How Proficiency Bonus Works in 5e
Every character starts at +2 and ends at +6. That one number, the Proficiency Bonus, sits under every skill, save, attack and spell DC you are trained in. Three features bend it: Expertise doubles it, Jack of All Trades halves it onto skills you lack, and Reliable Talent removes the low half of the die. Here is each, quoted from the SRD, with the odds.
What the bonus is
The SRD says it plainly:
All creatures have a Proficiency Bonus, which reflects the impact that training has on the creature's capabilities.
And where it goes:
This bonus is applied to a D20 Test when the creature has proficiency in a skill, in a saving throw, or with an item that the creature uses to make the D20 Test. The bonus is also used for spell attacks and for calculating the DC of saving throws for spells.
It grows with level for characters and with Challenge Rating for monsters, on the same table:
| Level or CR | Bonus |
|---|---|
| Up to 4 | +2 |
| 5–8 | +3 |
| 9–12 | +4 |
| 13–16 | +5 |
| 17–20 | +6 |
Monsters keep going past 20, up to +9 at CR 29–30.
It never stacks
Your Proficiency Bonus can't be added to a die roll or another number more than once.
The SRD's example: a check that allows Deception or Persuasion gets the bonus once, even if you are proficient in both. Two features that each say "add your Proficiency Bonus" still add it once.
Expertise doubles it
When you make an ability check with a skill proficiency in which you have Expertise, your Proficiency Bonus is doubled for that check unless the bonus is doubled by another feature.
Two limits sit in the same entry: Expertise needs a skill you are already proficient in, and "You can't have Expertise in the same skill proficiency more than once." The core rules add one more: "Whenever the bonus is used, it can be multiplied only once and divided only once."
Three classes get it in the SRD:
- Rogue: two skills at level 1, "Sleight of Hand and Stealth are recommended", two more at level 6.
- Bard: two skills at level 2, "Performance and Persuasion are recommended", two more at level 9.
- Ranger: one skill at level 2 (Deft Explorer), two more at level 9.
The Skilled feat gives proficiency, not Expertise.
What doubling buys
Take a Rogue with Dexterity 16 at level 1 (+3), 18 by level 7 (+4), 20 by level 11 (+5). Here are the odds of a Stealth check at each Difficulty Class. Ability checks have no automatic success on a 20, so a total that can't reach the DC fails every time.
| Rogue Stealth | DC 10 | DC 15 | DC 20 | DC 25 |
|---|---|---|---|---|
| L1, proficient (+5) | 80% | 55% | 30% | 5% |
| L1, Expertise (+7) | 90% | 65% | 40% | 15% |
| L7, Expertise (+10) | 100% | 80% | 55% | 30% |
| L7, + Reliable Talent | 100% | 100% | 100% | 30% |
| L17, + Reliable Talent (+17) | 100% | 100% | 100% | 100% |
At level 1, Expertise is worth +2, or 10 percentage points at every DC. By level 17 it is worth +6, the same as the whole bonus again.
Expertise also lifts passive scores. The SRD's formula is "Passive Perception = 10 + Wisdom (Perception) check modifier", and it says to "Include all modifiers that apply". A level 9 Ranger with Wisdom 16 and Expertise in Perception has a Passive Perception of 21 (10 + 3 + 8), against 17 with proficiency alone.
Reliable Talent removes the bad rolls
The Rogue's level 7 feature:
Whenever you make an ability check that uses one of your skill or tool proficiencies, you can treat a d20 roll of 9 or lower as a 10.
Nine of twenty faces become a 10, so your worst total is 10 plus your modifier. With +10 at level 7, the Rogue's floor is 20: every DC 20 Stealth check succeeds before the die lands. At level 17, with +17, the floor is 27, and DC 25 is certain too.
It works on any proficient skill or tool, not only the ones with Expertise. A level 17 Rogue with Strength 10 and proficiency in Athletics (+6) never totals below 16.
Jack of All Trades fills the gaps
The Bard's level 2 feature:
You can add half your Proficiency Bonus (round down) to any ability check you make that uses a skill proficiency you lack and that doesn't otherwise use your Proficiency Bonus.
Half of +2 or +3 rounds down to +1. It reaches +2 at level 9 and +3 at level 17. Small, but it touches every skill the Bard lacks. A level 9 Bard with Strength 10 makes a DC 15 Athletics check 40% of the time instead of 30%.
The feature names "a skill proficiency you lack", so it applies to skill checks. A plain ability check with no skill, such as Initiative, falls outside that wording. It never meets Expertise either: one needs the skill, the other needs you to lack it.
How to use this at the table
- Put Expertise where the party leans on you most. A Rogue scout uses Stealth every session; a Bard face uses Persuasion.
- Before rolling, check the floor. A Rogue with Reliable Talent who already beats the DC on a 10 can skip the roll.
- Write passive scores with Expertise included. A GM who asks for Passive Perception wants the full number.
The Book of Dice covers the d20 in Part I, The Object, and the odds of hitting a target number in Part III, The Rolling.
This work includes material from the System Reference Document 5.2.1 ("SRD 5.2.1") by Wizards of the Coast LLC, available at dndbeyond.com/srd. The SRD 5.2.1 is licensed under the Creative Commons Attribution 4.0 International License.
