Dear Liz: My wife and I are about 35. I’m self-employed and contribute to a SEP IRA. My wife contributes to a workplace retirement plan. We don’t qualify to contribute to Roth IRAs. In order to get more money into retirement accounts, would you recommend doing back-door Roth contributions? What else is there to do to get retirement money into accounts that will have a tax benefit now or later?

Answer: Roth IRAs don’t provide an upfront deduction, but withdrawals are tax-free in retirement. That makes them especially enticing to people who expect to be in the same or higher tax bracket in retirement — mostly higher-income people and good savers.

People who earn more than certain limits, however, are prohibited from contributing directly to a Roth IRA. For 2018, direct Roth contributions aren’t allowed for people whose modified adjusted gross incomes exceed $199,000 for married couples filing jointly or $135,000 for single filers.

Several years ago, however, Congress eliminated income limits on who was allowed to convert a regular IRA to a Roth IRA. That change created the back-door Roth strategy, in which a high-income taxpayer contributes to a regular IRA and then converts the money to a Roth.

The strategy works best for people who don’t already have a large IRA filled with pre-tax contributions and earnings. When you convert all or some of an IRA to a Roth, you have to pay a proportionate amount of income taxes on the conversion based on all of your IRA holdings. If you don’t have an existing IRA and don’t deduct the IRA contribution, you’ll owe little if any taxes on the conversion.

The IRS hasn’t specifically blessed or banned the back-door Roth strategy, so it remains somewhat controversial. Many investing and brokerage sites promote it. Some proponents, however, recommend letting several months pass between the contribution and the conversion. The idea is to avoid IRS scrutiny by making the transactions appear to be separate decisions rather than one clearly meant to get around the contribution limits.

If you want to stay out of gray areas and potentially contribute more cash to your retirement, consider setting up a solo 401(k). This version of the popular workplace plan is meant for self-employed business owners with no full-time employees other than themselves and their spouses. Plan participants under age 50 can contribute up to $18,500 a year. Those 50 and older can contribute up to $24,500. The plan can have a Roth and an after-tax contribution option in addition to a pre-tax option. In addition, the business can make a 25% annual profit-sharing contribution (or 20% if the business is a sole proprietorship or single member LLC). The combined maximum of participant and business contribution is $55,000 for those under 50 and $61,000 for those 50 and older.

If you’re able to contribute more than these amounts each year, consider a traditional defined-benefit pension. Those involve considerable set-up and ongoing costs, so consult a tax pro to see if it’s a good fit.