Retirement is a phase of life it's better to plan for than dive right into. And many people do, indeed, spend the latter part of their careers planning for their senior years.

But there are a number of common retirement myths floating around that have the potential to upend your plans and make you miserable later in life. So in the course of your planning, do your best not to fall victim to these.

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1. Social Security will cover all of your senior expenses

Many people make a minimal effort to save for retirement because they're confident that Social Security will pick up the tab for all of their senior expenses. In reality, Social Security will only replace about 40% of your pre-retirement income if you're an average earner. And that assumes benefits aren't cut -- which we can't actually assume based on the state of Social Security's finances at present.

Many of the expenses that come into play during your working years are apt to monopolize your income in retirement as well. So all told, you should actually expect to need more like 70% to 80% of your former paycheck to live comfortably.

As such, retiring on Social Security alone won't cut it. Rather, you'll need savings of your own to ensure that you can cover your bills without worry.

2. You'll be all set with a $1 million nest egg

Maybe you are aware that retiring on Social Security alone is a bad idea, and you've been doing your best to sock money away in an IRA or 401(k) plan because of that. You may have your mind set on a $1 million savings goal. But getting hung up on that number might lead you astray.

It's true that $1 million is a lot of money. But it may not be enough to support your dream retirement.

On the flipside, you may not need $1 million in savings if you have modest goals for retirement, like downsizing your home and spending most of your time doing things locally. And in that case, why stress yourself to get to that $1 mark when you might do just fine on $500,000?

Rather than fixate on a single number, run your own numbers. Do your best to estimate your future expenses, and then land on a savings target that's likely to make it possible to live the lifestyle you want.

3. You'll enjoy every minute of being retired

Retirement can be a wonderfully liberating period of life. It can also get really boring really quickly.

You might think that once you no longer have a job to report to, everything will be peachy. But many retirees inevitably wind up missing work to some degree because at least it's something to get them out of the house.

That's why you may want to plan on some sort of part-time work in retirement. Having that structure could be a great way to avoid boredom and stay connected to other people. Plus, extra money never hurts.

It's a very good thing to plan for retirement rather than just wing it. But make sure not to buy into these myths along the way.