[RPG] How do hit-dice work in Pathfinder


I'm absolutely new to Pathfinder and table-top RPGs, and I don't understand how are hit dice used after leveling. AFAIK, hit dice are used to calculate yout max HP when you start playing, but how do you use them when you get more of them?

Best Answer

Hit Dice determine the number of Hit Points of a character or a monster.

They are also used as an equivalent of Character Level in some case, for instance for spells that works differently depending of the power of the target.
For instance, the Adaro has 4d10+8 HP, i.e. 4 Hit Dices. If it is hit by a Color Spray (and fail the Will Save), it will only be blinded and stunned for 1d4 rounds, then stunned for 1 round. It would be the same for a level 4 Player Character.

Hit Points calculation for Player Characters

When your character starts, their Hit Points are the maximum of the hit dice of their class, plus their \$CON\$ bonus (minimum 1 after the \$CON\$ bonus, which is negative if the \$CON\$ is less than 10).
Each time they level up, they gain more Hit Points. To determine how much, this time you roll the dice of the class they take for this level and add the \$CON\$ bonus (minimum 1 after the \$CON\$ bonus).

Example: A Fighter with a \$CON\$ of 14 has the maximum of the Hit Dice of the class \$(\text{d}10) + CON\$ Bonus at the first level, so 10 + 2 = 12 HP.
He then takes another level in Fighter, and gains \$\text{d}10 + CON\$. Let's say he rolls 8. He gains 8 + 2 = 10 HP, for a total of 22 HP
For his third level, he decides to take a level as a Wizard (for the sake of demonstration :) ). This class' Hit Dice is a d6, so he gains \$\text{d}6 + CON\$. Let's say he rolls 2. He gains 2 + 2 = 4 HP, for a total of 26 HP

You also have to take into account the Favored Class Bonus, which can be either +1HP or +1 skill rank (or one of the racial variants, like those ones for the half-elves).

There are also alternative rules to rolling the hit dice, like taking half of the dice (rounded up or down), so a Barbarian player (Hit Dice d12) wouldn't be really annoyed because they rolled less than 3, four levels in a row.
I personally prefer “half the dice (keeping the 0.5*), rounded down if not integer” (so, for a Fighter (d10), the progression would be 10 at the first level, then (10 + 5.5 = 15.5, rounded down) -> 15 at the second level, then (15.5 + 5.5 = 21) -> 21 at the third level, and so on.

*: Since the possible values of a d10 are \$\left[1,2,3,4,5,6,7,8,9,10\right]\$, its "average" (Expected Value) is 5.5, not 5. The same goes for all "even" dices.