About this tool
The D&D 5e Ability Modifier & Point-Buy Calculator does the three bits of arithmetic every character sheet needs. Enter your six ability scores (Strength, Dexterity, Constitution, Intelligence, Wisdom and Charisma) and a character level, and it returns each ability's modifier, the proficiency bonus for that level, and the total cost of the array under the standard point-buy system. Everything runs in your browser with plain integer math — no dice, no server.
The modifier for any score is floor((score − 10) / 2), so a 15 is +2, a 10 is +0 and an 8 is −1. Proficiency bonus scales with level as 2 + floor((level − 1) / 4): +2 at levels 1–4, +3 at 5–8, +4 at 9–12, +5 at 13–16 and +6 at 17–20. Point-buy uses the official Player's Handbook cost table for scores 8 through 15 — 8=0, 9=1, 10=2, 11=3, 12=4, 13=5, 14=7, 15=9 — summed across all six abilities against a 27-point budget.
The tool flags whether the array is exactly 27 points, under budget, or over, so you can tune a legal spread before adding racial or ASI bonuses (apply those after point-buy, since a bought score never exceeds 15). If any score falls outside the 8–15 buy range the point-buy cost is shown as not applicable, because those scores cannot be bought — but their modifiers and the proficiency bonus are still calculated.