Investor advocates are reminding their clients not to get too heady about cash flow figures if they are bolstered in part by certain tax incentives.

RiskMetrics Group analyzed bonus depreciation being claimed by public companies as a result of the American Recovery and Reinvestment Act earlier this year and the Economic Stimulus Act of 2008. The firm estimates bonus deprecation will boost operating cash flows for qualified investments by about 14 percent in the first year, but will reverse in the following year to nick flow by about 5.6 percent of qualified investments.

Bonus depreciation is a provision that enables a corporate taxpayer to accelerate normal depreciation, which accelerates the related deductions for tax purposes. It doesn’t reduce the ultimate tax bill, but defers it into future tax periods. That deferral translates into a current boost in cash flow, but a reversal of that cash flow increase when the tax bill finally comes due in a future period, said Zhen Deng, an analyst with RiskMetrics.

Some companies specifically disclosed the impact of bonus depreciation on cash flow, said Deng, while others weren’t as explicit. The research uses some raw data and some extrapolation to arrive at the conclusion that the impact to cash flow could be material for some companies, she said. That means investors should take note of cash flow figures and look for the impact of bonus depreciation, she said.

“We’re not necessarily saying companies are hiding it, but for companies that elected bonus depreciation provisions either in 2008 or 2009 or both years, there is a component of operating cash flow that is not sustainable,” she said.