There is a lot of confusion regarding how to calculate the number of spell slots you get when you multiclass. This is my attempt at explaining it.

1. Dnd 5e Spell Slots Multiclass
2. 5e Multiclass Spell Slots Calculator

Spells Known and Prepared:
You determine what spells you know and can prepare for each class individually, as if you were a single-classed member of that class.

Gain access to spell slots of up to 5th level. (Arcane Trickster, Eldritch Knight) – Add 1/3 of class level total (rounded down) to the multiclass spellcaster level. Warlocks are special due to their Pact Magic class feature granting them the ability to use magic instead of the Spellcasting feature like other full casters. Abusing this ability will eat your 1st-level spell slots, so consider some levels in Sorcerer to get Font of Magic so that you can turn higher-level slots into cost-efficient 1st-level spell slots. Channel Divinity: Order’s Demand: If you have sufficient Wisdom to back this up, it can be effective both in and out of combat.

Spell Slots from the “Spellcasting” class feature:
• Add together all your levels in the bard, cleric, druid, sorcerer, and wizard classes;
• If you have one or more levels in the artificer class, add half these levels (rounded up);
• If you have two or more levels in the paladin class, add half these levels (rounded down);
• If you have two or more levels in the ranger class, add half these levels (rounded down);
• If you have three or more levels in the fighter (eldritch knight) class, add one third these levels (rounded down);
• If you have three or more levels in the rogue (arcane trickster) class, add one third these levels (rounded down);
Use this total to determine your spell slots by consulting the “Multiclass Spellcaster: Spell Slots Per Spell Level” table (PHB p. 165).

Note regarding Warlocks:
Warlocks do not have the “Spellcasting” class feature. Their spells come from the “Pact Magic” class feature. You track warlock spell slots separately from any class with the “spellcasting” class feature. However, you can cast any spell that is available for you to cast form any class using any spell slot of the appropriate level on your list of available warlock spell slots.

Dnd 5e Spell Slots Multiclass

Multiclassing in Dungeons and Dragons 5e can be rewarding, but it can also end up cheating you out of abilities you’d otherwise get — it mixes together aspects of various classes and does so in a way unique to this edition of the game. Multiclassing in previous editions worked differently per edition — the way it worked in AD&D or in 3rd Edition is not how it works now. So how does it work, and should you be looking at multiclassing? Well, to answer the second question first — the whole post is going to be about how it works — I’ll just say that there are significant pros and cons to multiclassing. Certain class combinations work extremely well together, and others really do not.

So let’s go over multiclassing, how it functions, and whether or not you should give it a try.

What is Multiclassing?

Multiclassing is, on the surface, very simple. You start off like all characters — your first level will be in a specific class. For the purposes of this example, we’ll say you started as a Wizard. Let’s say you made third level as a Wizard when you decided you wanted to focus on melee combat, and when you reached fourth level, you decided to multiclass as a Fighter. Great! Except in order to multiclass, you have to have a 13 or higher in the primary attribute for the class you’re currently playing (Wizard, in this case) and in the class you intend to pick up (Fighter). So if you only have a 12 Str, you can’t multiclass as a Fighter. These stats are called your prerequisites.

You can see on the chart above what the primary attributes are for each class. So, for example, it’s easier to multiclass into a class you already have a high primary attribute in — so if you wanted to take a level of Paladin on your Warlock, you probably at least have that Charisma at or above a 13, but the Strength could be harder to come by unless you did your research in advance.

If you’re planning to multiclass from the jump, it might be worth it to put a strong stat in something you normally wouldn’t. If your Wizard starts off with the standard array of 15, 14, 13, 12, 10 and 8, for example, and you’re planning to multiclass into Fighter later, you might want to put your 15 in Intelligence, your 14 in Constitution, and the 13 in Strength. That 14 in Con is because it’ll help with HP while you’re trying to get ready to switch classes — a reasonably high Con is good for every single class, that’s why it’s not considered a prerequisite for any class.

More doesn’t always mean… more

Now, certain things are pretty straightforward. Your Proficiency Bonus is always based on your character level, not your class level. So in the case of your Wizard/Fighter above, if you took three levels of Wizard before starting to take Fighter levels, and took two levels of Fighter, you’re a Wizard 3/Fighter 2, which makes you a 5th level character, and thus your Proficiency Bonus is a +3, just as it would have been for a 5th level Wizard or 5th level Fighter.

