If you’re a small-time donor with a few thousand bucks to give back, odds are you may not spend that money as wisely as you think. That’s because donating well takes another kind of investment: time. At some point, the time it takes to learn about various causes and charities simply outweighs the amount you’re investing.

It gets worse. Small donations don’t really make that big of an impact unless they can be grouped together. With just a small donation, you may not be giving whatever group you like that much of an advantage.

While pursuing his PhD in statistical learning theory at the University of California, Berkeley, Paul Christiano was bothered by both these issues, but then he came across someone who had, at least theoretically, solved them. Carl Shulman–a researcher at the Future of Humanity Institute at Oxford University and advisor for the Open Philanthropy Project, which tracks and analyzes which charitable causes make the most cost-effective impact (the group is associated with Good Ventures and the charity evaluator GiveWell)–had recently come up with something he called a donor lottery.

The donor lottery works like this: Many small-time donors put their sums toward the collective pot of a donor-advised fund, a philanthropic vehicle that lets people get the tax benefits of giving to charity and then decide where they’ll give the money after the fact. The National Philanthropic Trust describes them much like a charitable savings account: You can deposit as much as you like whenever you want without a set time frame for when exactly you’ll use it.

The amount that each person donated, compared to the total pot, would represent his or her probability of winning. Everyone could be assured their money will go toward a good cause, while at the same time their combined winnings would be big enough to actually make a difference wherever they got directed. For the one winner, the size of that sum would justify researching and deciding where to donate.

Christiano liked that logic and already had his own donor-advised fund at Vanguard Charitable. So he decided to put Shulman’s theory into practice. In December, he started a pool. Eighteen friends contributed a total of $45,650. Rather than proportion each donation into tickets, Christiano, given his graduate work, made some more complex arrangements about assigning chances of winning to each donor and choosing a winner. Suffice it to say, on January 15, Timothy Telleen-Lawton took sole control of the pool of cash.

The responsibility of donating everyone’s money now falls to Telleen-Lawton, who works at GiveWell. He donated $5,050 for an 11% chance of winning and ended up with roughly 10 times that. Coincidentally, he recently took a sabbatical, which is good, because he has quite a research project ahead.