Do you know when you're going to retire, how much you'll have in income, or what you'll spend your money on? Chances are good that, even if you think you know the answers to these questions, you're probably not correct.

Americans have a lot of expectations about retirement, but a lot of those expectations don't pan out. In fact, here are three really big things Americans often get wrong about retirement.

Binder labeled retirement savings plan with a calculator on top of it

Image source: Getty Images.

1. The age at which they'll retire

Most Americans think they'll work well into their 60s. Most pre-retirees responding to a Nationwide survey said they'd work until 65, while almost four in 10 Americans responding to a Willis Towers Watson survey said they'd work into their 70s. 

The reality is, many Americans will be forced out of the workplace much earlier because of physical problems or an inability to find a job. Around 64% of workers said they've been victimized by age discrimination or seen it at work, and an analysis from Schwartz Center for Economic Policy Analysis revealed a real unemployment rate for those 55 or older at 2.5 times the national jobless rate. 

Statistics like these explain why 62 is the most popular age to claim retirement benefits, despite most Americans indicating they'll work much longer. 

If you're forced out of work early, this has a profound impact on your financial security. You'll begin drawing from savings sooner -- assuming you have any -- and could run out of money faster. You'll also have fewer years to save, and Social Security benefits will be reduced if you must claim them early. 

Unfortunately, there's no way to predict if you'll have to stop work before you're ready. The best thing to do is to invest as much as possible as early as possible to build a nest egg to support you if you're forced into early retirement. And, if health issues prompt you to leave the workforce early, look into Social Security Disability rather than just relying on savings.

2. How much they'll receive in Social Security income

Social Security is designed to replace only around 40% of pre-retirement income, while 53% of future retirees and 59% of recent retirees responding to Nationwide expect benefits to cover at least half of expenses.

Most people overestimate what Social Security will do for them because they think their benefits will be bigger than they are. Most future retirees expect they'll receive $1,578 in Social Security benefits, which is more than the average monthly benefits received by current retirees. 

Many people are way off when estimating benefits. According to the American Enterprise Institute, a third of near-retirees overestimated how much they'd receive from Social Security by 10%, while a quarter thought they'd receive 28% more than they'd get. And for one in 10 retirees, their actual benefit was half what they'd expected it would be. 

Overestimating how much you'll receive in Social Security creates unrealistic expectations. If you make this mistake when you're young, you may save too little. If you make this mistake when you're older, you may retire too early or fail to cut your cost of living. 

To find out how much your Social Security benefits are likely to be, visit mySocialSecurity. You'll see projected benefits at 62, full retirement age, and 70.

If you're young, set your retirement savings goals as if you'll receive the lowest benefit. If you're near retirement, adjust your budget based on the reality of how much your benefits will be. If you can't live comfortably, you'll need to work longer or take drastic steps to cut costs of living, such as moving to a cheaper area. 

3. How much they'll spend on healthcare

Future retirees responding to Nationwide indicated they expected to spend 20% of Social Security benefits on healthcare. This is a major underestimate, which retirees quickly discover. 

Around a quarter of retirees said healthcare costs are preventing them from having the retirement they expected. Among seniors with health problems, three-quarters said health issues arose sooner than anticipated, with most saying they experienced health issues at least five years before they'd expected to. 

Healthcare is a huge issue, with mean healthcare spending among those 65 and older coming in at close to $6,000 annually, according to the Bureau of Labor Statistics. Since the average monthly benefit for a 62-year-old retiree is just $1,076, according to the Social Security Administration, healthcare could take half of your Social Security check. 

And, if you have serious health problems, things could be even worse. A senior couple in the 90th percentile for prescription drug use needs around $370,000 to cover healthcare costs.

If you fail to plan for healthcare, you're likely going to be in serious financial trouble. Start saving for healthcare when you're as young as possible, ideally by investing in a health savings account if you're eligible. If you don't have access to a health savings account, consider increasing retirement savings goals to account for healthcare expenditures. 

Being realistic about retirement helps you avoid financial disaster 

The sad truth is, many Americans will be forced out of the workforce earlier than planned, will have lower benefits than expected, and will have higher healthcare costs. But this doesn't mean you have to give up hope.

You can plan for the reality of retirement when you're young by saving aggressively for retirement and can respond to the reality when you're older by taking steps to cut expenses, such as downsizing or moving to a cheaper area.

If you have a realistic view of retirement and adjust your actions accordingly, you can still achieve financial security and enjoy your life as a senior.

The Motley Fool has a disclosure policy.