A {{Stock RPG Spell|s}} whose damage is proportional to the target's current HP; the most common forms will reduce the opponent's HP by 1/4 (or 1/2) of its current value, weakening the target without killing it.

Like a FixedDamageAttack, these attacks ignore the game's usual damage calculations altogether, with the only variable being whether or not the attack actually ''hits'' the target to begin with.

Naturally, a character at full HP will receive the most raw damage, while characters with low HP will receive hardly any whatsoever. Whether or not this attack is capable of actually ''landing'' the killing blow varies by system: The amount of damage inflicted is typically rounded down, so a character reduced to their last HitPoint might receive no damage whatsoever (unless ScratchDamage is required, or if ElementalRockPaperScissors gives it a boost).

Sadly, most Percent Damage Attacks become a UselessUsefulSpell in the hands of the player: Despite that [[HealthDamageAsymmetry enemies have more HP than the heroes]] (meaning the attack can inflict greater damage), enemies will frequently evade the attack or simply be resistant to them ([[TheComputerIsACheatingBastard as a rule]]), and Bosses have ContractualBossImmunity against it or have large enough HP pool that any damage the spell does to them usually ends up being {{cap}}ped, meaning they're not any more effective than any other single-hit spell or attack that hits the cap as well.

An occasional variant is a FixedDamageAttack calculated using a percentage of the target's ''maximum'' HP, rather than their ''current'' HP.

Compare HPToOne, a more extreme attack that removes all ''but'' the last HitPoint from its target. If the damage percentage is 100% then you have a OneHitKill.
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!! Examples

!! Role-playing games
* The ''FinalFantasy'' series has many examples and frequently classifies them as a "gravity" element, featuring versions that remove 25%, 50%, and 75% of the opponent's HP, respectively. Some can target multiple foes simultaneously, and are far more likely to succeed when used against your party members than against monsters.
** In ''VideoGame/FinalFantasyVII'', ContractualBossImmunity is avoided for some flying bosses, who only have a 50% damage reduction from it instead (including one of the two {{Bonus Boss}}es). Also, there is at least one enemy that ''absorbs'' gravity attacks as HP: Master Tonberry.
*** There was also one BossInMookClothing whose HP total was so high that gravity spells, while still effective, repeatedly hit the damage {{cap}} of 9999.
*** The FinalBoss has an attack with a spectacular animation that takes about two minutes to complete. It seems like an attack that can achieve an easy TotalPartyKill, but in fact all it does is take off 15/16 of each of your characters' current HP, so it's actually incapable of killing anyone.
** In ''VideoGame/FinalFantasyIX'' and ''VideoGame/FinalFantasyXII'', gravity-based damage was calculated based on an opponent's ''maximum'' HP rather than their ''current'' HP and therefore became a FixedDamageAttack.
** One of the first battles of ''VideoGame/FinalFantasyX'' involved an boss whose only attack was ''Demi'', which is a gravity-based attack that does damage equivalent to half of each character's current HP. Anyone who knows Achilles and the Tortoise knows this boss can't possibly kill you with this attack alone.
** ''VideoGame/FinalFantasyX2'' has both flavors of percent-based attacks all over the place.
* In ''FinalFantasyCrystalChronicles'', the "Gravity" spell could be used once per battle against a few bosses to inflict a percentage of damage. It also temporarily immobilized airborne opponents after damaging them, making them easier to defeat.
* In {{Persona 4}}, while most Light element attacks were instant kills, one attack called "God's Judgement" reduced the target's current HP by half. Being part of the Light element, it could still be nullified/reflected by an appropriate Persona.
** In ''DigitalDevilSaga'', ''most'' Hama/exorcism spells reduce HP by a percentage with a decent chance of working (both of those depending on the spell), but they will instant kill enemies weak to them (Mudo/death is always a OneHitKill).
* The "Super Fang" move in ''Franchise/{{Pokemon}}'' reduces the opponent's HP by half, and is mandated to inflict ScratchDamage if the opponent is already reduced to one HitPoint (which may not be what you want in a ''Pokemon'' game). It is not affected by the game's ElementalRockPaperScissors beyond the fact that "Ghost"-type opponents are immune to its element.
** The moves "Crush Grip" and "Wring Out" obey the standard damage formula (attack/defense power, ElementalRockPaperScissors, chances of a CriticalHit), but their base attack power is proportional to the opponent's percentage HP. If one strike reduced the opponent's HP by half, the next strike will only hit for half as much.
** In the ''VideoGame/PokemonMysteryDungeon'' spin-offs, collateral damage caused by [[ActionBomb "Selfdestruct" and "Explosion"]] was always 50% of the teammate's current HP (or if they were Fire-type, 25%).
* In ''VideoGame/SecretOfMana'' characters inflicted with "[[TakenForGranite Petrify]]" [[StandardStatusEffects status]] also lost 50% of their current HP as an immediate side effect.
** The Moon Godbeast Dolan in ''VideoGame/SeikenDensetsu3'' posessed an attack that reduces a party member's current HP by half.
* The Eclipse Dark Tome reduces the target's HP by half in ''FireEmblem''.
* In addition to various HPToOne attacks, ''VideoGame/ChronoTrigger'' features several bosses (mainly Dalton and his Golems) who use attacks that drop your health to half of its current state.
* ''VideoGame/{{Runescape}}'' has enchanted ruby bolts which have a chance to take away 20% of opponent's health from the enemy at the cost of decimating player's health. They're used to take down some of the stronger enemies.
* ''VideoGame/GoldenSun'''s summons use the target's max HP to calculate damage, but they also have a fixed base power.
* [[InvertedTrope Inverted]] in ''TalesOfMajEyal'': the Chronomancy spell "Echoes from the Past" deals damage equal to a percentage of the damage the target has already taken rather than how much HP it has left.
* Pretty much a staple of many LeagueOfLegends in several variations as below. Designed as a major tactical decision for a player, since percent damage works extremely well against characters with lots of HP but few other defenses, but is very ineffective against people with low HP that rely on healing or armor to defend themselves. Certain types of percent damage attacks are more common for certain archetypes:
** Damage set at a percent of target's current HP level, usually used by champions gearing up to kill HP tanks (e.g. Dr. Mundo's cleaver, Liandry's Torment).
** As a percentage of total HP, usually used for offensive spells to discourage buying HP in favour of resistances (With exception to Vayne, whose total HP based damage passive ability deals true damage and cannot be reduced).
** As a percentage of the caster's own HP, often owned by tank characters to encourage buying HP boosts (Sejuani, Shen)
** As a percentage of the target's missing HP, used by assassins (e.g. Kha'zix) to finish off foes one-on-one (damage increasing the longer the fight goes on instead of decreasing.)

