Altruistic behavior can be defined as behavior that benefits another organism, not closely related, while being apparently detrimental to the organism performing the behaviour, benefit and detriment being defined in terms of contribution to inclusive fitness.
Well, if you count opportunity costs as detrimental, something that benefits both you and me but doesn’t benefit you as much as something else you could do with your time and resources is still altruistic.
If it benefits you, it isn’t altruism—at least by the conventional biological definition of altruism.
Here is Trivers (1971) in “The Evolution of Reciprocal Altruism” on the topic:
Well, if you count opportunity costs as detrimental, something that benefits both you and me but doesn’t benefit you as much as something else you could do with your time and resources is still altruistic.
Traditionally, you compare with a “null” action—not the best thing you could possibly be doing.