Okay, so what do you get, and what don’t you get when you multiclass? Well, for starters, you don’t get all the proficiencies. Each class has a certain amount of proficiencies like armor types, weapon types, and in the case of classes like Bards skills and musical instruments you learn by taking a level in the class, which you can find on pages 163 and 164 of the Player’s Handbook.

When you multiclass into a new class, you get the features of that class at that level except for some special circumstances. For example, if you already have Extra Attack (you’re a 5th level Barbarian who decides to multiclass into Fighter or Paladin, for example) then your Extra Attack from your Barbarian levels do not stack with Fighter or Paladin Extra Attack — if you’re a 10th level character with 5 Barbarian and 5 Fighter levels, you do not get another Extra Attack when you hit Fighter 5.

This is also the case for Channel Divinity — if you’re a Cleric who multiclasses into Paladin, you’ll get different types of Channel Divinity, but you only get extra uses of it when you gain a level in a class that specifically states it grants an extra use of Channel Divinity. Similarly, Barbarian and Monk Unarmored Defense (or any other kind of Unarmored Defense that might happen down the line if a new class with it is added) doesn’t stack, and in fact, you can’t even get another kind of Unarmored Defense if you already have it. So Barbarians who take levels in Monk don’t get to add their Dex, Con and Wisdom to their AC.

How spellcasting complicates multiclassing

Okay, you’re thinking — that’s a bit complicated, but I have a basic understanding.

Well, buckle up. We haven’t talked about what happens when you multiclass between two or more spellcasting classes. This is where it gets complicated. If you just have one spellcasting class — say, the Wizard/Fighter I mentioned above — then you may be thinking we’re good, I just have the one class that can cast spells, I just use the rules for that class and level. And you’d be right, unless you took (as an example) the Eldritch Knight subclass, which you did because you hate me.

I’m going to try and cover this now, but I won’t lie — you should definitely go look at page 163-164 in the PHB here. Basically, for this example, let’s assume you’re a 5th level Cleric/ 4th level Wizard. You are a 9th level caster, who can cast 4 Wizard Cantrips, 4 1st level spells, 3 2nd level spells, 3 3rd level spells, 3 4th level spells, and 1 5th level spell. However, as a 4th level Wizard, you only know up to 2nd level spells, and as a 5th level Cleric, you only know up to 3rd level spells. However, you can cast the spells you know using those spell slots, essentially casting a 3rd level Cleric spell at 5th level, for example. You still have to prepare your Wizard spells as normal, and your Cleric spells in the usual manner. You’ve sacrificed deeper knowledge of spells for a broader array including divine and arcane spells.

Multiclassing Pros and Cons

We’ve covered the basics, but I mentioned there were pros and cons to multiclassing. The pros are generally rooted in the flexibility it offers. If you want to be able to combine a Barbarian’s rage with a Champion Fighter’s ability to get a Critical Hit on a 19, for example, going Barbarian/Fighter multiclass has a lot of appeal. Why wouldn’t you do that? Why not give your Monk a Rogue’s ability to sneak attack?

5e Multiclass Spell Slots Calculator

Well, for starters, the deeper you get into a class, the more features of that class unlock. An 11th level Fighter gets a 2nd Extra Attack, which your Barbarian 3/Fighter 8 will not have and won’t get for three levels. Similarly, you won’t be getting the Barbarian’s extra rages, Brutal Critical ability, or Fast Movement — you’ve given up a lot of strength that Barbarians get at higher levels to play a hybrid character who gets to add Barbarian rage and the power of a Primal Path (but just the first ability) to the toolkit of a Fighter. You’ll get those Fighter abilities later than someone who just stuck with Fighter from the beginning, and you won’t ever get certain Fighter abilities at higher levels like that last Extra Attack that Fighters get at level 20.

Now, for most players, stuff at level 20 isn’t all that important — most campaigns don’t even reach level 20, and even if you did, the ability to use a Barbarian Rage while getting two uses of Action Surge is nothing to sneeze at. It really comes down to what you actually want to do with your character and how you imagine them, but it does have to be pointed out again, the complexities of a multiclassed spellcaster are not easily navigated for all players. But if you really want to roleplay a character who started out a raging Barbarian before learning how to sing and encourage her allies? Yeah, you can do that — just make sure your Barbarian has a Strength and Charisma above 13.

Multiclassing might not be for you, but it exists if you’re feeling adventurous or have a character concept that just won’t be constrained by one class. For more resources, the folks at Critical Role did a pretty solid video explaining it here, and there’s lots of stuff available at D&D Beyond to help out.