If the Aid spell has been cast on a target, what happens to their current hit points when the spell ends?

Question

The 5e D&D Basic Rules v0.1 description of the second-level cleric spell Aid says (p. 83):

Your spell bolsters your allies with toughness and resolve. Choose up to three creatures within range. Each target's hit point maximum and current hit points increase by 5 for the duration.

I'm a bit confused as to what is supposed to happen to the PC's current HP when the spell ends. Obviously if it's above their normal maximum, it should fall. But do they lose 5 of their current hit points even if it's already lower than their regular hit point maximum? That seems to be what the text is saying, but that seems off to me.

It sort of makes the Aid-granted hit points the opposite of 5e's temporary hit points, in that they're lost last.

In short, I don't trust my reading of the spell. Can anyone help explain it to me?

Answer 1

They go away. The spell gives you a loan of 5 current HP and 5 max HP, and when the spell ends, you give 5 max HP and 5 current HP back.

(Maybe they intended you to keep the current HP like in other healing spells, but I'd be hard put to reason that the "for the duration" somehow makes the maximum HP temporary, but not the current HP too. We've also little indication this was a mistake, other than it's surprising. So, let's go by what they wrote.)

That can drop you to 0hp, but by the end of the 8 hours, you're probably resting and in a healthy state, and the loss of a portion of your HP won't be devastating.

The fact it can drop you to 0hp might be surprising, but it makes sense from the spell's description:

Your spell bolsters your allies with toughness and resolve.

The spell gives you a little bit of extra oomph to keep you going. (Well, eight hours of oomph.) When the spell goes away, that oomph does too. If you're decently healthy, you'll feel slightly more worn. If you're at 1-4hp, basically on the brink of passing out and dying, then this oomph is the little bit extra that's still keeping you going, and it will be bad if it goes away.

Have healing spells handy if you have someone under Aid, and keep track of time to make sure they're in a healthy state when it ends.

Of course, if you find the above absurd or terrible or something else, you can feel free to say the 5hp granted goes away first, just like temporary HP.

Isn't it Temporary HP?

Probably not. D&D 5e does have rules for Temporary Hit Points, but this spell doesn't appear to grant them. They could have written "temporary HP", but instead they wrote "current HP".

The argument could be made they should be interpreted as Temporary HP because they're temporary, but nothing in either Aid's description nor the writing about Temporary HP really suggests this interpretation should be made. Aid seems to grant real HP, which means it can do things Temporary HP can't do, like bring you back from 0hp.

Answer 2

I asked Mike Mearls about this on Twitter:

Are the hit points from "Aid" supposed to be temporary hit points?

general rules for HP should cover that - your current hp cannot go above your max. if they are, they drop to your max immediately.

This sounds like it's somewhere in-between the answers we've got here. When Aid expires, your current hit points are adjusted down to your natural max, if they're higher than your max. Otherwise, they're yours to keep, I guess.

Answer 3

You lose the granted hit points again

Aid says

Each target's hit point maximum and current hit points increase by 5 for the duration.

But what does it mean to increase your current hp by 5 for the duration? Clearly it cannot mean that you now have 5 indestructible hp for the duration that nobody can remove. So what it must mean is that the spell grants you 5 additional hp when the duration starts, and then you lose 5 hp again, when it ends.

There is one possible complication when losing the hit points again: what happens if you have less than 5 hit points at that point in time?

The game rarely talks about the loss of hit points directly, but there are other examples, one is the Bearded Devil, wich has a Glaive attack that says:

If the target is a creature other than an undead or a construct, it must succeed on a DC 12 Constitution saving throw or lose 5 (1d10) hit points at the start of each of its turns due to an infernal wound.

The rules for Damage and Healing (p. 197, PH) say

A creature’s current hit points (usually just called hit points) can be any number from the creature’s hit point maximum down to 0. This number changes frequently as a creature takes damage or receives healing.
Whenever a creature takes damage, that damage is subtracted from its hit points. The loss of hit points has no effect on a creature’s capabilities until the creature drops to 0 hit points.

That is, no creature can fall below 0 hit points.

