Introduction
Most tabletop RPGs involve some amount of math, and Pathfinder 2e is no exception. Many players jokingly refer to Pathfinder as “Mathfinder”, and in some ways that nickname is justified.
But don’t worry, there’s nothing here that you can’t handle. The absolute most complicated math is very simply addition, subtraction, and either multiplying or dividing by 2. If you’re nervous or just don’t have a head for numbers, there’s no shame in using a calculator while you play.
Table of Contents
Modifiers, Bonuses, and Penalties
You will frequently add modifiers, bonuses, and/or penalties to rolls. These numbers are added to the total of the dice rolled. For example: you add your “attack bonus” to an “attack roll”, adding the bonus to the d20 roll for the attack. Similarly, you add a “damage bonus” to a “damage roll”, so a character attacking with a greatsword would usually roll 2d6 (the damage for a greatsword) and add a damage bonus to the total rolled.
A bonus is always positive, a penalty is always negative, and a modifier can be either.
In Pathfinder 2e, there are five types of modifiers: ability, proficiency, circumstances, item, and status.
Ability modifiers come from the Creature’s game statistics. Nearly any check will apply an ability modifier.
Proficiency is determined by a creature’s game statistics, and is never negative. A creature’s Proficiency bonus only changes if the creature’s game statistics change. For example: Joe has a +3 proficiency bonus in the Intimidation skill, and that won’t change until Joe gains a level.
Circumstance bonuses come from the circumstances under which a roll is being made. Sometimes things like class features or the circumstances of a situation can give creatures a Circumstance bonus.
Item modifiers come from equipment. Magic weapons provide item bonuses to attack rolls, armor provides an item bonus to AC and to saving throws, and tools can provide item bonuses to skill checks.
Status modifiers come from effects like spells and other magical effects.
When rolling a check, you can add all five bonuses (remember that bonuses of the same type don’t stack) to your d20 roll.
Penalties can be circumstance, item, or status penalties, but they can also be untyped. Penalties always stack, even if they’re of the same type.
Stacking
“Stacking” is the concept of combining numerical values from different sources.
Bonuses and Penalties
Bonuses of the same type do not stack; you instead use the highest bonus of that type.
For example: Joe attempts an Acrobatics checks to walk across a right rope. Joe has a +1 Dexterity modifier, +3 Proficiency Bonus in Acrobatics, and a +1 Item Bonus from a pole he’s using to balance. He has a +1 circumstance bonus from an ally aiding him and a +1 circumstance bonus from an environmental effect. These two Circumstance bonuses don’t stack, but Joe adds up their bonuses and gets a total bonus of +6 to add to their check (+1 ability modifier, +3 proficiency, +1 item, +1 circumstance).
Stacking Multipliers
Multipliers stack “additively”, which means that you add their effects rather than multiplying multiple times. For example: If you have two things which double a number, you instead triple the number. Each “double” adds the original value to the total one time, so doubling twice adds the original value to the total twice, resulting in three times the original value.
Rounding
When dividing numbers, always round down unless a piece of text specifically says otherwise. For example: Joe succeeds on a basic reflex save to avoid the damage from a fireball, which means that they they only take half as much damage as the fireball would normally deal. If the fireball deals 25 fire damage, they divide it in half and round down, resulting in Susan taking just 12 damage.
