Its good to give factual numerical values. But I looked up GWWCs explanation for the suspiciously round number of 10% and it is:
Why 10%?
We chose 10% because it strikes a good balance. It is a significant proportion of one's income, in recognition of the importance of the problem and the need to take real action. But it is also within reach of most people in the developed world.
There is also a strong historical connection to the idea of tithing, a tradition in Judaism and Christianity of giving 10% of your income to charity or the Church. Islam has a similar practice (zakat) in which those who are able give between 2.5 and 20% to the poor and needy.
The pledge is of course just a minimum. Some members decide to go further than this and pledge to give a higher percentage, such as 20% or even 50%.
So this 10% appears to be arbitrary from the point of view of the OPs question. There seems to be no ethical reasoning behind the 10%. At least it looks more like charity-optimization. This may sound harsh, but this is what it looks in this light.
At least it looks more like charity-optimization. This may sound harsh, but this is what it looks in this light.
Could you explain what you mean by charity-optimization? I'm confused why you characterize labeling something as charity-optimization as sounding harsh.
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.