If you live in an expensive city like New York or San Francisco and have an average job–say, you’re an office manager rather than a tech mogul or an investment banker–you probably don’t feel particularly rich. The gap between the rich and the rest of us is the biggest it has been since the Great Depression.

But it’s easy to forget how rich you really are: If you make $52,000 a year, you’re richer than 99% of the people on the planet. With a salary of $28,000, you’re in the top 5%. And even if you’re below the poverty line of $11,000 a year, you’re still making more than 85% of the world.

A new book called Doing Good Better, out on July 28, uses the global income gap, along with a few other economic calculations, as the basis for something called the 100x multiplier. If you give a donation to some of the poorest people in the world, your money will go 100 times further than if you’d spent it on yourself. Even if you might have felt powerless in the face of the world’s biggest challenges, inequality actually puts you in a unique position to help. The book says:

It’s not often you have two options, one of which is one hundred times better than the other. Imagine a happy hour where you could either buy yourself a beer for five dollars or buy someone else a beer for five cents. If that were the case, we’d probably be pretty generous–next round’s on me! It’s like a 99-percent-off sale, or getting 10,000 percent extra free. It might be the most amazing deal you’ll see in your life.

Right now, out of the $358 billion that Americans donate every year, only 5% goes directly to other countries. But because our money is worth so much more in a place like Rwanda, the book argues that it would be better spent in nonprofits working overseas. It’s one of the tenets of effective altruism, a movement championed by moral philosopher Peter Singer that considers how donors can do the greatest good with the money they give.

Many people don’t even consider giving globally. “I think the most basic reason is the scale of extreme poverty and global inequality is unimaginable,” says the book’s author, William MacAskill, a 28-year-old philosophy professor at the University of Oxford.

“I think we just live in this very morally counterintuitive world. When we look at people who are poor living in the United States, living on $11,000, we think those people are really badly off. It’s just a really strange state of the world when those people are still the richest 15% of the world, when they’re still 20 times richer than the poorest billion people.”

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While it might seem more natural to give locally–the people we see struggling everyday trigger our empathy and many people want to help their own communities–MacAskill argues that it’s arbitrary to give to a local organization just because it happens to be in our neighborhood. “Everyone has an equal right to a good life,” he says. If it’s possible to literally save multiple lives with an annual donation, versus funding a small part of a program in the U.S., he believes we should choose to save lives.