Chances are that you’re not taking all the tax deductions to which you’re legally entitled—leaving money on the table, in other words.

That’s because the category of medical costs that are tax deductible includes a lot more types of expenses than most are aware of, according to Eric Smith, a spokesperson for the IRS.

Did you know, for example, that this category includes expenses as diverse as acupuncture, fertility enhancement, and weight-loss programs? (The full list appears in this IRS publication.)

Perhaps the least understood category, however, deals with home health care costs. That’s unfortunate, because that category that not only happens to be one of the biggest but also growing quite rapidly, as you can see from the accompanying chart.

As always, you should consult your own tax adviser rather than relying on this or any other investment column. But below is a summary of what Smith told me in an interview.

You must itemize

It might seem obvious, but it’s worth emphasizing nonetheless: You must itemize your deductions in order to deduct home health care costs. Furthermore, you are allowed to deduct those and other medical and dental costs only to the extent they total to more than 7.5% of your adjusted gross income.

That shouldn’t be too big of a barrier, however, since home health care costs can be substantial. Eight hours a day of care from a home health agency could easily cost close to $100,000 a year, for example.

Who qualifies?

In order for home health care costs to be deductible on your taxes, either you or one of your dependents must require assistance in at least two of the “activities of daily living” (ADLs). The IRS defines the ADL category to include “eating, toileting, transferring, bathing, dressing and continence.”

The health care costs must be pursuant to a plan of care prescribed by a licensed health care practitioner. Note that this practitioner need not be a medical doctor.

Read: Smart advice for Medicare open enrollment

Which expenses qualify?

Allowable tax deductible expenses include all “necessary diagnostic, preventive, therapeutic, curing, treating, mitigating, rehabilitative services, and maintenance and personal care services.”

This is a broad category, and it sometimes is not clear which expenses are deductible. A general rule of thumb for what is and is not included: Is the expense for a service you’d otherwise expect to receive in a nursing home for a patient who needs assistance in at least two ADLs? If so, then its expense generally should be tax deductible.

That’s because nursing home expenses are themselves tax deductible if the patient needs help with at least two ADLs. In the course of providing that care, of course, a nursing home of necessity also provides a number of household services—such as cooking, cleaning, laundry, and so forth—that are not paradigmatically medical expenses. But, because there is a medical necessity for the patient to be in that nursing home, those ancillary expenses also become tax deductible.

The IRS recognizes that the same tax treatment should apply if someone chooses to receive the equivalent care at home rather than in a nursing home. Allowable costs, according to the IRS, include those for services which have “as its primary purpose the providing of a chronically ill individual with needed assistance with his or her disabilities (including protection from threats to health and safety due to severe cognitive impairment).”

Keep copious records

Finally, don’t forget that you need to be able to document all your expenses. This includes documentation of the prescription for home health care from a licensed health care practitioner.

The bottom line? As you decide whether, after developing disabilities that require assistance on at least two ADLs, to stay at home with the help of a home health care service, be sure to focus on your after-tax costs. You may be fortunate enough to discover that you can, after all, afford the necessary level of that outside care.

For more information, including descriptions of the Hulbert Sentiment Indices, go to The Hulbert Financial Digest or email mark@hulbertratings.com.