Most of us would agree that sharing our good fortune in the form of charitable giving is an ethical thing to do, maybe even an ethical requirement. If we’re blessed with more money than we need, whether by hard work, good luck, or a combination of both, we ought to lend a helping hand to those who need it. Right?

But what does it mean to have more money than we need?

The tax law passed in 2017 doubled the standard deduction, which means far fewer people get a tax break for their donations. As many warned, that led to a drop in individual contributions, but the drop was only 1.1 percent, according to Giving USA. That’s going in the wrong direction, but it is still less of a drop than feared. That’s good news, but it didn’t surprise me that much.

Charitable giving is a subject I often think about. As a volunteer tax preparer for the low-income and elderly, I’m frequently surprised by how many people who have little still give away a lot. The bulk of those donations tend to go to a church, and there may be complex reasons for the commitment, but I’m still impressed that people who have little voluntarily live on less.

Certainly there are plenty of wealthy people who donate a lot—people like Michael Bloomberg and Bill and Melinda Gates, to name a few—but a lot of relatively well-off people do not give much. Should that be a strictly personal decision? Or is turning a blind eye to the less fortunate an unethical act?

Princeton University Professor Peter Singer, in his lectures and books, especially The Life You Can Save, tries to understand not only why people give or don’t give, but also where they should give to have the most effect. The two questions are inseparable because some people don’t give because they’re not convinced it will help or because they can’t see it helping.

Singer often uses the classic example of the drowning child. Imagine you’re walking along and you see a young child struggling to stay afloat in a nearby swimming hole. You look around for parents or a babysitter but see no one, so you wade in and pull the child to safety. In the process, you’ve ruined a $200 suit and an $85 pair of shoes. But so what? You feel great for having saved a life. You’ll gladly fork over $285 to replace the damaged items.

But would you just as quickly and easily write a check for $285 and send it to feed starving children in a nation 5,000 miles away?

You may, but all the evidence indicates that we’re more likely to help when we have personal contact with the person in need. The farther away, the more abstract, the harder to see the results—all these things make charity a less likely outcome. Why do charities use the telephone to solicit help? Because even though we all hate those night-time calls, we’re more likely to say yes to a human being on the other end than we are to respond to a piece of mail.

Those of us in the United States and other developed countries are in a particularly strong position to help those most in need. According to the Organization for Economic Co-Operation and Development (OECD), about 2.5 billion people of us are “affluent” –defined as having money to spend on non-essential items. An equal number, according to the OECD, live in abject poverty, without adequate food, clean water, or protection from preventable diseases.

Singer notes that it wouldn’t take much of a sacrifice for those of us in the affluent category to cut our spending by $2.50 a day and donate that money to charity, and $2.50 is about what it takes to feed a family in many parts of the world. We might spend $2.50 a day on an expensive drink, for example, when we can just as easily drink tap water. Or we can go to ten movies a year instead of twelve, or eat out twenty times a year instead of twenty-five. None of these would be a huge sacrifice. Still, relatively few of us are willing to do it.

And even if we do, how do we get the $2.50 to the other side of the world in a way so that it really serves its intended needs? That turns out to be a lot harder than it sounds.

To help with this problem, several groups spend a lot of time studying charitable organizations. Charity Navigator is relatively well known for its work in ferreting out those groups that are efficiently run, with low overhead and minimal waste. But that doesn’t address the effectiveness of their programs. Give Well tries to do that, picking a couple of charities at a time and actually funneling money to them from donors. That gives Give Well more access to the inner workings of the charities they pick and more influence over how they are run.

That’s helpful and important. If we’re going to give, we want to make sure our money is going to really help. But it still leaves the question of whether and how much to give. Ultimately that’s a question of personal conscience, and yes, personal ethics.

How do you decide how much to give and to whom?