Retirement savers have an array of options to maximize tax savings and long-term asset growth. But not all accounts are equal, and certain individuals can turbocharge their wealth-building if their employment status meets certain criteria.

The list below contains seven of the best tax-advantaged retirement savings accounts based on contribution limits, ease of access, investment options and tax savings.

[See: How to Reduce Your Tax Bill by Saving for Retirement.]

Employer-sponsored 401(k). The employer-sponsored 401(k) is top retirement savings account for its convenience, tax benefits and the potential for employer matching. By contributing to a 401(k) automatically each pay period, workers save for retirement and lower their taxable income before receiving their paycheck. The contribution limit for 2017 is $18,000. Workers 50 and older can contribute an additional $6,000.

The Census Bureau estimates that 79 percent of U.S. workers have access to a 401(k) or other defined contribution plan, but only 41 percent of those eligible employees made contributions. Participate in your 401(k) from day one of employment. If your employer has a match, make sure to contribute at least the minimum amount to get the maximum match.

The quality of 401(k) plans varies based on fund selection and fees. Know the expense ratio of each available fund and watch for third-party fees known as 12b-1 fees, which pay for marketing and distribution costs. If your employer’s 401(k) investment selections lack low-cost index funds, contact your human resources department to request additional fund options.

Solo 401(k). One of the most powerful retirement savings accounts is the solo 401(k). The solo 401(k) is ideal for self-employed workers who earn a high income and want to maximize tax-advantaged savings. Like a regular 401(k), the account allows deferral of up to $18,000 pre-tax (those 50 years and older can defer an additional $6,000). The account also permits pretax profit-sharing contributions from their business entity, up to 25 percent of compensation. Combined total contributions must not exceed $54,000 (or $60,000 for individuals over 50).

For example, a self-employed person earning $100,000 in W-2 salary from their own business entity per year can defer up to $18,000 pretax to their solo 401(k) account. The business can then contribute an additional $25,000 pretax, for a total of $43,000.

The solo 401(k) permits a larger annual contribution than a SEP IRA because of how the annual contribution limit is calculated when income level is the same. You can also borrow up to 50 percent of the solo 401(k) account value or $50,000, whichever is lower.

[See: How to Max Out Your 401(k) in 2017.]

Self-directed IRA. The self-directed IRA is useful for people who want to use their IRA money for investments other than stocks, bonds and mutual funds. Common self-directed IRA investing options include real estate, precious metals, private lending, limited liability companies and private equity investments. These accounts are for more sophisticated investors looking to utilize their expertise to outperform traditional IRA investment options.

To invest with a self-directed IRA, you’ll need to set up an account with a specialized custodian who makes investments on your behalf based on your direction. Then transfer funds from an existing IRA, 401(k) or make annual contributions. The account still functions like a traditional IRA in that contributions are pretax, investments grow tax-free and the funds are taxed when withdrawn.

Health savings account. Health savings accounts are common with high-deductible health plans and are meant as a way to pay for medical expenses tax-free. However, an HSA works well as a retirement savings vehicle because savings into the account are tax-deductible like a 401(k) and IRA, funds grow tax-free and funds can be withdrawn tax-free like a Roth IRA. But to make this work, you’ll need to keep good records and think outside of the box.

Qualified medical expenses are typically paid for out of an HSA account tax-free. But there is no time limit on when the account withdrawals must be made, and you aren’t required to use the HSA debit card to pay for a medical expense. Therefore, you can pay for a medical expense with cash or a credit card and save the receipt for the future. Years later, when you want to make a tax-free withdrawal, you have your receipts to do so and can use the money for any purpose.

Investments in the HSA account can then grow tax-free for longer. At age 65, the HSA begins to act like a traditional IRA. Distributions for non-medical expenses are taxed as income. Withdrawals for qualified medical expenses remain tax-free.

Roth IRA. Roth IRA accounts are easy to open and available to anyone earning less than the established income limits. That makes them widely accessible to middle-class workers. Ideally, you want to maximize your contribution to a 401(k) first to lower your taxable income, then contribute to a Roth IRA.

Contributions to a Roth IRA are funded with after-tax money instead of pretax like a 401(k) or traditional IRA. But once the contribution is made, earnings grow tax-free. You can withdraw the original contributions at any time tax-free and penalty-free, but the early withdrawal of any investment gains will be taxed and penalized. At age 59 1/2, withdrawals can be made completely tax-free and penalty-free.

Individuals with a modified adjusted gross income (MAGI) of less than $118,000 can contribute up to $5,500 annually. Between $118,000 and $133,000, the contribution limit phases out. Married couples filing jointly can each contribute up to $5,500 if the combined MAGI is less than $186,000. The limit phases out from $186,000 to $196,000.

[See: 10 Tax Breaks for Retirement Savers.]

Traditional IRA. A traditional IRA is like a 401(k), but it is not tied to an employer and contribution limits are lower. The 401(k) is better because of the higher contribution limits and potential match. But think of a traditional IRA as a utility account with more investment options. The traditional IRA is perfect for transferring money out of a former employer’s 401(k).

For 2017, you can contribute up to $5,500 to a traditional IRA, plus an extra $1,000 if you are 50 or older. Unlike the Roth IRA, traditional IRA contributions are not limited by annual income. But if you have a defined contribution plan at work, deductibility of contributions goes away when your MAGI is more than $72,000 for individuals and $119,000 for married couples filing jointly.

457 Plans. These plans are available to certain state and local governmental employees. The accounts operate in a similar way to the 401(k) with two main differences. First, early withdrawals are not subject to a 10 percent penalty like a 401(k). Withdrawals are, however, taxed as income. Second, if your employer has a 457 and a 401(k), you may contribute the maximum amount to both accounts. That means employees under age 50 can contribute $18,000 to both accounts for a total tax savings of $36,000. Those age 50 and older can contribute an additional $6,000 in catch-up contributions to both accounts, increasing the maximum annual tax savings to $48,000.

Craig Stephens is a blogger at Retire Before Dad.

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