New tax law changes as part of the fiscal cliff deal could have a negative impact on portfolio returns in 2013 and beyond, according to Fidelity Investments.

The Fidelity Investments 2013 guide to taxes and Get real: focus on real after tax-returns tackle the question about what to do with higher tax rates and help retirees understand why they may want to adopt a strategy focused on real after-tax returns and not just total return.

"Investors focused solely on what the market is doing for their portfolios are only seeing half the picture," said John Sweeney, executive vice president at Fidelity. "It's the returns they can generate after inflation and taxes that tell the whole story. Fidelity is encouraging investors to sharpen their focus on real after-tax returns, which is what remains after taxes and inflation are accounted for, and not just on nominal pre-tax returns—also referred to as total returns."