As you cannot be reduced to below 0 hit points, there are two possibilities if you lose more than your remaining hit points: either you lose your remaining hit points and there is no other consequence, or you treat the loss of hit points as damage, which might cause instant death if the spillover damage equals or exceeds your hit point maximum (p.197, PH):

Massive damage can kill you instantly. When damage reduces you to 0 hit points and there is damage remaining, you die if the remaining damage equals or exceeds your hit point maximum.

The rules say that damage causes loss of hit points, but does that mean that all loss of hit points is damage? Not strictly.

Since the rules really do not expand on it, it will be up to the DM if they treat loss of hit points as damage, or not.

If the DM decides to treat this as damage, death from massive damage could happen. One example is if the DM allows for death saves for NPCs, and the aid was cast on a commoner who only has 4 hp maximum, and has aid end with 1 remaining hit point.

If aid is upcast, the risk of death from massive damage increases. Say a friendly high-level cleric cast a 5th level aid spell on a fist level PC to grant them 20 added hits and hit point maximum. If that PC took more than their normal hit points in damage and then aid ended, then the PC would die from massive damage because the loss of 20 hits would be more damage than their hit point maximum.

Answer 4

Aid could use some help

Aid can't really work as written

Aid says:

Each target's hit point maximum and current hit points increase by 5 for the duration.

The hit point maximum increasing by 5 for the duration is easy to understand. The current hp increase not so much, because of the way hp work.

Most values or scores in the game have a permanent base number, which may then be modified by ongoing or continuous effects of specific durations. Calculating the score at any given point is simply a matter of determining which effects are currently in play. This is true for things like ability scores, speed, armor class, etc. For maximum hp, you know the character's base value, and at any given moment it might also be affected by the aid spell (duration 8 hours), draining from an undead (duration until the next long rest), and so forth.

But current hit points aren't like that. Current hp is not a base value to which ongoing continuous affects are applied. Rather, current hp are a running total and when something changes them, it changes them at once and permanently - you don't track the duration of the effect. When you take damage, you remove those hp immediately and they stay gone. When you heal, you add hp at that time and then they stay there. In fact, the Sage Advice Compendium emphasizes how healing is an instantaneous effect, not an effect with a duration that could be dispelled:

Another example: cure wounds instantaneously restores hit points to a creature. Because the spell’s duration is instantaneous, the restoration can’t be later dispelled. And you don’t suddenly lose hit points if you step into an antimagic field!

Thus, to say as aid does, that it increases the current hp 'for the duration' doesn't really make sense - that's not how current hp work. At the start of the duration adding them is easy enough - a target that receives the spell has their current hp increase by five. But suppose they later take damage - does that damage come off of the hp bestowed by aid, or the other ones, or some of each? Are the hp from aid the first ones to be lost or the last ones to be lost as a character takes damage? How could hp come off the ones bestowed by aid, if those hp are supposed last for the duration? If the hp from aid "go away" at the end of the duration, what if they have already been lost?

We can try to make sense of this by saying that aid is a continuous effect that provides a creature with 'five more current hp than they would otherwise have without the spell'. That seems reasonable enough, calculate current hp, with the all the instantaneous additions and subtractions that you normally would, and then at end of your calculations just add five. This 'add five at the end' can be run as a continuous effect that applies for the duration of the spell. This seems like it would work, until we realize the problem of zero.

Suppose a creature has 10 hp and receives aid. Calculate their hp as normal, then add five. They now have 15hp. Good.

Then they take 5 damage. Calculate their hp as normal (10-5 = 5), then add five. They are now at 10hp. Good.

Then they take 7 damage. Calculate their hp as normal (5-7 = 0, by the rules of hp, unconscious and making death saves), then add five. They are now at 5hp. Hmm.

If our rule is that aid is a continuous effect that adds 5 to current hp for 8 hours, a character with aid cannot drop below 5hp.¹

So, let's try this. Aid is not a continuous effect. Rather it 'loans' the target 5hp when cast, but 'takes them back' at the end of the duration. Does that work? Well, for one thing that's not how the spell is written, but if it works I'd be willing to forgive that. Unfortunately it doesn't work, either, largely because the 'taking them back' mechanism is not described. If a character was at 10 thanks to aid, at the end of the spell they drop down to 5, easy enough. But what if they are at 3? Even if the spell 'takes its hp back', it can only take back three - what happens to the other two still 'owed?' (another version of the problem of zero). If I am at 0hp but stable when the spell's duration runs out, I can't lose hp, but does the attempt to 'take them back' count as a source of damage? Do I have to start making death saves? Then again, if I am inventing some mechanism by which the spell removes current hp at the end of the duration, what happens if the spell doesn't reach the end of its duration? What if it is dispelled? Do I still have to pay the hp back? If I do, how could the spell take them back if it has been dispelled and is no longer in effect?

