(That would work out to a rate of 23.8 percent for high-income investors once the health care tax is added on.)

Alternative Minimum Tax If Congress doesn't act soon, about 25 million people next year will experience this arcane tax for the first time, requiring them to pay more to Uncle Sam.

"That has to be a top priority," Steffen said.

The AMT was created decades ago to catch wealthy tax avoiders but was never adjusted for inflation, so even middle-class families now can owe the tax. Congress usually provides a temporary fix to protect the middle class, but the latest patch expired last year.

Many expect a deal to be worked out on the Alternative Minimum Tax by year's end. But if a retroactive fix isn't passed until early next year, that would delay the filing of returns by millions of taxpayers while the IRS updates its system, said Edward Karl, vice president of taxation for the American Institute of CPAs. And that would also delay any refunds those taxpayers are owed.

Estate taxes A last-minute compromise two years ago raised the amount of money that can be exempt from federal estate taxes and reduced the tax rate. An individual now can shelter up to $5.12 million from the estate tax, and amounts over that are taxed at a rate of 35 percent.

Once this expires at year's end, an individual will be able to shelter only $1 million — not hard to reach with a house, insurance and a 401(k). Estates above that limit would be taxed at a rate as high as 55 percent.

There's plenty of chatter about returning to the $3.5 million limit of 2009 with a top tax rate of 45 percent, Steffen said.

Still, Steffen noted, the country "never had a situation where the exemption falls from one year to the next," which could complicate estate plans. For simplicity, he said, Congress might keep the current exemption limit.

Wealthy households, though, aren't taking any chances, experts say. They currently can make gifts totaling $5.12 million without triggering gift taxes, and some are doing so quickly to reduce the size of their estates in case the law changes.

Payroll tax Workers for the past two years have contributed 4.2 percent of their wages up to a certain level for Social Security — down from the traditional 6.2 percent. This tax break, which disappears next year, saved workers an average of $1,000 a year.

Until a few weeks ago, this was one tax break that neither side seemed interested in keeping, said Schwab's Townsend. Now some Democrats have been raising concerns about the loss of this tax break for the working class. One suggestion, he added, is to ease the transition by raising Social Security contributions by 1 percentage point next year.

Still, among the tax cuts politicians will fight to retain, this one remains a long shot.

401(k) contributions Next year, workers can set aside up to $17,500 on a pre-tax basis in a 401(k). Those 50 and older will be able to salt away an extra $5,500. That's potentially $23,000 in income that workers will be able to postpone paying taxes on.

Changes to this tax-friendly plan are unlikely to occur next year, said Craig Rosenthal, a partner in Mercer's retirement, risk and finance business. But as Congress looks for ways to raise revenue and slash the deficit, it could lower contributions to this retirement account, he said.


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