The typical workplace 401(k) plan offers limited investment choices. If you're an avid investor, you may prefer more flexibility in what you can invest in.

A self-directed 401(k) plan may be just what you need. It offers something known as a "brokerage window," through which your employer may allow you to invest part or all of your 401(k) plan as you see fit. Your employer decides whether to offer this feature, as well as the types of investments you can choose from.

Self-directed 401(k) plans follow the same rules and requirements as other 401(k) plans. If your employer allows self-directed 401(k) plans, make sure you know these Internal Revenue Service rules before you make account contributions.

Calculator, cash, and magnifying glass highlighting the words 401(k) Plan

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1. Annual contribution limits

The limit on your elective deferrals -- the maximum amount you can have deducted from your taxable income and placed in your 401(k) account -- is $19,500 for 2020. The limit is increased regularly for inflation. If you're age 50 or older at the end of the year, you can make additional elective deferrals of up to $6,500 in 2020. Your employer can also make additional contributions for you, up to a maximum contribution in 2020 of $57,000 for those under age 50 and $63,500 for those 50 and over.

If you work for only one company during the year, you shouldn't have to worry about going over the limit for your 401(k) plan contributions -- your employer calculates this limit for you. If you work for more than one company, however, it's easy to go over the limit, as one employer doesn't know how much another already let you contribute.

If your elective deferrals for the year are over the limits, it's your responsibility to notify your plan administrator and have the excess contribution returned to you before the tax deadline for the following year. Otherwise the excess contribution does not reduce your taxable income and you must pay tax on it when you withdraw it. That means the same income is taxed twice. Leaving excess deferrals in your account can also cause the IRS to disqualify your plan.

2. Disqualified investments

If you have a self-directed 401(k) plan through your employer, don't take the "self-directed" part too literally. Your employer can still limit the types of investments you make. Some employers may limit you to mutual funds, for example.

You also won't get away with investing in anything for which you may receive an immediate benefit. You can't, for example, use your 401(k) to buy your personal home. And forget using your 401(k) to buy collectible automobiles, art, or vacation properties that you expect to use. You can't pay yourself to manage your own 401(k) plan investments, either.

If your employer allows it, however, you can invest in securities, investment real estate, gold, currency, and other investments.

3. Transactions between related parties

Don't entangle your 401(k) plan with your family members, either. For this purpose, "family members" are your parents, grandparents, children, grandchildren, or spouse's children or grandchildren.

That means you can't lend your 401(k) money to any of these relatives, let them live in property owned by your 401(k) plan, invest that money in your relatives' businesses, or otherwise cause your family members to benefit from your 401(k) investments.

4. Distributions

The rules for taking distributions from a self-directed 401(k) plan are the same as those for any other 401(k) plan. If you take an early withdrawal before age 59 1/2, you may have to pay a 10% penalty to the IRS in addition to ordinary income tax, unless you meet an exception.

Your employer's 401(k) plan may allow for hardship withdrawals when you have immediate and serious financial needs. In 2020, you can also take penalty-free withdrawals of up to $100,000 if your distribution is necessary due to COVID-19.

If you leave your job, you can roll over a self-directed 401(k) plan to another qualified retirement plan or IRA, just as you can with any other 401(k) plan. As long as you move your money into another tax-advantaged account, the transaction shouldn't be a taxable event.

It's your money, and you should be able to buy and sell investments as you choose, taking the risks and reaping the rewards. If your employer offers a self-directed 401(k) plan, you can do just that.