From page 164 of the PHB (here is the equivalent section of the Basic Rules):
Spell Slots. You determine your available spell slots by adding together all your levels in the bard, cleric, druid, sorcerer, and wizard classes, half your levels (rounded down) in the paladin and ranger classes, and a third of your fighter or rogue levels (rounded down) if you have the Eldritch Knight or the Arcane Trickster feature. Use this total to determine your spell slots by consulting the Multiclass Spellcaster table.
If I have a level 3 ranger and multiclass into paladin, how are my available spell slots calculated?
- (ranger/2, rounded down) plus (paladin/2, rounded down)
- (ranger + paladin)/2, rounded down
Which one is it?
Best Answer
Your second way.
"... by adding together all your levels" would mean that your second example (ranger + paladin)/2 rounded down is how you'd work it. The rule doesn't have you segregate the levels before dividing if they are the same category. The example given in the book is a case of two different categories being combined, otherwise it would not have arrived at 5th level.
In your example, the result is 2 on the table, giving you 3 first level spells total for both this level and the next level you attain (be it 3/2 or 4/1).
The categories boil down to four the way the rules are presented:
Spell Caster (Druid, Cleric, Sorcerer, Wizard)
Half Caster (Paladin, Ranger)
Not quite a Half Caster (Eldritch Knight/Arcane Trickster)
Warlock (Pact Magic gets different treatment and is segregated)
*Note: (Thanks @Nick) As a practical matter, for both Ranger and Paladin, some DM's will rule that you would use the multiclassing spell rules once you are level 2 since both of those classes have their spellcasting feature come on line at 2d level. (See the tables and class description for each class). Ruling that once spellcasting is 'turned on' by one class it is always on will not break the game.