Ability Scores and Modifiers

ScoreModifier
1-5
2-3-4
4-5-3
6-7-2
8-9-1
10-11+0
12-13+1
14-15+2
16-17+3
18-19+4
20-21+5
22-23+6
24-25+7
26-27+8
28-29+9
30+10

To determine an ability modifier without consulting the table, subtract 10 from the ability score and then divide the total by 2 (round down).

Because ability modifiers affect almost every attack roll, ability check, and saving throw, ability modifiers come up in play more often than their associated scores.