The rule’s focus on how much of a raise could be spent, rather than how much should be saved, helps keep people from feeling deprived, Mr. Wendel said.

It also helps people commit in advance to set aside a certain proportion of their raise to ease the sting of not spending it all. “It doesn’t hurt as much to save a future raise,” he said.

Many employers, drawing on behavioral economics research, now include automatic annual increases in paycheck contributions — sometimes called “automatic escalation” — in their retirement savings plans. But the option to automatically save a certain amount of a raise is less common, Morningstar said. The Plan Sponsor Council of America, an industry group, said it did not yet track whether companies offered such a feature.

Rules of thumb can help simplify complex calculations for savers, Mr. Wendel said, but for a detailed analysis of your retirement finances, it may help to seek professional advice.

Here are some questions and answers about saving for retirement:

What if this rule of thumb for saving a portion of my raise is a stretch for me?

Other guidelines can be helpful, if less than ideal, Morningstar found. One is to “save your age,” as a percentage of the raise. If you’re 30, you should save 30 percent of the raise; if you’re 50, save half.

Alternatively, save at least 33 percent of your raise. If your take-home pay increased by $1,000, you should save at least $333.

These two options, however, work best for savers in their 20s, 30s and 40s and become less effective as people age. The “spend twice your years to retirement” rule works across all age groups, the report said, because it usually involves saving the most money. Still, it may be financially difficult for some people to put into action.