What is the greatest amount of temporary hit points you can have at once?

Question

Title says it all, what is the greatest amount of temporary hit points a character can have at one time? I think it's 45 from using Armor of Agathys with a 9th level spell slot, but is more possible?

Anything in RAW is acceptable except the following:

• Weird wishes
• Epic boons

Answers should only consider temporary hit points, not hit point mitigation methods such as polymorph, warding bond, arcane ward, etc. An ideal answer would provide the maximum one can attain by a single character's effort and the maximum attainable with the aid of others (if it's higher).

Answer 1

1030

Blackrazor (DMG, p. 216) will give you temp hp = to the max of any creature you kill. So in theory as high as you can find.

The Tarrasque (MM, p. 286) has the most potential hit points of any creature published so far, at 33d20+330¹.

In any case, the Tarrasque of 5th edition has a maximum natural hit point score of 990. In addition one can apply the 2nd level abjuration spell aid using a 9th level slot to further increase the maximum hit points of the Tarrasque by 40. This makes the absolute maximum for the Tarrasque's hit points (and thus the maximum temporary hit points you could gain at once via Blackrazor) 1030. Of course, you could gain more if a more powerful creature or hit-point boosting ability were to be included in the game, but this is the most in published material.

---

1. Unlike in all previous editions, it is totally possible to murderize the Tarrasque with Blackrazor, the Tarrasque of 5th edition lacking the signature immortality-through-regeneration-unless-killed-via-wish of previous incarnations. It also no longer gives you 1d4 +5 magic shields for killing it, so that might be part of it.

Answer 2

Maximum temporary hit points is 1810

TheFiddlerWins' answer missed some things even at the time it was released. Again we use Blackrazor's Devour Soul feature (DMG 216) but we will also use the Potion of Giant Size magic item from Storm King's Thunder (236).

Devour Soul.

[...]

When it devours a soul, Blackrazor grants you temporary hit points equal to the slain's creature's hit point maximum.

-

Potion of Giant Size

[...]

For [24 hours if you are Medium or smaller], ... your hit point maximum is doubled

Since Potion of Giant Size can only affect Medium or smaller creatures we use a creature who is not the Tarrasque (who is larger than Medium... much larger...)

• Ancient Gold Dragon

  • Base hit points equal to 28d20 + 252. [Max: 812]

• Manual of Bodily Health

  • Increase Constitution to 30 (+10) for +1 hit point per Hit Die or +28. [Max: 840]
• Level 10 aid spell¹
  • Increases Maximum HP by 45. [Max: 885]
• Heroes' feast spell
  • Increase Maximum HP by up to 20 [Max: 905]
• The dragon uses Change Shape becoming a Medium humanoid
  • For the metallic dragons' Change Shape features, hit points are retained.
• Potion of Giant Size
  • This doubles Maximum HP. [Max: 1810]

So simply finish off this dragon with Blackrazor and enjoy your 1810 Temporary Hit Points.

^1: This is possible because of the Book of Exalted Deeds which says (credit to Ruse in the comments for mentioning this and heroes' feast):

Enlightened Magic. Once you’ve read and studied the book, any spell slot you expend to cast a cleric or paladin spell counts as a spell slot of one level higher.

Details on how this allows for tenth level spells can be found in these questions:

• Does the Book of Exalted Deeds allow level 10 spell slots?
• Does a spell cast using a 10th-level spell slot count as a 10th-level spell?

Answer 3

Up to 240 temp HP

From Xanathar's spell Mass Polymorph (page 161)

Each target gains a number of temporary hit points equal to the hit points of its new form.

The Giant Ape has 15d12+60 HP, which could generate up to 240 HP depending on how you roll the hit die.

No aid from others, you can't Stack Temp HP

Others can't help, and you can't combine sources of temp HP (from the PHB, 198)

If you have temporary hit points and receive more of them, you decide whether to keep the ones you have or to gain the new ones.

Answer 4

You can go up to 200 with the eldritch invocation Tomb of Levistus:

You gain 10 temporary hit points per warlock level (XGtE 57)

Answer 5

Using Wild Soul (Unearthed Arcana, Barbarian and Monk) you can get a 10 when you enter Rage causing you to do 1d10 damage in a 30' radius, and you change the damage into temp HP, so you can theoretically get 11309.6 temp hit points because you can fit approx. 1130.96 tiny creatures in a 30' radius circle.

Wild Soul gives you the ability to do 1d10 damage to every creature around you.

Answer 6

If Unearthed Arcana is permissible, then as a Wild Soul Barbarian, it's possible to attain a theoretically infinite number of Temporary Hit Points

... Although in practice there's an upper limit constrained to what creatures the DM is willing to surround a Barbarian with.

On their Wild Surge table, a roll of [1] results in the following: "Necrotic energy bursts from you. Each creature within 30 feet of you takes 1d10 necrotic damage, and you gain temporary hit points equal to the sum of the necrotic damage dealt to the creatures." [Unearthed Arcana: Barbarian and Monk].

If we assume that all possible targeted creatures are medium size, crammed into a circle around the barbarian (as tightly as possible without creatures occupying the same space), and the barbarian rolls a natural [10] on the damage roll, they'd deal 10 Necrotic Damage to approximately 112 creatures (a circle of radius 30' has an area of 2,827 sq.ft, and each creature occupies a 5'x5' box, meaning ~113 creatures can be crammed into this circle, including the barbarian), gaining 1120 Temporary Hit Points. Give those creatures Vulnerability to Necrotic Damage, and they'd gain 2240 TempHP. If said creatures are tiny, It would be possible to cram approximately 451 creatures into this space, yielding (with vulnerability) 9020 TempHP. I leave it as an exercise to the reader to consider the scenario where these creatures are also airborne and spread out in the entire sphere surrounding the Barbarian, and not just the circle of space coplanar with the Barbarian on the ground.

I calculated about 144740 possible TempHP, hitting the maximum possible Tiny Creatures that all have Vulnerability―about 7237 creatures

Additionally, while there is a general rule that creatures cannot occupy the same space [Player's Handbook, pg. 191], there are some creatures not bound to this rule (notably Elementals), meaning it is indeed possible to cram an infinite number of creatures into the space surrounding the barbarian, therefore making it possible for said barbarian to hit an infinite number of creatures, and therefore gain infinite TempHP.

Answer 7

18080, by using the new UA Wild Soul barbarian subclass

You have to be at least a level 3 barbarian with the new Path of the Wild Soul subclass (from Unearthed Arcana: Barbarian and Monk). You must be surrounded in a speaker by 1808 enemies, then enter a Rage; roll a 1 on the d8 from the Wild Surge table, causing this result:

Necrotic energy bursts from you. Each creature within 30 feet of you takes 1d10 necrotic damage, and you gain temporary hit points equal to the sum of the necrotic damage dealt to the creatures.

And then you must roll a 10 on the d10 for damage. Thus, you get temp HP equal to 10 times 1808, for a total of 18080 temp HP.