Your proficiency bonus comes from your total character level: +2 at levels 1–4, +3 at 5–8, +4 at 9–12, +5 at 13–16 and +6 at 17–20. The 2014 and 2024 rules use the same table (SRD 5.1 "Character Advancement"; SRD 5.2 "Character Creation", Character Advancement table). A quick way to remember it: the bonus goes up by 1 at levels 5, 9, 13 and 17, or 2 + (level − 1) ÷ 4, rounded down.
Where you add it
You add the bonus once to any d20 roll that uses something you are proficient in:
- •Attack rolls with weapons you are proficient with, and every spell attack.
- •Saving throws your class makes you proficient in (two at level 1).
- •Ability checks with a proficient skill or tool.
- •Your spell save DC: 8 + proficiency bonus + spellcasting modifier. The spell save DC calculator does the full sum.
Expertise doubles the bonus for a chosen skill. Rogues get it at level 1 in both editions; bards get it at level 3 in 2014 and level 2 in 2024. It never stacks further: the rules say the bonus can be added or doubled only once per roll (SRD 5.1 "Proficiency Bonus"; SRD 5.2 Rules Glossary, "Expertise"). The same doubling flows into passive scores, so a level 5 rogue with Expertise in Perception and Wisdom 14 has a passive Perception of 10 + 2 + 6 = 18.
Multiclass characters
Proficiency bonus uses your total level, not your level in one class. A fighter 3 / rogue 2 is a level 5 character, so the bonus is +3 (the same example appears in both SRDs under "Multiclassing"). Plan a split with the multiclass calculator, and see when the next jump lands with the level progression calculator.
Monsters use Challenge Rating
A monster's proficiency bonus comes from its CR instead of a level: +2 up to CR 4, then +1 every four CRs up to +9 at CR 29–30 (Proficiency Bonus by Challenge Rating table, SRD 5.1 and 5.2). The 2024 stat blocks print it next to the CR, as in "CR 5 (XP 1,800; PB +3)". That number is already built into the monster's attack bonus, save DCs and skills.
Worked example
Bryn, a level 4 fighter with Strength 16 (+3), takes her fifth level. Her bonus rises from +2 to +3, so her longsword attack goes from +5 to +6, her Strength and Constitution saves each gain 1, and so does Athletics. Nothing about her ability scores changed. Fill the new numbers into the free character sheet.