WASHINGTON - Higher-income Americans and some legally married same-sex couples are likely to feel the biggest hits from tax law changes when they file their returns in the next month or two. Taxpayers also will have a harder time taking medical deductions this year.
In other changes, the tax rate tables and the standard deduction have been adjusted for inflation, as has the maximum contribution to retirement accounts, including 401(k) plans and Individual Retirement Accounts.
The Alternative Minimum Tax has been patched - permanently - to prevent more middle-income taxpayers from being drawn in. And starting with the 2013 tax year, there's a simpler way to compute the home office deduction.
Tax provisions for the 2013 tax year were set by Congress last January as part of legislation to avert the fiscal cliff of tax increases and spending cuts. "We finally got some certainty for this year," said Greg Rosica, a contributing author to Ernst & Young's "EY Tax Guide 2014."
Nevertheless, the tax filing season is being delayed because of the two-week-long government shutdown. The Internal Revenue Service says it needed the extra time to ensure that systems are in place and working. People will be able to start filing tax returns Jan. 31. Before the shutdown, the original start date was Jan. 21.
"People who are used to filing early in order to get a quick refund are just going to have to wait," said Barbara Weltman, a contributing editor to "J.K. Lasser's Your Income Tax 2014."
Don't think the delay will mean a change to the tax deadline, however. "The April 15 tax deadline is set by statute and will remain in place," the IRS says.
The tax legislation passed at the start of 2013 permanently extended the Bush-era tax cuts, but also added a top marginal tax rate of 39.6 percent for those at higher incomes - $400,000 for single filers, $450,000 for married couples filing jointly and $425,000 for heads of household.
On top of that, higher-income taxpayers could see their itemized deductions and personal exemptions phased out and pay higher capital gains taxes - 20 percent for some taxpayers.
And, there are new taxes for those taxpayers to help pay for health care reform.
However, there are different income thresholds for each of these new taxes.
The additional 0.9 percent Medicare tax, for example, kicks in on earnings over $250,000 for married couples filing jointly and $200,000 for singles and heads of household. Same for the 3.8 percent tax on investment income.
But the phaseout of personal exemptions and deductions doesn't begin until $300,000 for married couples filing jointly and $250,000 for singles.
That means that taxpayers who didn't plan could find themselves with big tax bills come April 15 - and perhaps penalties for under-withholding.
"It's a snowball effect," said Dave Du Val, TaxAudit.com's vice president of customer advocacy.
"The complexities of the tax code are only affecting those of us trying to read it," National Taxpayer Advocate Nina Olson said in an interview. Tax software makes a lot of those complexities invisible to the average taxpayer.
As a result, taxpayers might not realize they're being helped by a wide array of deductions and credits. "They have no idea of the benefits they are getting through the tax code," she said.
Taxpayers will still be able to deduct their medical expenses, but it will be more difficult for many to qualify. The threshold for deducting medical expenses now stands at 10 percent of adjusted gross income, up from 7.5 percent. There's an exception, though, for those older than 65. For them, the old rate is grandfathered in until 2017.
Among the other changes for 2013, taxpayers who work at home will now have a simplified option for taking a home office deduction.
"You can claim this deduction for the business use of a part of your home only if you use that part of your home regularly and exclusively," the IRS says.
But, if you sit at your kitchen table and check work email, it doesn't qualify. "The regular and exclusive business use must be for the convenience of your employer and not just appropriate and helpful in your job," according to the agency.
Beginning this year, same-sex couples who are legally married will for the most part have to choose married filing jointly or married filing separately when doing their tax returns. This is true even if the couple lives in a state that does not recognize gay marriage. "For federal tax purposes, the IRS looks to state or foreign law to determine whether individuals are married," the agency said.
Once again, the IRS is reminding taxpayers to make sure their Social Security number is entered correctly and their return is signed. Those who feel they need more time can apply for an extension, until Oct. 15. But if you do file for an extension, remember to estimate and make sure you pay any taxes due - or face a possible penalty.