Millions of elderly Americans now live in pricey assisted-living homes, and millions more grown children must decide whether to send their parents to one soon. Some get tax breaks, but others do not.

Q: My 92-year-old father entered an assisted-living home earlier this year, when three different doctors agreed he no longer could care for himself after a stroke in November left him partially paralyzed and his Alzheimer’s continues to worsen. The assisted-living home is expensive (almost $4,000 per month), but the wonderful staff there provides all his meals, limited medical help, washes his clothes and bathes him regularly. Can the cost of the facility be deducted as a “medical expense” on Dad’s next federal income-tax return?

A: Some taxpayers can take deductions for the cost of living in an assisted-living facility, but others cannot.

Generally, the Internal Revenue Service permits write-offs for most long-term care expenses if the services provided are for preventive, diagnostic, treatment or rehabilitative purposes.

The cost of personal care (including the cost of having someone else prepare meals or bathe the resident) usually can be deducted if the person is considered “chronically ill.” People usually are considered chronically ill if a doctor or similar professional says they cannot physically or mentally perform at least two activities of daily living for 90 days without significant help from another.

The key here is to remember that any assisted-living or other medical-related expenses typically must be prescribed by a licensed health-care practitioner before they can become deductible. That means that if a grown child decides to put a parent into a facility without first getting the approval of a medical pro, the costs usually cannot be written off.

Your letter states that you put your father into the facility based on the recommendations of three doctors, and he seems to meet all the other requirements for his expenses to be tax-deductible. If so, remember that you can deduct only the amount that is not reimbursed by Medicare or other insurance, and that the write-offs are limited to the amount that exceeds 7.5 percent of his adjusted gross income.

It’s obvious that the rules concerning such deductions are complex, so it’s equally vital to consult an accountant or other tax professional for details. Also, get a free copy of IRS Publication 502, “Medical and Dental Expenses,” by downloading it from the agency’s Internet site (www.irs.gov) or by calling the agency toll-free at (800) 829-3676.

Q: I heard a short report on the radio last week that said some rich Wall Street guy has paid $103 million for a 40-acre estate in East Hampton, N.Y. Is this the highest amount ever paid for a home?

A: No. The $103 million that Ron Baron, founder of financial-services giant Baron Funds, recently paid for the 40 acres of ocean-view property in the swanky Hamptons resort area of New York indeed is a record for any residential-oriented transaction -but there’s not even a mansion on the land!

Baron hasn’t disclosed much about the estate he plans to build. Records show that the parcel was sold by Adelaide de Menil, heiress to the Schlumberger oil empire, and her husband.

The amazing price that Baron paid for the mostly vacant parcel easily surpasses the previous mark for a residential property that was established in 2004, when a 33,000-square-foot home on a “mere” four oceanfront acres was sold for $70 million in ritzy Palm Beach, Fla.