Do -1/-1 counters and +1/+1 counters cancel each other out?

Whenever a permanent has both +1/+1 counters and -1/-1 counters on it at the same time, the game automatically removes one of each as a state-based action. This keeps happening until only one type (or neither) remains. This process is defined in CR rule 704.5q.

State-based actions are checked continuously by the game — before any player gets priority — so the counters never truly coexist in a meaningful way. You cannot, for example, use the presence of both counter types to trigger abilities twice or exploit any interaction that requires both to be present simultaneously.

It is important to note this only applies to the same permanent. A +1/+1 counter on one creature and a -1/-1 counter on a different creature have no interaction whatsoever.

Example: You control a 2/2 creature with two +1/+1 counters (making it a 4/4). An opponent's spell places two -1/-1 counters on it. State-based actions immediately remove two +1/+1 counters and two -1/-1 counters — all four cancel out — leaving your creature back as a 2/2 with no counters.

This annihilation rule exists to keep the counter system clean and prevent permanent accumulation of opposing counters on a single card. It is referenced in the Comprehensive Rules under state-based actions at CR 704.5q.