Retirement should be a time to enjoy life once you no longer have to go to work each day -- but it won't be if you don't make a plan for your financial security. Unfortunately, many people have some major misconceptions about retirement that affect their ability to make the right plans. 

To make sure you don't make a costly mistake that affects your future, here are four key facts about retirement you need to know that you probably weren't aware of. 

Senior couple with calculator and financial paperwork.

Image source: Getty Images.

1. There's no guarantee your spending will go down

Many financial experts recommend you save around 70% to 80% of pre-retirement income. In fact, there's even a rule called the 80% rule.

The problem is, not every retiree spends less after leaving the workforce. In fact, Employee Benefit Research Institute found almost half of all senior households actually exceeded pre-retirement spending in the two years after leaving the working world, and close to 33% exceeded pre-retirement spending a full six years later. 

Seniors who spent more than pre-retirement income didn't just exceed their income by a little bit. Almost 30% spent 120% more in their first two years of retirement than before leaving work, and close to a quarter were still spending 120% more six years later. 

If you base retirement savings goals on the premise that your spending will fall by a big margin after leaving work, you'll fall far short if you don't cut costs. Now that you know there's a good chance you'll spend more, aim to save enough to replace at least 100% of your pre-retirement salary if you can. 

2. More than half your Social Security check could go to healthcare

Speaking of extra spending during retirement, the big bucks you spend may not go toward globetrotting or spoiling grandkids. Instead, way more money than you expect will be spent on healthcare. 

Estimates vary, but most experts agree senior couples need substantial savings -- close to the mid six-figures -- to afford their essential care during retirement. And research from the insurance company Nationwide revealed seniors who claim Social Security at 62 may spend 64% of their entire Social Security check on medical expenditures. 

When substantial healthcare costs come as a surprise, financial disaster is the result. You don't want to forego necessary care or be forced to choose between food and medicine, so start socking away cash right now for healthcare. Use a health savings account (HSA) if you can, or put extra money into another tax-advantaged account that's earmarked for care costs. 

3. You'll probably retire earlier than expected

Around three out of four adults plan to work past retirement age -- at least part-time -- according to a recent Gallup poll. But among current retirees, the average reported retirement age was actually 61, which is way younger than the age when current retirees plan to leave the workforce. 

Why the disconnect? Likely because no one plans to be forced out of the workforce due to unemployment or illness -- but the Center for Retirement Research found health issues or involuntary unemployment were two major factors leading people to retire earlier than planned. 

If you can't work as long as you want, you'll have less time to save, and your savings will need to sustain you for longer. And if you don't have enough savings to live on, you may have to claim Social Security sooner than expected -- which will permanently reduce your benefits

Be prepared for the possibility of involuntary early retirement by saving more money when you're young and healthy. Set your retirement goals as if you'll have to leave the workforce at 62. If you're lucky enough to work longer, you'll have extra cash to enjoy life more. And you'll have the flexibility of choosing to retire when you're ready, rather than struggling to keep working out of financial necessity. 

4. Social Security won't provide enough to live on

Setting an appropriate retirement savings goal matters because Social Security benefits simply are not enough to provide a comfortable quality of life. Social Security is only designed to replace around 40% of pre-retirement income -- not the 100% or more you may need. Social Security benefits will barely keep you above the poverty level, and the buying power of benefits is eroding quickly because cost of living raises aren't large enough.

You must have money outside Social Security, and chances are it will need to come from savings. To make sure you've got what you need, put money into a 401(k), IRA, or other tax-advantaged savings account as soon as you're able. Invest as much as you can throughout your working years so you're ready when retirement arrives. 

Don't fall for retirement planning myths

Now you know some key facts about retirement that many Americans aren't aware of. It's up to you to use your newfound knowledge to adjust your plans for retirement savings so you can be a financially secure senior. It's worth making the effort so your golden years are a time of fun, not financial strife. Start today.