How is the ability modifier calculated?

The modifier is the ability score minus 10, divided by 2, rounded down. A score of 16 gives a +3 modifier, 14 gives +2, 10 or 11 gives +0, and 8 gives -1. This is the core of every check in 5e.

How does proficiency bonus scale with level?

Proficiency bonus is +2 at levels 1 to 4, +3 at 5 to 8, +4 at 9 to 12, +5 at 13 to 16, and +6 at 17 to 20. The formula is 2 plus the level minus 1, divided by 4, rounded down.

Expertise doubles your proficiency bonus for a specific skill. Rogues and bards gain it. A proficient character with expertise in Stealth and a +3 proficiency bonus adds +6 from proficiency on top of the relevant ability modifier.

Which ability does each skill use?

Each skill keys off a fixed ability: Athletics uses Strength; Acrobatics, Sleight of Hand, and Stealth use Dexterity; Arcana, History, Investigation, Nature, and Religion use Intelligence; Animal Handling, Insight, Medicine, Perception, and Survival use Wisdom; and Deception, Intimidation, Performance, and Persuasion use Charisma.

Does this include feats or magic items?

No. It computes the base modifier from ability score, proficiency, and expertise only. Add bonuses from feats, magic items, fighting styles, or spells separately when filling out your sheet.

D&D Proficiency Bonus & Skill Check Calculator

Every skill check and saving throw in D&D 5e is built from three pieces: an ability modifier, your proficiency bonus if you are trained, and expertise if you have it. This calculator assembles the full table for your character so you can fill out a sheet in seconds.

How it works

The three building blocks combine per skill:

ability modifier   = floor((score − 10) / 2)
proficiency bonus  = 2 + floor((level − 1) / 4)
skill modifier     = ability modifier
                     + (proficient ? proficiency bonus : 0)
                     + (expertise ? proficiency bonus again : 0)
saving throw mod   = ability modifier + (proficient ? proficiency bonus : 0)

Expertise effectively doubles the proficiency bonus for that one skill. Saving throws use the same ability-plus-proficiency rule but never get expertise.

Example and notes

A level 5 rogue with a Dexterity of 16 has a +3 Dexterity modifier and a +3 proficiency bonus. Proficient in Stealth, the bonus is 3 + 3 = +6. With expertise in Stealth it becomes 3 + 3 + 3 = +9. Their Acrobatics, if only proficient, is +6, while an untrained Strength (Athletics) check uses just the Strength modifier. The tool computes all eighteen skills and six saves at once. Remember to add anything from feats, magic items, or spells on top of these base numbers.