Itemized deductions will be reduced for individuals earning more than $250,000 and couples earning more than $300,000 a year. People making more than $400,000 a year and couples making over $450,000 will face the highest marginal taxes on income (39.6 percent) and capital gains (20 percent) in addition to the 3.8 percent Medicare surtax. At that point, taxpayers even lose their personal exemption — the $3,900 deduction people and their dependents get just for being alive.

“The calculations are getting more complicated,” said Monica Rebella, a certified public accountant in Southern California. “It’s going to be small things that get people.”

For example, losing the personal exemption for a family of four means $15,600 in deductions just disappeared, she said.

The first thing people need to do is assess where they are on the ladder of tax increases. In figuring this out, the traditional planning techniques of accelerating or delaying income, deductions and state taxes can keep your income from cracking one of the income levels that will increase your tax bill.

But there are several things people can’t control. Ms. Rebella pointed out that take-home pay has already gone down for people who have earned $200,000 to date. That is because companies are required to start withholding the 0.9 percent Medicare tax above that amount.

This should be straightforward, but it has at least two complications. If those people are married and their spouse’s income does not put them over the $250,000 threshold, they should not have to pay the tax. But since it is a Medicare tax and not an income tax, Ms. Rebella worried that the systems set up to calculate the two different taxes may not work together and the refund will be lost.

The second issue is if the other spouse earned, say, $180,000, which would put the couple well over the $250,000 limit. Because the 0.9 percent tax would not have been withheld from that spouse’s income, the couple will end up owing more.