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It takes years to build up your retirement accounts, but one simple mistake can undo all that hard work.

People often make costly mistakes without realizing it that can jeopardize their retirement and their future, and one financial planner says some are more common than others.

Here are the four biggest mistakes people make with retirement accounts that do the most damage.

1. Do not take advantage of a match with the employer

If you don’t get the full match in your 401 (k) that you’re eligible for, you’re running out of free money.

With a workplace’s 401 (k) program, any money you donate can equal a certain percentage of your salary.

Daniel Czulno, financial planner at Joule Financial and host of the DIY Money podcast, says correspondence is essential if available. “The calculations say it’s a 100% guaranteed return, and that’s the only place you can get it,” Czulno explains. “If you invest a dollar, they’ll give you a dollar equivalent, that’s pretty good. You can’t beat a 100% return.”

If it’s available to you, not taking advantage of that free money is a costly mistake.

2. Chase trendy investments instead of sticking to proven methods

Czulno says one of the costly mistakes he’s seen often is trying to keep up with investment trends.

“Especially this year we’re seeing a lot of people trying to figure out ‘How do I put bitcoin in my IRA?’ or that next meme stock, “he said.” But the math shows that over time, you can’t beat simple, low cost index investing. ”

Index funds collect a variety of stocks and bonds in each stock and generally have low fees. They are favorites of financial planners and even investment experts like Warren Buffett.

As an easy way to invest with lower fees than other stocks, index funds fight the complications and volatility of fashionable investing every day.

3. Make early withdrawals from a retirement account

Taking money out of a retirement account can be damaging in a number of ways and can mean you will have a lot less money to retire.

Czulno says there are two reasons for this. First of all, “You are beaten with income tax and penalties and so on,” he says.

The second reason is that you cannot always easily replace what you purchase due to the limits on account contributions. “We see people taking money out and not realizing that they are working against their maximum annual contribution,” he says. “They can never really replace the value they lost there.”

4. Forget 401 (k) s from previous jobs

Not riding your old 401 (k) for years might sound harmless, but it’s far from the truth.

Leaving an account in place for years means it might not be invested properly. “We see a lot of people getting ready to retire and not realizing that their 401 (k) from an employer from two decades ago is still aggressively invested and that they are approaching retirement.” , he said.

Typically, planners recommend investing less aggressively as you get older to minimize risk. “We find all these accounts and realize that [being] 100% invested in stocks has worked for them for a decade or two, but as retirement approaches it could be very costly. “

If your account is not renewed, it is much more difficult to manage this money and it could cost you dearly down the road. Fortunately, 401 (k) rollovers are pretty straightforward and involve a few steps to move all of your professional retirement accounts to another 401 (k) or IRA that you can manage.