Your choice among actions has null altruistic value with respect to the consequences of the actions you choose among. Opportunity cost to others is not a valid consequence of an action when that cost derives from the absence of an alternative action. The consequences of your actions do not include the absence of all or any other actions that you could have done instead.
Only actions have an altruistic value to calculate. All the actions you considered and rejected in the past define a map of alternative worlds you never entered or alternative roads you never took. Your actions are the path you took through time. Only that path and the histories you can access on it can show you your consequences for other's well-being up to now. Your imagination of past alternative worlds might remind you of some altruistic value calculations of distance between altruistic values or what you do instead when you have an altruistic intention (for example, arguing with your conscience). None of that cognitive processing had any altruistic value to score or compare. All other things equal, when doing altruistic value calculations, your internal calculations and state are not your chosen actions while your external behaviors are your chosen actions.
You use information about consequences, intended or not, to decide altruistic value. That information does not help you establish the intent behind actions or the character of who chooses them. Furthermore, subjective evaluations used to rank, scale, or compare actions in terms of their consequences start with your beliefs about consequences. If you want to improve the validity of those beliefs (their fit to reality), altruistic value calculations won't help you. In fact, the only reason you are likely to use altruistic value calculations is to establish, for yourself, and according to yourself, the altruistic value of your actions.