Hit points, also known as HP or hp, are your life. If your hit points reach zero, you usually die. The only way of avoiding death in this case is to wear an amulet of life saving. If you are polymorphed at the time, you will return to your natural form, unless you are wearing an amulet of unchanging, in which case you will die. Also, some deaths, known as instadeaths, kill you regardless of your hit points at the time. Many of these, including stoning and brainlessness, will still kill you if you are polymorphed.
More hit points are automatically gained whenever the player gains a new experience level. How much depends on the race, role, and constitution of the character. Fighter classes, such as a barbarian, generally start the game with more hit points and receive more hit points at each new level than other classes, such as a tourist.
Hit points can also be gained with some potions. Quaffing a potion of healing or potion of extra healing if already at maximum hit points gives you one or two (or five, in case of a blessed potion of extra healing) more hit points. A Potion of full healing raises your maximum hit points by four, or eight if blessed.
Other ways to raise maximum hit points include "nurse dancing" (letting a nurse hit you wielding no weapon and wearing no armor), a favor ("You are surrounded by a golden glow.") from praying to your god at an altar, and beneficial effects from a incubus or succubus encounter.
If your maximum hit points are no more than 5*(2+XL) where XL is your experience level (i.e. HP <= 15 at level 1, 20 at level 2 and so on), then when you pray with very low hit points, your god will increase your maximum HP by a random amount as well as healing you. This is a handy trick to use in the early game, especially for weak characters.
Once you have seen one of these messages, you will not see another for 50 turns.
- You hear the howling of the CwnAnnwn...
- You have less than 1/10 of your total hit points left.
- You hear the wailing of the Banshee...
- You have only 1 hit point left.
- Valkyrie/Wizard/Elf, your life force is running out.
- You have less than 1/10 of your total hit points left, are a Valkyrie, Wizard, or Elf character, and have fewer than four intrinsics.
- Valkyrie/Wizard/Elf, all of your powers will be lost...
- You have less than 1/10 of your total hit points left, are a Valkyrie, Wizard, or Elf character, and have at least four intrinsics.
- Valkyrie/Wizard/Elf is about to die.
- You have only 1 hit point left and are a Valkyrie, Wizard, or Elf character.
Those Valkyrie/Wizard/Elf messages are references to the Gauntlet Atari game.
At least one other message relating to hit points does not observe the 50-move rule:
- You don't have enough stamina to move
- You are stressed or higher, have less than your maximum hit points, and have less than 5 hit points (if polymorphed) or less than 10 (if not polymorphed). This does not occur on the Plane of Air, nor if you are overloaded (if overloaded, "You collapse under your load" as you normally would).
Hit point regeneration
Under normal circumstances, you recover hit points naturally with the passage of time. 
If you are below level 10, you will regenerate one hit point every (42 / (level + 2)) + 1 turns (see chart).
If you are level 10 or above, you will regenerate every third turn. If your Constitution is 12 or lower, you get one hit point. Otherwise, you get d(Con) hitpoints up to a maximum of your level minus 9.
If you are polymorphed, you instead regenerate one hit point every 20 turns. 
If your encumbrance is Stressed or worse, you will only regenerate hit points on turns when you aren't moving.
If you have the regeneration ability, you will regenerate one hit point on any turn you did not do so above.
|10+||3||1 or d(Con)|
If a monster has a level of 0, their hp is simply 1d4.
|20||paper golem, straw golem|
|40||flesh golem, gold golem, leather golem|
|50||clay golem, wood golem|
|60||glass golem, stone golem|
- We want low HP, but a high mlevel so they can attack well
Their hp is 10d8
- Not in endgame
- hp = (monster level)d4 + 4 * (monster level)
- In endgame
- hp = 8 * (monster level)
Some other monsters have fixed hit points. Any monster with a level of 50-127 calculates its hp by
- hp = 2 * ((monster level) - 6)
Their actual level is then approximated by:
- level = hp / 4
Raising Monster Maximum Hit Points
Monsters (including pets) gain levels by raising their hit points. Thus advancing levels and increasing hit points are one and the same goal for them.
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- allmain.c, line 171 Normal HP regeneration
- allmain.c, line 166 HP regeneration while polymorphed
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