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You probably know by now that charitable deductions are tax-deductible. But how about the cost of caring for your pet? Or your kid's clarinet lessons? In select cases, the IRS has permitted taxpayers to deduct off-beat expenses on their tax returns. Here's the key: Those costs must meet certain conditions; they can't just be personal expenses. For instance, these costs might be a qualified medical expense or they are an entrepreneur's "ordinary and necessary" business expense.

"Pets aren't deductible," said Lisa Greene-Lewis, a CPA with TurboTax. "But if there are medical reasons for a service animal, then you can deduct their expenses." This tax season is especially notable because of the Tax Cuts and Jobs Act, which took effect in 2018. The new law roughly doubled the standard deduction to $12,000 for singles ($24,000 for married joint filers), eliminated personal exemptions and limited itemized deductions. Due to those changes, only about 18 million households will itemize in 2018, down from 46.5 million households in 2017, according to the Joint Committee on Taxation. That means it could be harder for filers to claim off-beat itemized deductions on their returns. Nevertheless, here's a sample of some deductions filers have sought — and received from the IRS.

Breast implants

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Generally, you can't collect a tax break for cosmetic surgery. However, in 1994 the U.S. Tax Court allowed an exception in the case of Cynthia S. Hess, then a self-employed exotic dancer in Fort Wayne, Indiana. Hess, who was also known as Chesty Love, underwent a series of dramatic breast augmentation surgeries in 1988. She tried to nab a depreciation tax break on the implants, declaring them a deductible business expense. The IRS initially blocked the deduction, asserting that the implants were a personal cost. However, the Tax Court found them to be a business expense and ruled in Hess's favor.

Private air travel

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Back in 1990, the Tax Court ruled in favor of John and Joana French, who tried to write off on their 1984 taxes on a private plane they used to check on their rental condo. The Frenches were based out of San Jose, California, and their condo was in Mammoth Lakes, California. The two had the choice of driving more than six hours or taking the one commercial flight available in order to look after their property. The IRS had argued that the family enjoyed flying to Mammoth Lakes and that they would ski and swim during their visits, therefore the trips were actually vacations. The Tax Court permitted the write-offs: "We do not consider the expenses here to be unreasonable given the surrounding circumstances, if it is considered reasonable for petitioners to personally manage the condo."

Pet expenses

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The IRS allowed a junkyard owner to deduct the cost of cat food as a business expense. In this case, the taxpayer asserted that the food was necessary to attract feral cats, which kept the junkyard's pests — wild rats and snakes — in check. On the other side of the spectrum, if you have a service animal or guide dog, you can deduct the cost of buying, training and maintaining it. This would count as a medical expense. Finally, if your pet becomes an internet sensation, you might be able to deduct related costs as business expenses, said Greene-Lewis. Be aware that your pet's activities must be considered a business — not a hobby — in order for those expenses to be deductible. The IRS has a nine-part test to help you make the determination, addressing the time and effort spent into making your activity profitable and whether you maintain accurate books and records.

Swimming pools and weight loss

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Here's one situation where a swimming pool isn't just a money pit: Your doctor prescribes it to treat a medical condition. "If your doctor prescribes exercise in a swimming pool and you need it to mitigate a disease, it could be deductible as a medical expense," said Greene-Lewis. The same goes for weight-loss aids that your doctor prescribes to treat a particular illness. This might be deductible, but only to the extent it's not covered by insurance.

Clarinet classes