Retirement planning is vitally important to financial security, but unfortunately millions of Americans are making serious mistakes in the process.

In fact, these four big errors most people make could come back to bite them when they're ready to leave the workforce.

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1. Failing to maximize Social Security benefits

Social Security is a vital source of retirement income, but most people don't know how to make the most of it. In fact, according to a study from Nationwide Insurance, just 8% of older adults can identify the factors that lead to the largest benefit.

Not understanding what affects the size of your benefit can be detrimental; claiming it early could reduce your standard benefit by as much as 30%, and lead you to miss an opportunity to earn delayed retirement credits.

To avoid this error, read how Social Security's benefit formula works and make an informed decision about the best age to start your benefits.

2. Counting on working in retirement

Around 55% of current workers anticipate they'll keep earning a paycheck well into retirement, according to data from the Transamerica Center for Retirement Studies. There's nothing inherently wrong with wanting to hold down a job late in life; the problem comes if you count on income from a paycheck and don't have it.

The reality is that very few seniors continue working in their later years. Often, that's because of a lack of opportunities or family or health issues.

So while you can aim to work as a senior, make your retirement plans based on the assumption this won't be possible. That means you'll need to save more, but doing so can protect you from a damaging financial shortfall if you have an unplanned early retirement.

3. Not setting specific planning goals

Only around 48% of Americans have tried to calculate the amount they'll need to save for retirement. That means the majority are flying blind when setting savings goals or determining if they're on track for a secure future.

You can't afford to save too little because you don't know how much money you need. To avoid this, pick a method of estimating your retirement savings goals and decide on your number. Break your big goal down into small ones, figuring out how much to save each year. You can follow your progress and change course if you fall behind.

4. Not planning for healthcare costs in retirement

Lastly, less than a third of Americans have tried to determine how much they'll need for healthcare costs as retirees.

Since healthcare can cost a senior couple with Medicare as much as $325,000 out of pocket over the course of retirement, it's easy to see why not planning for this expense could be a disaster.

To avoid this, read up on what care may cost as a senior and contribute money to a health savings account or a savings account earmarked for covering these expenses in your later years.

The $16,728 Social Security bonus most retirees completely overlook
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