He came up with a graduated scale, which resembles progressive income tax rates. He suggests that those who earn $105,000 to $148,000 contribute 5 percent of their gross income each year. Individuals or families earning $148,001 to $383,000 would donate 5 percent of the first $148,000 and then 10 percent of the next $235,000. The sliding scale goes up progressively; at the top, those making more than $10,700,000 would give gradually greater percentages until they were donating a third of all income over $8.8 million. Professor Singer’s website has a calculator that will do the math for you.)

If the top 10 percent of American families followed these suggestions, donations would yield about $471 billion annually (in 2008, the year before the book was published). That money would go a long way to reducing global poverty, as calculated by a United Nations task force headed by Jeffrey D. Sachs, an economist and professor at Columbia University. Professor Sachs estimated how much it would cost each year, from 2005 through 2015, to reduce global poverty in a sustainable manner. In 2015, for instance, it would cost $230 billion to meet eight goals that include things like reducing by half the number of people who suffer from hunger and don’t have access to safe drinking water.

Giving What We Can, a nonprofit group inspired in part by Professor Singer’s work, asks its members to pledge to a universal standard of giving — 10 percent of gross income — across all income levels. The group, which was founded in 2009 by Toby Ord, an ethics researcher at Oxford University, has 389 members. “The 10 percent figure was reached with the view that it was an attainable level of giving for the majority of people in the developed world, whilst still being a large enough amount to have an impact on many people living in extreme poverty,” said Stephanie Crampin, a spokeswoman.

Those are worthy goals. But Professor Singer said he encouraged people to start giving, even at a relatively low level, and then increase the amount as it became possible, “topping your personal best.”

TO WHOM TO GIVE Whatever you ultimately decide to give, you want to be sure your charitable dollars are being deployed effectively. “How well you give is far more important than how much,” said Katherina M. Rosqueta, founding executive director of the Center for High Impact Philanthropy at the School of Social Policy & Practice at the University of Pennsylvania. “The same amount of money can do a little good or a lot of good.”

Evaluating charities can seem like a daunting task simply because there is so much information to peruse. In the past, charity evaluators often focused on whether or not it was spending too much on overhead and administration. But in recent years, philanthropy experts say the focus has shifted to a charity’s results. Even well-known organizations like Charity Navigator, which grants star ratings to charities, has said it is working to change its ratings to include more results-driven factors.

Professor Singer’s TheLifeYouCanSave.org, also lists 10 recommended charities. Many of the organizations he suggests — from programs to protect children from parasitic worms to another, called GiveDirectly, that puts cash directly into the hands of poor Kenyans — draws on the work of researchers that evaluate the various causes’ impact. They include Innovations for Poverty Action, Professor Karlan’s organization, as well as recommendations made by GiveWell, a group that uses evidence-based results to make just three top recommendations, a list it updated earlier this week.