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Chapter 2: Character Creation / Ability Scores

Ability Modifiers and Ability Checks

Source Starfinder Core Rulebook pg. 21
The right-hand column in Table 2–1 shows the ability modifier corresponding to each ability score. This modifier is applied to die rolls related to your abilities, such as skill checks, attacks, and more. Nearly every roll is affected by your abilities in some way, often with additional modifiers from other sources, but they generally involve your ability modifier rather than your actual ability score. When you determine your ability scores, make sure to note their respective ability modifiers on your character sheet. If a change to an ability score ever alters its modifier, be sure to adjust any statistics that rely on that modifier.

Sometimes, a situation or ability might require you to attempt something called an ability check. In such instances, instead of attempting a check involving both your abilities and other factors (such as skills or saving throws that reflect your training and expertise), you attempt a check using just 1d20 + your ability modifier. This represents you trying to use your raw, untrained talent for that particular ability, such as attempting a Strength check to kick down a door. See page 242 for more information.

In the rare instance that you need to determine ability modifiers beyond the numbers presented in the table, such as for extreme high-level play, ability modifiers can be determined by subtracting 10 from the ability score and dividing that result by 2, rounding down if the final result is a fraction. For example, an ability score of 41 would have an ability modifier of +15 (since 41 – 10 = 31 and 31 ÷ 2 = 15-1/2, which rounds down to 15).