5e Ability Modifier Calculator

How Ability Modifiers Work in D&D 5e

Every ability score in D&D 5e has a corresponding modifier that's the number you actually add to dice rolls. The modifier is calculated using the formula: (score − 10) ÷ 2, rounded down.

The modifier is what matters mechanically. When you make an attack roll, you add your Strength modifier (not your Strength score). When you make a Dexterity saving throw, you add your DEX modifier. Spell save DC = 8 + proficiency bonus + spellcasting modifier. In almost every mechanical calculation, the modifier is the operative number.

This is why even-numbered scores are more efficient than odd-numbered ones: going from 15 to 16 (modifier +3) is a genuine improvement. Going from 16 to 17 doesn't change the modifier — you still have +3. That means 1 point buy point spent to go from 16 to 17 does nothing until you spend another point to reach 18.

Why Even Numbers Matter for Point Buy

In point buy, each score costs a different number of points to reach. Critically, the modifier only increases at even scores (10, 12, 14, 16, 18, 20). Odd scores (11, 13, 15, 17, 19) have the same modifier as the even score below them.

This creates an efficiency rule: always end on even numbers after racial bonuses. If your racial bonus is +2, buy a 14 base (not 13 or 15) to end at 16. If your racial bonus is +1, buy a 13 or 15 base (ending at 14 or 16). Buying 15 base + 0 racial = 15 modifier (+2), while 14 base + 2 racial = 16 modifier (+3) — the racial bonus makes all the difference.