If you’re a baby boomer nearing Medicare age and still working with a health savings account (HSA) through your job, you might wonder: Can I keep my HSA after I join Medicare?

According to Medicare financial experts, you can continue using the funds already in the account tax-free for medical expenses not covered by insurance. However, the key point to remember is that once you sign up for Medicare, you can’t make new contributions to your HSA. Many out-of-pocket medical costs are still eligible for tax-free withdrawals from your HSA even after you’re on Medicare.

Some retirees use HSA money to pay for Medicare Part B, Part D prescription coverage, or combined Medicare Advantage plans—but not for Medigap premiums. HSAs are also used to cover co-pays, deductibles, out-of-pocket costs for prescriptions, dental and vision care, and long-term care insurance premiums (which were $3,500 for those aged 61 to 70 in 2012).

So, are HSAs worth having as you approach Medicare age? It’s a matter of personal judgment, says Paul Fronstin, a Medicare specialist with the Employee Benefit Research Institute (EBRI). “You can pay for your healthcare expenses now or later, but there is no free lunch,” he explains.

Should you delay Medicare enrollment to keep contributing to your HSA? This depends on your situation. If you work for a small employer, you usually need to enroll in Medicare when you first qualify, even if it means losing the HSA tax benefits. Small employer healthcare plans often pay second to Medicare, so putting off Medicare could leave you with little to no coverage when you retire.

On the other hand, large employer healthcare plans typically pay primary, so Medicare might not be necessary yet. If you’re working for a large employer and want to delay Medicare Part B, you can do so and sign up later when you lose your current coverage. However, you can’t delay Medicare Part A. If you’re not collecting Social Security benefits when you become eligible for Medicare, you need to actively enroll during your initial enrollment period. Regardless, once you have Medicare, you cannot contribute to your HSA.

If retirees don’t enroll in Medicare when first eligible, they need to be cautious when they eventually collect Social Security. Stop HSA contributions at least six months before applying for Social Security because Medicare Part A retroactively covers up to six months if you’re eligible. Contributing to your HSA while having Medicare can result in a tax penalty.

“Never contribute to your HSA while you have Medicare benefits,” Fronstin advises. “Otherwise, you might face a hefty tax bill.” To avoid this and for more information on eligible expenses, check IRS Publication 502 on Medical and Dental Expenses.