If it is on your creature, you can decide whether to add a counter before or after it damages you.
2004-10-04
Putting on a counter is optional. If you forget, you can't go back later even if it is something you usually do.
Enchant creature
At the beginning of your upkeep, you may put an infection counter on this Aura.
At the beginning of the upkeep of enchanted creature's controller, this Aura deals X damage to that player, where X is the number of infection counters on this Aura.
