Flexible spending accounts (FSAs) offer workers a potentially sizable tax break. And while these accounts come with certain restrictions, in most cases, it pays to open one. Here are a couple of things you should know going into 2018.

1. FSA limits are increasing for next year

For the current tax year, FSA participants could allocate up to $2,600 in pre-tax dollars to cover out-of-pocket medical expenses. The good news is that this limit is increasing to $2,650 for 2018, which means you'll get a slightly bigger tax break if you choose to max out.

Woman paying at the pharmacy

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So should you max out? It depends whether you think you'll incur enough qualified medical expenses to make doing so worthwhile. The IRS maintains pretty strict rules regarding what you can and cannot claim against your FSA.

For example, you can easily claim the deductibles you pay toward your health insurance, dental, and vision plan. You can also deduct your copays for visiting healthcare providers, as well as those you pay toward prescription medications. Keep in mind, however, that over-the-counter medications don't count toward your balance unless you have a prescription for them. Furthermore, most dietary supplements aren't FSA-eligible, unless, again, you have a letter of medical necessity to accompany your purchases.

Medical equipment is another expense that's typically eligible for FSA reimbursement. If you need a blood pressure or blood sugar monitor, for example, those can count toward your balance. Similarly, if you wear prescription eyeglasses or contact lenses, you can use your FSA dollars to pay for them. Finally, don't forget that travel expenses to and from medical appointments qualify as FSA-eligible as well.

How much can an FSA save you? It depends on your effective tax rate, but if yours is 30%, and you max out your FSA next year, you'll shave $795 off your tax bill. And that's not a small amount of savings.

2. FSA participants usually forfeit unused cash -- but not always

FSAs typically operate on a use-it-or-lose-it basis, so that if you contribute too much in a given year and don't rack up enough eligible expenses, you'll forgo whatever money is left in your account by the time your plan year comes to a close. However, there are two special provisions that allow employers to give participants more flexibility, should they choose to do so: the carryover option and the grace period option.

Under the former, FSA participants can carry up to $500 of unused funds from one plan year to the next. Under the latter, participants get an extra two and a half months to use up their unclaimed funds. For example, if we're talking about a plan year ending on Dec. 31, 2018, employers offering the grace period would allow participants to rack up expenses until March 15, 2019. Keep in mind that employers can't offer both a carryover and a grace period; rather, they must choose one or the other. Either option, however, will only work to sweeten the deal for those who enroll.

3. You may have the option to change your plan election in 2018

Typically, when you enroll in an FSA, you're required to commit to a single amount for your entire plan year. That's why it's critical to accurately estimate your healthcare expenses and arrive at a contribution that makes sense for you. But if you experience a qualifying life event, such as marriage or the birth of a child, you can typically adjust your allocation after the fact.

So let's say you just submitted your FSA election for 2018 and then learned that you're pregnant. Once you have a child, you'll have the option to increase your contribution to cover your additional medical expenses.

If your employer offers a flexible spending account, it pays to enroll for 2018. You'll save money on your taxes, which will only help offset the hefty healthcare costs so many of us face.

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