I think there are two important facts to keep in perspective here.<p>First, polls have shown that U.S. citizens drastically overestimate the amount of the federal budget allocated to foreign aid. As I recall, the average estimate is 25%; the reality is less than 0.1%.<p>The comparison holds mainly not because Bill Gates is so rich, or because the U.S. is indebted, but because federal budget priorities drastically favor items that are not foreign aid. Those priorities are formed in part because citizens believe that the budget is already giving away huge quantities of money, making proposals to increase foreign aid unpopular.<p>Second, the amount of money spent is not necessarily a good measure of the amount of aid given. On the one hand, sometimes more money doesn't help; to use an analogy that people here might understand, after a certain point in increasing your budget for paying software developers, you are limited by your ability to find good people, not by your ability to pay them. Likewise, some foreign aid projects - such as HIV eradication in certain African nations - have reached the point where the amount of monetary aid given already exceeds the capacity of local infrastructure to use the resources wisely, and any more would just sit in a bank account somewhere until someone blew it on a useless boondoggle.<p>On the other hand, some forms of aid or assistance given by the U.S. to friends or allies do not have monetary value, such as military assistance, diplomatic cover, or political advice... and there are material goods that are, for whatever reason, more valuable to the people who receive them than the items would be priced in the U.S. market where they were paid for.<p>So although this is a true and revealing fact, it's best to not misinterpret it. The reasons for the foreign aid budget being lower than Bill Gates's charity contributions are political, not fiscal; but it's likely that the more important question about foreign aid is the nature and quality of the aid, not the U.S. dollar value for which it was purchased.