!! Other genres
* In the first ''VideoGame/{{Civilization}}'', nukes destroyed ''exactly'' half of a town's current population, including defending units and one significant structure.
* The Sorceress in ''[[VideoGame/{{Diablo}} Diablo II]]'' has the Static Field skill, which does 25% damage to any enemy, even a boss, though some targets cannot be dropped below a certain level this way.
* ''VideoGame/{{Worms}}" has the Battle Axe in some games, which halves the target's HP.
* In ''{{DROD}} RPG: Tendry's Tale'', stepping on a hot tile takes 5% of HP; stepping through an Aumtlich beam takes 50%. Optimisation often requires leaving healing potions untaken so your HP is low when you incur the percentage attacks, then taking them afterwards.
* {{Defense Of The Ancients}} has Huskar's ultimate, named Life Break, which does this to [[CastFromHitPoints himself]] as well as his opponent, with the damage he takes being reduced as it's leveld up.
* WarcraftIII: The Death and Decay spell damages for 4% of a unit's total life per second, and lasts for 35 seconds.
** Several spells do percent ''buffing'': The Trueshot Aura increases ranged damage by 10, 20 and 30% (just 10 for the unit version), Roar gives all friendly units a temporary 25% damage increase, and Command Aura gives all units in range a 15% damage increase.
* Played with in ''VideoGame/TeamFortress2'', where the Spy's BackStab does damage equal to a certain percentage of the target's health--namely [[ThereIsNoKillLikeOverkill 600%]] of it. For most purposes this is makes it indistinguishable from a OneHitKill, but in certain conditions (most notably using the Dead Ringer) the target may have enough damage reduction that can survive the hit.

!! Other
* The word "decimate" originates from a Roman military punishment, wherein soldiers found guilty of cowardice were ordered to draw lots, with one out of every ten[[note]] "decimus" is Latin for one-tenth[[/note]] men being executed as a result. The term is [[YouKeepUsingThatWord rarely used that way any more]].
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