How Multiclassing Works in D&D 5e

To multiclass you need a score of at least 13 in the primary ability of your current class and the new one. Every table has a player who wants a Fighter who casts, or a Cleric who sneaks. The SRD lets them do it, one level at a time. Here is the whole rule, quoted, then worked through on real characters so the trade is plain.

What multiclassing is

Multiclassing allows you to gain levels in multiple classes. 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.

You never lose a level. You choose where each new one goes.

The 13 rule

To qualify for a new class, you must have a score of at least 13 in the primary ability of the new class and your current classes.

Both ends count. A Barbarian going Druid needs Strength 13 and Wisdom 13. Here is each class's primary ability, from its Core Traits table:

"Or" means either one. "And" means both. A Monk going Paladin needs four scores at 13: Dexterity, Wisdom, Strength and Charisma.

How easy is 13? The Standard Array is "15, 14, 13, 12, 10, 8": three scores at 13 or more before your background adds its +2 and +1 (or +1 to three). Rolling 4d6 and dropping the lowest gives 13 or more 48.8% of the time per score. Across six rolls, that means at least two 13s 87.9% of the time, three 63.3%, four 32.1%. For more on the three methods, see Three Ways to Make Ability Scores.

Level counts: total or per class

Two things use your total character level:

The Experience Point cost to gain a level is based on your total character level, not your level in a particular class

Your Proficiency Bonus is based on your total character level, not your level in a particular class [...] if you are a level 3 Fighter / level 2 Rogue, you have the Proficiency Bonus of a level 5 character, which is +3.

Class features use your level in that class. A Fighter 3 / Rogue 2 has a Fighter's level 3 features and a Rogue's level 2 features, nothing higher.

Cantrips follow the total:

If a cantrip of yours increases in power at higher levels, the increase is based on your total character level, not your level in a particular class, unless the spell says otherwise.

Fire Bolt deals 1d10 and "increases by 1d10 when you reach levels 5 (2d10)". A Fighter 4 / Wizard 1 throws 2d10 Fire Bolts, the same as a Wizard 5.

Hit Points and Hit Dice

You gain the Hit Points from your new class as described for levels after 1. You gain the level 1 Hit Points for a class only when your total character level is 1.

The fixed values per level after 1 are 7 + Con for a Barbarian; 6 for a Fighter, Paladin or Ranger; 5 for a Bard, Cleric, Druid, Monk, Rogue or Warlock; 4 for a Sorcerer or Wizard. At level 1 a Fighter gets 10 + Con and a Wizard 6 + Con.

So the order matters. With Constitution +2:

Hit Dice stay as they came:

If these dice are the same die type, you can pool them together. [...] If you are a level 5 Cleric / level 5 Paladin, for example, you have five d8 Hit Dice and five d10 Hit Dice.

What you get from the second class

Not everything. Each class has an "As a Multiclass Character" box. A Fighter as your second class gives "Hit Point Die, proficiency with Martial weapons, and training with Light and Medium armor and Shields" and its level 1 features. A Rogue gives its Hit Point Die, one skill, Thieves' Tools and Light armor. A Wizard gives only its Hit Point Die and level 1 features.

No class adds saving throw proficiencies after the first. Your first class picks your saves for life. A Wizard who later takes Fighter never gains Constitution saves; a Fighter who later takes Wizard keeps them, and Constitution saves hold Concentration.

Three things that don't stack

Extra Attack.

If you gain the Extra Attack feature from more than one class, the features don't stack. You can't make more than two attacks with this feature unless you have a feature that says you can (such as the Fighter's Two Extra Attacks feature).

A Fighter 5 / Paladin 5 attacks twice, the same as either at level 5.

Armor Class.

If you have multiple ways to calculate your Armor Class, you can benefit from only one at a time.

A Monk/Barbarian picks one Unarmored Defense. For the numbers on each choice, see Armor Class, What Each Point Buys.

Spell slots combine, but on their own table.

Spell slots

You determine your available spell slots by adding together the following:

• All your levels in the Bard, Cleric, Druid, Sorcerer, and Wizard classes
• Half your levels (round up) in the Paladin and Ranger classes

Then you read that total off the Multiclass Spellcaster table. The SRD's own example:

if you are a level 4 Ranger / level 3 Sorcerer, you count as a level 5 character when determining your spell slots [...] you have four level 1 spell slots, three level 2 slots, and two level 3 slots. However, you can't prepare any level 3 spells, nor can you prepare any level 2 Ranger spells.

Those level 3 slots still work. You cast lower spells with them:

If a lower-level spell that you cast, like Burning Hands, has an enhanced effect when cast at a higher level, you can use the enhanced effect as normal.

Spells you prepare stay per class: "as if you were a single-classed member of that class", each cast with that class's ability. Warlocks run apart: Pact Magic slots and Spellcasting slots can cast each other's prepared spells, but they don't add together.

The trade, in numbers

A level 5 Fighter with a Rapier, Dexterity 16, +6 to hit, against a Goblin Warrior (AC 15). The other option is Fighter 4 / Rogue 1, attacking once with Sneak Attack (an ally stands next to the goblin). Both need 9 or more: 60% to hit, 5% to crit.

The dip costs 2.45 damage a turn until the Fighter reaches level 5 in Fighter, at total level 6. It buys Expertise in two skills, Thieves' Tools and a Rogue's skill. Whether that is worth it is a table question. The math only says what it costs.

The Wizard dip is cheaper in damage and dearer in time. A Fighter 4 / Wizard 1 gets 2d10 Fire Bolts, two level 1 slots, and Shield or Magic Missile, but waits a level for Extra Attack the same way and needs Intelligence 13.

Before you multiclass

1. Check both 13s, old class and new.
2. Pick your first class for its saves and level 1 Hit Points.
3. Count when your main class gets its big level (Extra Attack at 5, level 3 spells at 5) and how far the dip pushes it back.
4. For casters, add the levels and read the Multiclass Spellcaster table, not your class's own.

For a level 1 start, see A Hero in Ten Minutes. For slots and save DCs, see Spell Slots, Save DCs and Components.

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.