First, from a Jewish perspective tse-da-ka is in addition to and not instead of other things in life. By analogy, if I go to a restaurant, there is an inherent understanding that I better have access not only to the price of the food, but also enough for taxes and a tip.
My sense is that much tse-da-ka is built in to our tax-funded "social support systems." As such, while the Biblical tithe (10%) is honorable, it is way too high for most people. I recommend that each individual or family define a "core amount." If you want my guidance on what that core should be, I would suggest something in the neighborhood of 5% with additional donations beyond the core amount if one is motivated or moved by the causes of a particular year. For example, if there was a major world catastrophe, a temple building campaign, etc., there may be reason to aim for a supplemental donation beyond the core.
At least half of the core amount should go to some combination of the Temple and the Federation. Of the remaining core amount, at least half should go to "Jewish charities" because if we Jews don't support them, nobody else will.
There are quality-of-life luxuries that we all want (the expression is "champagne taste on a beer bottle budget"), but those luxuries should be computed on a post-tse-da-ka, post tax basis.
Back when I still worked in hi-tech, I got a kick out of someone who complained to me that he never had enough money, but came into work every day carrying his $3.50 latte from Starbucks.
From Karen and me, best wishes for enjoying the remainder of the summer.
Joshua L. Segal