Multiclass spell slots

Notes

Once you have the Spellcasting feature from two or more classes, you add up one spellcasting level: every level of Bard, Cleric, Druid, Sorcerer and Wizard, plus half your Paladin and Ranger levels, rounded up. That number on the multiclass table gives your slots.

The example in the rules: a level 4 Ranger / level 3 Sorcerer counts as level 5 (3 + half of 4), so four level 1 slots, three level 2 and two level 3. You still prepare spells per class as if single-classed, so you can end up with slots higher than anything you can prepare. They still work for lower-level spells, cast at the higher level.

Only one class with Spellcasting? Then the multiclass table doesn't apply; use that class's own table. The calculator says so.

Warlock levels don't count here. Pact Magic is its own thing, and those slots come back on a Short or Long Rest.

Paladin and Ranger together: the rules say halve and round up, but not whether to round each class separately or after adding them. I round each one on its own. If that's off by one for you, ask your DM how they read it.