Multiclassing into a spellcasting class gives you the ability to cast spells of that class, but it doesn’t automatically grant you additional spell slots. Instead, you calculate your total number of spell slots by adding together all your individual class’s spellcasting levels.
For example, if you’re a 3rd-level wizard and a 2nd-level fighter, you have four 1st-level spell slots and two 2nd-level spell slots.
If you have multiple classes that grant you spellcasting levels, you calculate your total number of spell slots by adding together the levels from all your classes. For example, if you’re a 3rd-level wizard and a 2nd-level fighter, you have four 1st-level spell slots and two 2nd-level spell slots.
You can use any combination of your available spell slots to cast your spells. For example, if you want to cast a 1st-level spell and a 2nd-level spell, you can use one of your 2nd-level slots and two of your 1st-level slots.
Or you could use two of your 1st-level slots and one of your 2nd-level slots.
Once you use a given slot, it is expended until you finish a long rest, at which point all your expended spell slots are renewed.
The multiclass rules forspellcasting are actually quite simple: just add together the levels from all your classes that grantSpellcasting to determine the spells per day and spells known as if you were a single classed character of that level. The only “catch” is that each class’s contribution is halved for working out spells per day (and hence number of spells known) if it is not your primary class – i.e.
the one with the highest level – for working out caster level.