If you are self-employed and trying to boost your retirement savings, you may want to consider Solo 401(k) plans.

Solo 401(k) plans are qualified retirement plans for self-employed professionals and business owners with no employees. These plans have gained popularity because of investor-friendly features and high contribution limits.

The biggest limitation on a Solo 401(k) plan is its eligibility criteria. You must have some sort of partial or full-time self-employment, and you can't have any full-time employees — except your spouse — working in the business.

For an owner-only business, it presents an option for ensuring your savings are sufficient to fund your retirement years.

Is a Solo 401(k) right for you? Here are four reasons it's worth considering.

1. High contribution limits. Unlike individual retirement accounts, which limit contributions to $5,500 (or $6,500 for those 50 and older), you can contribute up to $54,000 to a Solo 401(k) account in 2017 ($60,000 for 50 and older).

2. More options. Relying on the market for retirement may not sit well with investors who prefer to have more flexibility and freedom to choose different types of investments.

With a specific kind of Solo 401(k) called a self-directed Solo 401(k), you can invest in alternative assets including real estate, tax deeds, tax liens, mortgage notes, private equity, personal lending, precious metals and even regular stock-bond investments. Make sure to ask your Solo 401(k) provider about the availability of these options up front.

3. Roth, minus the income limits. According to the current IRS regulations, if you are a single filer earning more than $132,000 in a calendar year, you are not eligible for Roth IRA contributions. The phasing out starts at $117,000, limiting your options for after-tax contributions. A Roth Solo 401(k), which doesn't have income limits, allows you to make annual after-tax contributions of up to $18,000, or $24,000 if you are over 50, giving your money an opportunity to grow tax-free.

4. Ability to borrow. The IRS allows borrowing from a Solo 401(k) plan, just as it allows borrowing from 401(k) plans. This means no one can turn you down and you can spend the money the way you want. Just make sure you follow IRS rules about repayment to avoid taxes and penalties. And loans from a Solo 401(k) hold one advantage over loans from a regular 401(k). With a 401(k), the loan will become due in full if your employment changes. That's not a factor with a Solo 401(k) loan.

Dmitriy Fomichenko, president of Sense Financial, wrote this for NerdWallet, a personal finance website.