D&D Ability Score Modifier Calculator

Character sheet almost done, six scores written down, and then comes the part that stalls the table: turning each ability score into the modifier that feeds every check, attack roll and spell save DC. If you started playing last week you have not memorized the table yet, and a one point mistake only shows up later, when a roll misses by exactly one. Type the score and the modifier comes out signed, ready to copy.

The math is floor((score - 10) / 2), and floor is the word that matters: it always rounds down, negative side included. That is why 9 gives -1 instead of 0, 7 gives -2 and 1 gives -5. Anyone building a spreadsheet with truncation or ordinary rounding gets the top half of the table right and the whole bottom half wrong. Each modifier covers two consecutive scores: 14 and 15 give +2, 16 and 17 give +3.

The label suggests 1 to 30, the range the rules use, but the field blocks nothing: 50 returns +20, and a value with a decimal runs through the same formula instead of being rejected. Add racial bonuses, magic items or ability score improvements to the number before typing, since the page knows nothing about your sheet and only does the conversion. Proficiency bonus is separate math, added later. Everything runs in your browser.