Health regeneration

This page discusses how the player health regeneration mechanism works, and how equipment and buffs affect the regeneration rate.

If the player is not hit for some time, health starts regenerating until the player is hit, and the pace at which the player regenerates is dependent on:
 * 1) Player's maximum health: higher health means higher regeneration.
 * 2) Movement: if the player is standing still, the regeneration rate is 2.5× higher.
 * 3) Rest: if the player is lying on a bed or sitting on a chair, the regeneration rate is higher.
 * 4) Time since the last hit: the longer ago, the higher the regeneration rate; this has a cap of 60 seconds (1 in-game hour), after which the regeneration rate no longer rises.
 * 5) Buffs and debuffs: for a feel you can have a look at the detailed explanation below, but keep in mind that the numbers do not represent health regeneration directly; they are just factors (higher is better).

The time the player has to wait until regeneration starts is highly variable from roughly 1/10th of a second to 17 seconds (32 seconds on expert mode) and is again dependent on maximum life, movement, and buffs/debuffs.

Details
Health regeneration (HR) is determined by the following formula:

$$ \text{regeneration}_{\text{health}} = \frac{1}{2} * \left[ \left(		\underbrace{			\left( \frac{\text{health}_{\text{max}}}{400}*0.85+0.15 \right) * \text{time}		}_{\text{regen}}		+ \underbrace{ \text{buff} }_{\text{buffs}}	\right) * \underbrace{ \text{move} * \text{expert} }_{\text{special}} \right] $$

and gives the health per second the player regenerates.

The formula can be split in to 3 parts and a bit of rounding: All this is rounded to the nearest whole number and finally divided by 2 to get the regeneration per second.
 * 1) The $\text{regen}$  part consists of:
 * 2) * $\text{health}_\text{max}$ : maximum Health of the player.
 * 3) * $\text{time}$ : factor for the time that passed until the last hit. A detailed definition can be found in the detailed explanation.
 * 4) **The $\text{time}$ value starts at 0, and rises by 1 every 5 seconds for the first 30 seconds. After that, it rises by 1 every 10 seconds, to a maximum of 9. (0<=time<=9) That means this part is 0 for at the first 5 seconds, but reaches 6 after 30 seconds, and 9 after 60 seconds. This does not consider the Shiny Stone buff, which can raise the time value to a maximum of 38, and alters the algorithm in other ways (see below).
 * 5) The $\text{buffs}$  part:
 * 6) * $\text{buff}$ : modifiers from the buffs and debuffs. All "R+n" values from the Buff and Debuff section can be added here (the n-part). (There are some buffs which affect other parts of the algorithm; again, see below.) This is the easiest part as the buffs are just added to the regeneration.
 * 7) The $\text{special}$  part consists of:
 * 8) * $\text{move}$ : either 0.5 if the player is moving or 1.25 if the player is standing still.
 * 9) * $\text{expert}$ : 1, except if the player is in expert mode and doesn't have the well fed buff, in which case it is 0.5.

The player will regenerate HR per second, not considering the 2 buffs Shiny Stone and Rapid Healing. This means if the player has HR=0.5 they will regain 1 health per 2 seconds and if the player has HR=5 they will regain 5 health per second. (Technically, rather than 5 health per second, they will get 1 health every 12 ticks✅ of game time.)

Technical explanation
The player has these health regeneration stats:
 * Regeneration Time (RT): How long the character has been regenerating for. This normally increases +1 per tick, capped at 3600, and resets to zero when the character takes damage (stopping regeneration).
 * Regeneration Rate (R): Hit Points (HP) regenerated per tick (1 point of R is equal to 0.5 HP/s). This increases the longer the RT (the longer the player has been avoiding damage).
 * Regeneration Counter (RC): Increases by R per tick, becomes 120 or over, or -120 or less, it will be reduced or increased by 120, and player will gain or lose 1 health.

The Regeneration Rate (R) determines how fast the RC changes. R is normally 0 or positive, but could be negative if the player is inflicted with any life-draining debuffs, like Poisoned.

Calculation
The base Regeneration Rate (R) is mainly determined by the Regeneration Time (RT), player's max Health (mHP), and whether player is standing or moving.

First, The RT is converted to an Effective Regeneration Time (eRT).
 * If RT <= 1800, each 300 RT boosts eRT +1.
 * If RT > 1800, each 600 RT above 1800 boosts eRT +1.

Here is an illustration of the relationship between RT and eRT:

Then, the base Regeneration Rate Finally, it will be rounded to the nearest whole number.
 * If the player is standing still, R will be multiplied by 1.25.
 * If the player is moving, it will be multiplied by 0.5.

