Rule 606.5 · Loyalty Abilities

If the total cost to activate a loyalty ability contains multiple costs to add or remove loyalty counters, those costs are combined into a single cost to add or remove loyalty counters, as appropriate.

Example: A player controls Carth the Lion, which says, in part, “Planeswalkers’ loyalty abilities you control cost an additional [+1] to activate. That player also controls a planeswalker with three loyalty counters. To activate one of that planeswalker’s abilities that normally costs [+1], they put two loyalty counters on it. To activate one of its abilities that normally costs [−4], they remove three loyalty counters from it.