Figure out how much money you have to have so that the marginal dollar is that many times more valuable to them than to you. Donate everything beyond that.
This is probably not a bad idea for a heuristic, but reality is more complicated.
For instance, they don't share your values. You might not eat meat from animals who feel pain during the production, but they might. You might not circumcize babies without anaesthesia, but they might. You might not give money to harmful religious organizations, but they might.
You can factor all this is, but it is a lot more complicated than just figuring out how much marginal value a dollar would have for them. You have to figure out how much you value their having the marginal dollar, which requies modelling all the indirect consequences as well.
True, but my point was that you figure out at what point it's better to donate the marginal dollar, and you donate everything beyond that.
I'd like to hear from people about a process they use to decide how much to give to charity. Personally, I have very high income, and while we donate significant money in absolute terms, in relative terms the amount is <1% of our post-tax income. It seems to me that it's too little, but I have no moral intuition as to what the right amount is.
I have a good intuition on how to allocate the money, so that's not a problem.
Background: I have a wife and two kids, one with significant health issues (i.e. medical bills - possibly for life), most money we spend goes to private school tuition x 2, the above mentioned medical bills, mortgage, and miscellaneous life expenses. And we max out retirement savings.
If you have some sort of quantitative system where you figure out how much to spend on charity, please share. If you just use vague feelings, and you think there can be no reasonable quantitative system, please tell me that as well.
Update: as suggested in the comments, I'll make it more explicit: please also share how you determine how much to give.