So, for a brief conclusion: the longer player not getting hurt, the higher maximum health player has, the higher for the natural health regeneration rate. Also, standing still gives a 2.5X healing bonus compared to moving. Using an item does not count as moving.

After all of the above, if the player is in Expert mode and does not have a Well Fed buff, R will be multiplied by 0.5.

Item and buff effects
R is also affected by other items and buffs.

Note: Despite drowning being similar to life-draining debuffs, it only resets the RT and does not affect the RC and R. It directly reduces Hit Points instead.

Buffs
These apply if the player doesn't have any life-draining debuffs:

Regen debuffs

 * Feral Bite debuff: Base R is multiplied x0.5.
 * Bleeding debuff: Keeps RT reset to 0, so base R remains at 0.

Life-draining debuffs
These cancel the R boosts above, reset RT to 0, and reduce R by these values: Note: If you are under the debuff of Burning or Suffocation, instead of losing 1 health when RC reaches -120, you'll always lose 5 health when RC reaches -600.
 * Poisoned: -4
 * On Fire!: -8
 * Venom, Cursed Inferno, Frostburn: -12
 * Burning: -60
 * Suffocation: -40.
 * Electrified: -8 (when standing still), or -32 (when moving).
 * The Tongue: -100 only in Expert mode.

Honey

 * Which means Honey reduces the rate of any life-draining debuff.
 * Honey additionally boosts RT +2 per tick (RT increase is 3× as fast).

Shiny Stone
If the player is using items or not standing still, it will reset the multipliers of the Feral Bite debuff and Expert mode to 0.75 from 0.5. Both of them only reduce the regeneration speed by 25% instead of the previous 50%. It will also multiply base R ×1.1.

If the player is not using any items and almost standing still (it allows small amounts of movement), the following effects are applied in addition to those above:
 * 1) If the player has any life-draining debuffs so that R is less than 0, R is reduced by half (if you also have Honey buff, then it increases R by 4 first(but no more than 0), then, R is reduced by half, finally, the Honey buff additionally increase R by 2.).
 * 2) R +4.
 * 3) RT +4 per tick.
 * 4) If 90 < RT < 1800, RT is reset to 1800.
 * 5) When RT > 3000, it will remove the RT cap, and every 300 RT above 3000 will boost eRT +1 (this part is capped at 30, so it will give an eRT maxed at 38 instead of the previous 9).
 * 6) Finally, if R > 0, RC is boosted +1 per tick.

So, if the player is at 600 max HP, with the Shiny Stone and standing still, in Expert mode, without Well Fed:
 * RC is additionally boosted +1 per tick
 * = 32 Hit Points per second regeneration rate.
 * = 32 Hit Points per second regeneration rate.

A more complex example
To illustrate how items, buffs and debuffs interact with each other, here is a more complex example:

Assume the player has the Venom, On Fire! debuffs, the Regeneration and Honey buffs, has the Shiny Stone and Charm of Myths equipped, is standing next to a Heart Lantern, and is standing still.

According to the above, here is how life regeneration can be determined:
 * 1) The Regeneration buff and Charm of Myths increase R by 4 and 1 respectively, so, R = 5.
 * 2) The life-draining debuffs cancel out the effect above and set R to 0.
 * 3) The Venom and On Fire! debuffs reduce R by 12 and 8 respectively, so, R = -20.
 * 4) Because R < 0, the Honey buff increases R by 4, so, R = -16.
 * 5) As R is still less than 0, the Shiny Stone cuts it in half, so, R = -8.
 * 6) Then the Honey buff, Shiny Stone, and Heart Lantern increase R by 2, 4, and 2 respectively, so, R = 0.
 * 7) Because the player has life-draining debuffs, RT will remain at 0, so player will not have natural health regeneration.
 * 8) As R is not greater than 0, the Shiny Stone will not provide the RC +1 per tick bonus.

Thus, the player has R = 0, and will neither gain nor lose any health.

But, if the player places a Campfire nearby, it will give R +1 boost and give the player a 0.5 HP/s regeneration rate. In addition, because R > 0, the Shiny Stone will now provide a RC +1 per tick bonus, granting an additional 0.5 HP/s regeneration rate. Thus, the player will now have a 1 HP/s regeneration rate.

However, if the player has the Rapid Healing buff (which gives the RC +6 per tick effect and does not affect R) instead of placing a Campfire, the Shiny Stone will not provide the RC +1 per tick bonus. So instead, the player will have a 3 HP/s regeneration rate.