Gains on corporate 'inversions' may mean higher tax rates on some 2014 returns. Associated Press

Many investors will see spikes in income this year as a surge in corporate deals generates unexpected payouts. That could trigger a surprising spike in their tax rates, too.

The U.S. tax code rescinds tax benefits and adds surtaxes for higher earners, typically those with incomes of more than $150,000 a year. These are essentially backdoor tax increases, and the effects can vary greatly. Investors who are at risk should run their individual numbers or consult a professional while there is still time to make moves this year that could soften the blow, experts say.

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It has been a banner year for mergers,with global deal activity up 56% over 2013 by dollar value, according to Thomson Reuters. The takeovers of Micros Systems, Hillshire Brands and Furiex Pharmaceuticals will include taxable cash payments to shareholders.

Another dozen or more firms, including AbbVie, Medtronic and Burger King Worldwide, are planning "inversions," where U.S. companies merge with foreign firms and move to lower-tax countries. Investors holding stock in taxable accounts—as opposed to a tax-sheltered retirement plan—often get a windfall due to an inversion because it is treated as a sale, along with a surprise tax bill.

In addition, energy giant Kinder Morgan has announced a reorganization that could generate income for many holders of units of Kinder Morgan Energy Partners, its widely held master limited partnership.

The result could be that some income and capital gains could be taxed at substantially higher rates.

Chris Hesse, an accountant at CliftonLarsonAllen in Minneapolis, researched how backdoor tax increases change the tax rates on investment income for a typical family of four as long-term capital gains are added to an income of $80,000 of wages and $20,000 of interest.

He found that a wide swath of people with a nominal tax rate of 15% on long-term gains actually owed nearly 28% on the gains.

The impact is likely to be most significant for people with incomes between $150,000 and $500,000, says Mr. Hesse. When the typical family's income rose above $500,000, the actual rate on long-term gains flattened to about 24%, he found.

Taxpayers who are most affected by these backdoor tax increases sometimes have the most room to avoid them, if they act in time, says Scott Kaplowitch, an accountant at Edelstein & Co. in Boston. He recently advised a client with a deal-related windfall that waiting to take deferred compensation until next January will cut his tax rate on the income by 10 percentage points, as the client will have retired by then and be in a lower bracket.

Here's a brief guide to the main backdoor tax increases and some ways to limit the resulting bills.

Alternative minimum tax. The AMT was originally imposed to keep the wealthy from taking too many tax breaks, although now it falls most heavily on the affluent. It works by eliminating certain benefits, such as the personal exemption and state and local tax deductions, and limiting the value of others.

While capital gains aren't penalized by the AMT, having a high proportion of long-term capital gains to ordinary income can trigger the levy, says Mr. Kaplowitch. So a taxpayer who plans to make charitable donations over several years might be able to lower the capital gain and avoid the AMT by making several years' worth of gifts of appreciated stock to favorite charities all at once.

If the AMT is unavoidable, however, it might make sense to postpone donations to a future year, when they will be more valuable—and to accelerate state tax payments into this year to reduce the likelihood of triggering the AMT again next year.

Net investment-income tax. This flat levy of 3.8% applies to the amount of net investment income, including dividends, capital gains and interest, that a taxpayer has above a certain threshold. It is pegged at $250,000 of adjusted gross income, or AGI, for most married couples and $200,000 for most singles, and it isn't adjusted for inflation.

While the 3.8% surtax typically doesn't apply to quarterly payouts made to investors by master limited partnerships such as Kinder Morgan's, experts say it will apply to the income generated by reorganizations such as the one Kinder Morgan plans.

The best way to limit this levy is to keep AGI below the threshold. Itemized deductions such as mortgage interest don't help, but putting income into a tax-deductible retirement plan or deferring income to a future year could. Making a charitable gift of appreciated inversion stock could also reduce the portion of a long-term gain that raises AGI.

Personal Exemption Phaseout. The PEP restriction takes effect at $305,050 of AGI for most married couples and $254,200 for most single filers.

PEP rescinds the value of the $3,950 deduction that is allowed for each family member. It disappears entirely at $427,550 of AGI for most couples and $376,700 for most singles—if the taxpayer isn't subject to the AMT, which disallows the deduction entirely. For that reason, PEP is more likely to affect people with higher incomes from low-tax states who aren't caught by the AMT.

The best way to avoid PEP, say experts, is to keep AGI below the threshold, using the same methods that can work for the net investment income tax.

Pease limitation. This provision takes effect at the same threshold as PEP. It reduces most itemized deductions, such as those for mortgage interest, state and local taxes, and charitable donations, by 3% of the amount over the threshold—although it can never take away more than 80% of a taxpayer's itemized deductions.

In practice, experts say, the Pease limitation can add up to 1.2 percentage points to a taxpayer's overall rate. Taxpayers who can't keep their AGI below the threshold should review the timing of deductions that are flexible, such as for charitable donations, says Mr. Kaplowitch.