainders would go to ST, and not to any Powerstones he might be carrying.

Example: Ebonan casts a 3-hex Mass Sleep spell (base cost of 9). Prior to casting he decides that three-fourths of the cost will draw from his ST while the remaining quarter will come from the Powerstone in his staff. If he succeeds by 4 then the spell costs him 7 points. 3 points are deducted from his ST (three-fourths of 7, rounded down) and 1 point comes off of his Powerstone (one-fourth, rounded down). What's left is split, with 1 point taken from each and the final point coming off of the Powerstone. The end result then is 4 points from ST and 3 from the Powerstone.

As noted above, this system gives mages the advantage that their spells, if they are good at them, should cost significantly less to cast, while sometimes costing nothing at all. The disadvantage is that they will sometimes cost more, and failures will be terribly expensive. This adds a random element to the game which will make running mages more dangerous and difficult, but also more realistic and fun. If Corenth is down to 3 Fatigue but needs to bring off that last 3-dice Fireball to save the day, does he risk it? If he succeeds by 2 or more, he's golden (if rather exhausted), but if he fails he passes out. If, however, Corenth succeeds by zero or one, the Fireball goes off as expected the instant before he blacks out. Corenth is our hero!

Differing mana levels will shift this table in one way or the other as shown. This system chooses to ignore the low-mana modifier to skill level on the grounds that this system restricts spell casting in low-mana areas enough, but this is entirely up to the GM. Magic items that require a roll and/or an energy cost will cost the listed amount, regardless of the roll or the Power of the item.

Most of the spells in Magic and Grimoire function under this system with no necessary modifications. A possible exception to this is the Recover Strength spell. While Recover Strength can work as is, this system suggests an intriguing alternative. Rather than treat Recover Strength as a form of Advantage, as it does in the official description, this system treats it more like a Skill, complete with ritual and die roll.

Recover Strength


Works on the caster himself; cannot restore ST to others. Allows the caster to recover fatigue by "tapping into" the local ambient mana to "recharge," as it were. The caster must rest quietly for the necessary casting time but may maintain ordinary spells so long as they do not require concentration. Note that Recover Strength is the only spell with a Base Cost of 0 as well as the only spell that can yield a negative Energy Modifier.

With a Base Cost of 0, a success by 5 would yield a net result of -2 energy cost. This means that the caster would regain 2 points of lost Fatigue. Similarly, a failed casting of Recover Strength can result in a loss of ST. Thus, a failure by 4 would yield a +1 modifier and actually cost the poor mage a point of ST. Note that Recover Strength can be cast in a low-mana area (but not a no-mana area, obviously) assuming the caster is willing to risk it.

This spell may only be cast once every ten minutes in the same 10-hex radius location, regardless of who casts it. That is, a mage must either wait for ten minutes or move to a new location before casting this spell again, and two mages may not cast the spell if they are within 10 yards of each other. This is because the spell channels the local mana into the mage, which temporarily depletes the area. In low-mana zones this is thirty minutes and thirty yards, respectively. In high-mana areas this is five minutes and five yards, and in very high-mana areas minutes and yards are both two.

Duration: Permanent.
Base Cost: 0.
Time to Cast: 1 minute.
Prerequisite: Magery; Lend Strength
Item: Jewelry. Recharges the wearer's ST at the rate of 1 per minute assuming she can move around enough to compensate for the 10-hex radius restriction; always on. Automatically interferes with the use of Recover Strength spells, by the wearer or others, within its area of effect. Interferes with Powerstones as well as if it was a Powerstone itself—it is always considered to be the "largest stone" in the area. This item would be exceedingly rare. Energy cost to create: 1500; must be made of alloyed gold and platinum (minimum value of a small ring $500).

Article publication date: November 10, 2000

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