D&D Proficiency Bonus Calculator

What Is the Proficiency Bonus?

The proficiency bonus is a flat bonus added to any roll where your character has training or expertise. It starts at +2 at level 1 and increases every four levels, reaching +6 at level 17.

Formula

Proficiency Bonus = 2 + floor((Level − 1) ÷ 4)

So a level 1 character gets +2, a level 5 character gets +3, and a level 17 character gets +6.

What It Applies To

Your proficiency bonus is added to:

• Attack rolls with weapons or spells you are proficient with
• Saving throws your class grants proficiency in
• Ability checks (skills) you are proficient in
• Spell Save DC (8 + Proficiency Bonus + Spellcasting Modifier)

If you have Expertise (Rogues, Bards), you double your proficiency bonus for certain skills. You never add proficiency bonus twice to the same roll, just once, or doubled if you have Expertise.

Full Proficiency Bonus Table

Practical Example

A level 7 Fighter with a +3 STR modifier attacks with a longsword they are proficient with. Attack bonus = +3 (STR) + +3 (Proficiency, level 7) = +6 to hit.

Multiclassing: use total level, not class level

This is the rule people get wrong most often, and it always errs in the same direction. Your proficiency bonus comes from your total character level, added across every class. A Fighter 3 / Rogue 3 is a level 6 character with a +3 proficiency bonus, not two level 3 characters with +2 each. Hit dice, spell slots and class features all work off class level. Proficiency bonus does not. It is the one number that ignores the split entirely.

Why it stays so small

Coming from earlier editions, +2 to +6 across twenty levels looks stingy. It is deliberate, and the design term for it is bounded accuracy. Because the bonus grows so slowly, a d20 roll never stops mattering. A level 20 hero still has a real chance to miss a goblin, and a pack of goblins still poses some threat to that hero. Compare that to systems where attack bonuses climb into the twenties and low-level enemies become literally unable to connect. It also means the DM can throw any monster at any party and have the maths stay coherent, which is the practical payoff.

Monsters have one too

A monster’s proficiency bonus is derived from its Challenge Rating on the same ladder: CR 0 to 4 is +2, CR 5 to 8 is +3, CR 9 to 12 is +4, and so on in the same four-step pattern. That is where a monster’s saving throw bonuses and skill bonuses come from when you build one from scratch.