"Wishful thinking" could be one way to describe many Americans' expectations about retirement. When you consider the modest financial resources that most workers have accumulated and the longer lives we're all living, the math just doesn't add up to workers' expectations about when they can retire and what their standard of living in retirement will be.

For example, a recent survey of American workers by the Transamerica Center for Retirement Studies (TCRS) shows that almost two-thirds of American workers (62 percent) are confident they'll be able to fully retire from the workforce with a comfortable lifestyle. The same proportion also expects that their standard of living will stay the same or increase while in retirement. Yet when you read the reported statistics about their accumulated retirement savings, the most accurate reaction might be "fuggedaboutit!"

The TCRS survey estimates that workers' median retirement savings is $71,000. Only 30 percent report accumulating $250,000 or more in retirement savings. As a quick reality check, let's use the 4 percent rule to estimate the annual amount of income that savings can generate. The median savings of $71,000 could generate an annual retirement income of $2,840, and $250,000 can generate an annual income of $10,000 per year.

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When asked how much savings they would need for retirement, TCRS survey respondents reported a median amount of $500,000. Using the 4 percent rule, this amount would likely generate retirement income of $20,000 per year.

Of course, Social Security has to be added to these amounts, but there's a very good chance that Social Security, plus the retirement income generated by savings, won't match retirees' current standard of living.

How did workers arrive at their estimated retirement needs? The most prevalent answer was "guess," reported by almost half (46 percent) of the TCRS surveyed workers. Only about 16 percent reported methods that have a good chance of being accurate -- "used a retirement calculator," "amount given by a financial advisor" and "completed a worksheet."

When asked about their top source of information about retirement planning, the most prevalent answer (35 percent) was "friends and family." This doesn't inspire much confidence, unless their friends and family are trained financial planners.

The TCRS survey results are consistent with another recent survey of retirement plan participants conducted by JPMorgan Asset Management. Over half of its respondents are confident they'll be able to retire at their ideal age and that their savings will last throughout their lifetime. Yet most aren't confident that they know how much to save each year to meet their goals. Only about one-third (34 percent) know how much monthly income their savings will provide in retirement.

The reality is, most workers aren't on track to save enough money to retire at age 65 and maintain their current standard of living. They'll need to work longer, reduce their standard of living in retirement or do some combination of the two.

It's not easy for people to live comfortably for a few decades in retirement. It takes planning and preparation, including accurately calculating your retirement needs or working with an adviser, estimating a realistic retirement age and taking specific steps to be able to work longer.

My new book, "Retirement Game-Changers: Strategies for a Healthy, Financially Secure, and Fulfilling Long Life," describes a holistic plan that starts with taking an inventory of your financial resources, planning to balance working longer with a realistic standard of living and taking care of your health so you can continue working. In the 21st century, you'll need a robust plan to live a long, healthy retirement.