Aid cannot work as written because current hp is not a base value to which ongoing continuous affects are applied.

What can we do?

A better model for a version of aid that actually works is provided by the spell heroes' feast. This is an instantaneous spell that provides some immediate benefits (hp gain, cured of diseases and poison), as well as some ongoing effects that persist for 24 hours (immune to poison, being frightened, advantage on Wisdom saves, increase in max hp). Most relevant in that while it provides a continuous effect increase in maximum hp, for current hp it just says that hp are gained, without even calling them current hp.

This is what a functional version of aid would do; treat the change in current hp as a one-time, instantaneous gain, with nothing to be 'paid back' later, but retain the increase in max hp as an ongoing effect for the duration. Personally, I would keep aid as a spell with an 8 hour duration rather than make it an instantaneous spell with a lingering 8 hour effect, as befits a spell of second level that should be capable of being dispelled or suppressed by an anti-magic field (unlike the sixth level heroes' feast).

To answer the question, then, if aid is run in a way that makes sense, there is no change to a target's current hp when the spell ends - unless the drop in max hp requires the current hp to drop to the new, lower, maximum, as the already existing rules about max hp require.

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¹ This situation is analogous to that of a character being drained of strength by a shadow but wearing gauntlets of ogre power. On every hit, the character's base strength score is dropping, but they are also under a continuous effect from the gauntlets that resets their strength to 19. As another example, a character wearing a headband of intellect and then subject to the lair action of a Dyrrn. Even though they are being drained of intelligence, the headband is a continuous effect that resets their Int to 19. In a similar manner, no matter how many hp one loses, the continuous effect of an aid spell run as written means that one cannot drop below 5hp.

Answer 5

They lose current hp, but only if the ones from aid haven't already been lost

For the record, I think the aid spell can't be run as written. But if you are going to try, I suggest treating it like temporary hp. The hp from aid are not temporary hp, but they are like them.

Compare the wording of aid:

Your spell bolsters your allies with toughness and resolve. Choose up to three creatures within range. Each target's hit point maximum and current hit points increase by 5 for the duration.

with that of false life:

Bolstering yourself with a necromantic facsimile of life, you gain 1d4 + 4 temporary hit points for the duration.

They both "bolster" the target by increasing/gaining them hp "for the duration". The only significant difference is that aid applies to current hp and false life gives temporary hp. It would be reasonable to treat them similarly to one another (except for the differences that already exist between actual and temporary hit points).

When a creature takes damage, that damage comes off its temporary hp first. If it takes more damage than it has temporary hp, the difference is applied to its actual hp.

By analogy, when a creature bolstered by aid takes damage to its actual hp, that damage should be applied first to the aid-given hp. Only once it has taken more damage than the hp supplied by aid would its natural hp be affected.

When a creature that has temporary hp reaches the end of the duration of the temporary hp (or it completes a long rest), those temporary hp go away - but only if they haven't already been "depleted". That is, if I had 5 temp hp but lost 3 to damage, when my false life ran out, I would lose the 2 remaining temp hp, not all 5, despite all 5 existing "for the duration". The extra 3 hp already lost ("depleted") are not applied as 'damage' to my actual hp.

By analogy, when a creature bolstered by aid reaches the end of the duration of its granted hp, those granted hp go away - but only if they hadn't already been lost. That is, if I had 5 hp granted by aid but lost 3 to damage, when the aid ran out I would lose the 2 remaining hp, not all 5, despite all 5 existing "for the duration". The extra 3 hp already lost are not applied as 'damage' to my actual hp.

Run this way, you would need to track how much total damage the aided creature had taken since the application of the aid, but because the extra hp granted by aid are 'lost first', you would only have to total the damage until all the hp from the aid had been 'depleted' and then you could ignore them after that. Only if the creature had not taken as much damage during the duration as the hp they had been given would their current hp drop by the difference.