Most married couples file their taxes jointly, and who can blame them? It's usually easier to prepare one tax return than two, and it almost always results in a lower tax bill than filing separately. But sometimes, splitting up those returns might make sense financially.

The lowdown on filing jointly

There are rules to follow for filing separately.

If one spouse itemizes instead of taking the standard deduction, for example, the other spouse must itemize, too. You'll also have to decide which spouse gets each deduction, and that can get complicated. Plus, there are a bunch of deductions and credits you probably won't be allowed to take if you file separately, such as the credit for child and dependent care expenses, the earned income credit, the adoption credit, education credits and the deduction for student loan interest.

And there's another rule: You must get the vocabulary right. Filing separately isn't the same as filing single. Only single people can file single, and their tax brackets are different from the ones that will apply to you if you're married and filing separately.

Nonetheless, in the right circumstances, being married and filing separately could save you money. Here are a few things to think about if you're considering whether it's right for you.

Student loans

If you're enrolled in an income-based student loan repayment plan, filing separately could reduce your monthly bill. Income-based repayment programs generally key off adjusted gross income, or AGI. If you file separately, your payments are in many cases based only on the borrower's income rather than on your joint income as a couple. That's a big consideration that makes it worth the time to calculate your taxes both jointly and separately. It could be worth filing separately and paying an extra $500 in April, for example, if you're going to save $200 a month in student loan payments.

High earners

The general strategy behind filing separately is that the parts may be worth more than the whole. If you and your spouse are high earners, this is particularly relevant, because many deductions and credits phase out above certain AGIs.

For the 2016 tax year, for example, the IRS starts limiting itemized deductions for joint filers with combined AGIs of more than $311,300 (in 2017 it's $313,800). For high earners, filing jointly means potentially lost deductions and credits and the possibility of a higher tax bill. Filing separately might keep each of you under those phase-out thresholds and thus lower your tax bill. So, if you're a high earner, it might be worth the extra effort to calculate your returns both jointly and separately to see which will save you more.

Medical expenses

Generally, you can deduct medical expenses -- but only the portion that exceeds 10 percent of your AGI. If you're 65 or older, you can deduct medical expenses that exceed 7.5 percent of your AGI for the 2016 tax year. Either way, filing separately could make more of those expenses deductible.

Here's an example. Let's say you and your spouse are both 30, and one of you racked up $9,000 in medical bills last year. If you file jointly and your combined AGI is, say, $100,000, then only the portion of your medical bills over 10% of that -- or the portion over $10,000 -- is deductible. So in this scenario, you can't deduct a penny of your $9,000 in medical bills because you filed jointly.

Now let's say you file separately. Your AGI is, say, $75,000 and your spouse's AGI is $25,000. Now the math may work in your favor, because anything more than $7,500 (that's 10 percent of your AGI) is deductible. If you were the one with the medical bills, filing separately just got you a $1,500 deduction. Alternatively, if the medical bills belong to your spouse, he or she could deduct anything over 10 percent of that $25,000 AGI, or $2,500. That would mean a $6,500 tax deduction for filing separately.

Complicated spouses

If your spouse brought overdue taxes into the relationship, it may be worth filing separately. That way, the IRS won't snatch your refund away and apply it to your spouse's overdue bill. Remember, however, that in most cases filing separately means a higher overall tax bill for both of you. So if the goal is to keep your tax bills low, the better choice may be to fork over that refund and get that liability out of your hair.

If you're getting a divorce or you suspect your spouse isn't being upfront about tax matters, you should think about filing separately, too. After all, once you sign that joint return, you have joint liability. You may be able to get "innocent spouse" relief from the IRS if things explode, but convincing the IRS that you're innocent isn't easy.

What's yours is mine

If you're thinking seriously about filing separately, there's one more thing to understand: Even if you do the math and determine you'll pay less by filing separately, state law might throw a wrench in your plans. That's because if you live in a community property state -- Arizona, California, Idaho, Louisiana, Nevada, New Mexico, Texas, Washington or Wisconsin -- anything couples earn generally belongs to both spouses equally. Couples filing separately there each have to report half of the income both spouses earned, which could nullify most of the advantages of filing separately.

Tina Orem is a staff writer at NerdWallet, a personal finance website. Email: torem@nerdwallet.com

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