Few retirement decisions are as critical, or as easy to get wrong, as when and how to take your Social Security benefits. The rules can be so convoluted that many people rely on what they’re told by Social Security employees, but that could prove to be an expensive mistake.

Certified financial planner Kate Gregory of Huntington Beach, California, uses sophisticated Social Security claiming software to recommend strategies that maximize clients’ lifetime benefits. Gregory advised one of her clients, a widow, to apply for her own small retirement benefit first so that her survivor benefit could grow, then switch to the larger benefit later. When the woman contacted Social Security, however, she was told she could get the survivor benefit only.

“That left her really flustered,” Gregory says.

The widow eventually was able to get the benefits she’s entitled to in the correct order, but Gregory and other financial planners worry about people who don’t get professional advice and who could be led astray.

“Most people are going to say, ‘Well, that’s what the government told me’ and let it drop. And that’s unfortunate,” says CFP Mary Beth Franklin, author of “Maximizing Social Security Retirement Benefits” and a contributing editor for Investment News.

High cost of mistakes

A lot of money is potentially at stake. The difference between the best claiming strategies and the worst could add up to $100,000 over the lifetime of a single person and $250,000 for married couples, says William Meyer, CEO of Social Security Solutions, a claiming strategies website.

Even seemingly small decisions can have outsize consequences. People who apply for benefits might be told they’re eligible for six months of back payments and that claiming the lump sum reduces their monthly benefits only slightly. Over time, though, that reduction adds up, especially when cost-of-living increases are factored in.

“The agents are saying, ‘Hey, your monthly income only goes down $50,’ or whatever it is,” Meyer says. “They don’t tell you, ‘Hey, over your lifetime, that could be a reduction of $20,000.’”

A 2016 study by the U.S. Government Accountability Office found applicants “were not consistently provided key information that people may need to make well-informed decisions.” A 2018 report from Social Security’s Office of the Inspector General estimated that 9,224 widows and widowers age 70 and older were underpaid by about $131.8 million because they weren’t properly informed of their options.

Education, not advice

Social Security employees aren’t supposed to give advice, just education, Franklin says. But she and other financial planners can relate many stories of people being encouraged to sign up early when waiting was a better strategy, or receiving bad information such as being told they weren’t eligible for certain benefits or that they couldn’t take actions that were in fact allowed.

William Reichenstein, Social Security Solutions’ head of research, was eligible for a since-discontinued strategy called a restricted application that allowed him to receive spousal benefits based on his wife’s earnings record while his own benefit was left to grow. The Social Security agent who processed the application ignored Reichenstein’s directive and signed him up for retirement benefits instead. Reichenstein was able to withdraw the incorrect application and get the spousal benefits, but mistakes are often irreversible. He advises applicants to be informed and to respond quickly if Social Security makes a mistake.

“Find out what you’re eligible for and make sure you get that,” Reichenstein says.

To be fair, many people have no idea how complicated the claiming decision can be and may not understand what they’re being told by Social Security representatives, Franklin says.

Social Security administers several different types of benefits including:

• Retirement benefits based on your own work record

• Spousal and survivor benefits based on the work record of a current or former spouse

• Child benefits for the minor children of people receiving Social Security

• Various kinds of disability benefits

Each benefit comes with its own regulations, and the best strategy may depend on your marital status, your longevity, your tax situation and many other factors.

Where to get information

People can educate themselves by visiting Social Security’s recently redesigned site and learning how the various benefits work, Franklin says. AARP has a free Social Security claiming calculator that allows people to model different strategies.

Or you can spend $20 to $40 and up to use paid software, such as Social Security Solutions or Maximize My Social Security, that allows you to model more complicated situations, including those involving a minor child or a pension from a job that didn’t pay into Social Security.

Consulting a financial planner who uses similar software also can be a smart move.

Franklin urges people to learn as much as they can before approaching Social Security, then keep a record of all interactions with the agency, including the names of representatives and their direct phone numbers, in case they need to appeal or correct a decision.

“I’m not here to bash Social Security representatives because most of them work very, very hard,” Franklin says. “But the rules are so complex.”

Liz Weston is a columnist at NerdWallet, a certified financial planner and author of “Your Credit Score.” Email: [email protected]. Twitter: @lizweston.