Few people think of finance as an ethical career choice. Top undergraduates who want to “make a difference” are encouraged to forgo the allure of Wall Street and work in the charity sector. And many people in finance have a mid-career ethical crisis and switch to something fulfilling.

The intentions may be good, but is it really the best way to make a difference? I used to think so, but while researching ethical career choice, I concluded that it’s in fact better to earn a lot of money and donate a good chunk of it to the most cost-effective charities—a path that I call “earning to give.” Bill Gates, Warren Buffett and the others who have taken the 50% Giving Pledge are the best-known examples. But you don’t have to be a billionaire. By making as much money as we can and donating to the best causes, we can each save hundreds of lives.

There are three considerations behind this. First is the discrepancy in earnings between the different career paths. Annual salaries in banking or investment start at $80,000 and grow to over $500,000 if you do well. A lifetime salary of over $10 million is typical. Careers in nonprofits start at about $40,000, and don’t typically exceed $100,000, even for executive directors. Over a lifetime, a typical salary is only about $2.5 million. By entering finance and donating 50% of your lifetime earnings, you could pay for two nonprofit workers in your place—while still living on double what you would have if you’d chosen that route.

The second consideration is that “making a difference” requires doing something that wouldn’t have happened anyway. Suppose you come across a woman who’s had a heart attack. Luckily, someone trained in CPR is keeping her alive until the ambulance arrives. But you also know CPR. Should you push this other person out of the way and take over? The answer is obviously “no.” You wouldn’t be a hero; you wouldn’t have made a difference.

So it goes in the charity sector. The competition for not-for-profit jobs is fierce, and if someone else takes the job instead of you, he or she likely won’t be much worse at it than you would have been. So the difference you make by taking the job is only the difference between the good you would do, and the good that the other person would have done.

The competition for finance jobs is even more fierce than for nonprofits, but if someone else gets the finance job instead of you, he or she would not likely donate as much to charity. The average donation from an American household is less than 5% of income—a proportion that decreases the richer the household. So if you are determined to give a large share of your earnings to charity, the difference you make by taking that job is much greater.

The third and most important consideration is that charities vary tremendously in the amount of good they do with the money they receive. For example, it costs about $40,000 to train and provide a guide dog for one person, but it costs less than $25 to cure one person of sight-destroying trachoma. For the cost of improving the life of one person with blindness, you can cure 1,000 people of it.

This matters because if you decide to work in the charity sector, you’re rather limited. You can only change jobs so many times, and it’s unlikely that you can work for only the very best charities. In contrast, if you earn to give, you can donate anywhere, preferably to the most cost-effective charities, and change your donations as often as you like.

Not many people consider “earning to give” as a career path. But it’s proving popular. A good number of students that I’ve presented this idea to have pursued it. One student, convinced by these arguments, now works at Jane Street, the trading firm, giving 50% of his income, and thus can already pay the wages of several people for the not-for-profit work he could have been doing.

In general, the charitable sector is people-rich but money-poor. Adding another person to the labor pool just isn’t as valuable as providing more money so that more workers can be hired. You might feel less directly involved because you haven’t dedicated every hour of your day to charity, but you’ll have made a much bigger difference.

We welcome your comments at ideas@qz.com.

Now read the counter-argument: Don’t come to Wall Street for the money, even if you plan on giving it away