Characters have a Proficiency Bonus (PB) determined by level, as detailed below. Monsters also have this bonus, which is incorporated in their stat blocks. The bonus is used in the rules on ability checks, saving throws, and attack rolls.

Your PB can’t be added to a single die roll or other number more than once. For example, if two different rules say you can add your PB to a Wisdom saving throw, you nevertheless add the bonus only once when you make the save.

Occasionally, your PB might be multiplied or divided (doubled or halved, for example) before you apply it. For example, the Rogue’s Expertise feature doubles the PB for certain ability checks. If a circumstance suggests that your PB applies more than once to the same roll, you still add it only once and multiply or divide it only once.

By the same token, abilities that don't benefit from your PB can not benefit from a feature or effect that allows you to multiply it. For instance, if you lack proficiency in the History skill, you gain no benefit from a feature that lets you double your proficiency bonus when you make Intelligence (History) checks.

In general, you don’t multiply your PB for attack rolls or saving throws. If a feature or effect allows you to do so, these same rules apply.

Your Proficiency Bonus starts at 2 at 1st level. This number increases to 3 at 5th level, 4 at 9th level, 5 at 13th level, and 6 at 17th level.

There are two types of Difficulty Classes (DCs) that are used by every character. Mastery Save DC and Spell Save DC

Every class either has one or both of these DCs used when determining whether a creature will succeed or fail resisting an effect that is being considered. Unless otherwise specified these DCs are calculated as follows:

Mastery Save DC = 8 + Proficiency Bonus + Strength or Dexterity modifier (you choose when acquiring the feature that gives you masteries)

Spell Save DC = 8 + Proficiency Bonus + Spellcasting ability modifier (your class will specify)

|                                                             Spell Slots per Spell level                                                            |

lvl    -     1st     -     2nd     -     3rd     -     4th     -     5th     -     6th     -     7th     -     8th     -     9th    -

1st    -      3      -                -               -               -                -               -               -               -             -

2nd   -      4      -                -               -               -                -               -               -               -              -

3rd    -      4      -       2       -               -               -                -               -               -               -             -

4th    -      4      -       3       -               -               -                -               -               -               -              -

5th    -      4      -       3       -       2      -               -                -               -               -               -              -

6th    -      4      -       3       -       3      -               -                -               -               -               -              -

7th    -      4      -       3       -       3      -       1      -                -               -               -               -              -

8th    -      4      -       3       -       3      -       2      -                -               -               -               -              -

9th    -      4      -       3       -       3      -       3      -       1       -               -               -               -              -

10th  -      4      -       3       -       3      -       3      -       2       -               -               -               -              -

11th  -      4      -       3       -       3      -       3      -       2       -      1       -               -               -              -

12th  -      4      -       3       -       3      -       3      -       2       -      1       -               -               -              -

13th  -      4      -       3       -       3      -       3      -       2       -      1       -      1       -               -              -

14th  -      4      -       3       -       3      -       3      -       2       -      1       -      1       -               -              -

15th  -      4      -       3       -       3      -       3      -       2       -      1       -      1       -      1       -              -

16th  -      4      -       3       -       3      -       3      -       2       -      1       -      1       -      1       -              -

17th  -      4      -       3       -       3      -       3      -       2       -      1       -      1       -      1       -      1      -

18th  -      4      -       3       -       3      -       3      -       3       -      1       -      1       -      1       -      1      -

19th  -      4      -       3       -       3      -       3      -       3       -      2       -      1       -      1       -      1      -

20th  -      4      -       3       -       3      -       3      -       3       -      2       -      2       -      1       -      1      -

Multiclassing allows you to gain levels in multiple classes. Doing so lets you mix the abilities of those classes to realize a character concept that might not be reflected in one of the standard class options.

With this rule, you have the option of gaining a level in a new class whenever you advance in level, instead of gaining a level in your current class. Your levels in all your classes are added together to determine your character level. For example, if you have three levels in wizard and two in fighter, you’re a 5th-level character.

As you advance in levels, you might primarily remain a member of your original class with just a few levels in another class, or you might change course entirely, never looking back at the class you left behind. You might even start progressing in a third or fourth class. Compared to a single-class character of the same level, you’ll sacrifice some focus in exchange for versatility.

You gain the hit points from your new class as described for "levels after 1st". You gain the 1st-level hit points for a class only when you are a 1st-level character.

You add together the Hit Dice granted by all your classes to form your pool of Hit Dice, ensuring to keep track of different hit die sizes. For example, if you are a paladin 5/cleric 5, you have five d10 Hit Dice and five d8 Hit Dice.

Your Proficiency Bonus is calculated using your character level, rather than any of your classes' individual levels.

When you gain your first level in a class other than your initial class, you gain only some of new class’s starting proficiencies, as shown in the Multiclassing Proficiencies table below.

A few class features have additional rules tied to them when multiclassing as specified below.

Channel Divinity

If you already have the Channel Divinity feature and gain a level in a class that also grants the feature, you gain the Channel Divinity effects granted by that class, but getting the feature again doesn’t give you an additional use of it. You gain additional uses only when you reach a class level that explicitly grants them to you. For example, if you are a Cleric 6/Paladin 4, you can use Channel Divinity twice between rests because you are high enough level in the cleric class to have more uses. Whenever you use the feature, you can choose any of the Channel Divinity effects available to you from your two classes.

Extra Action

If you gain an extra action from more than one of your classes, you gain an extra Bonus Action instead of an Action for each additional granting of the feature from a new class. If one or more of your extra actions have different limitations, you can choose which to use each time you use it, (such as Bladesinging Wizard's Martial Acceleration allowing the additional action after using a cantrip. Or an Artificer’s Magical Harmonization allowing multiple Magic Actions.)

Weapon Masteries

If you have a feature from multiple of your classes that allow you to Master weapons, you instead choose one class as your base, and gain one more Mastered Weapon than you would have before on the chosen class for each extra class that allows you to Master a weapon. You follow the chosen class’s rules on Mastered Weapons. If one of your classes is Rogue and you don’t choose it as your base, the extra weapon has one less mastery. If one of your classes is Barbarian, You must choose it as your base.

Spellcasting

Spells Known. Your known and prepared spells for each class are considered separately.

Spell Slot Calculation. If multiple of your classes have the Spellcasting or Sorcery feature, you add their levels together to calculate your Caster Level. "Caster" classes add their full level, "Half Caster" classes add half of their level (rounded down), and subclasses from "Martial" classes that give spellcasting add one third of their level (rounded down) to this calculation. You gain the spell slots of a Caster class of your Caster level. 

Sorcery Points. If you have both the Spellcasting feature and the Sorcery feature from the Sorcerer class, when calculating your Caster Level, add all classes together as normal and consult the Caster Spell Slot Table for your spell slots. 

To determine Sorcery Points, calculate your Sorcerer levels first. Gain Sorcery Points as you would normally for the number of levels you have in Sorcerer, removing the equivalent number of spell slots from the total gained for your Caster Level. Then you gain the remaining Spell Slots listed for your Caster level as Spell Slots. You can only use these sorcery points to cast spells of 5th level or lower that you know, and you can use them to cast spells from any of your classes. 

For example, a Bard 4/Sorcerer 3 would take your first 3 Caster levels and convert them to Sorcery Points (four 1st-level & two 2nd-level slots into 14 points), then gain the slots of your remaining Caster levels (one 2nd-level, two 3rd-level, and one 4th-level slot) 

Cross-Casting. You may use spellcasting resources from the Natural Magic, Pact Magic, Sorcery, and Spellcasting features to cast spells freely between any of your classes.