) -- Retirees have long struggled with a difficult question: How much can you spend annually without going broke? Financial advisors have suggested that typical investors can start by spending about 4% of their assets annually. So an investor with $1 million can withdraw $40,000 the first year. After that, retirees can raise their annual payouts along with the inflation rate. But in recent years, advisors have begun to question the traditional advice. Now some researchers suggest withdrawal rates of less than 3%.

Retirees should tighten their belts because of current market conditions, says David Blanchett, head of retirement research for Morningstar Investment Management. He says that many investors should only withdraw 2.7%. Blanchett says that earlier studies of withdrawal rates assumed that markets would deliver the same returns in the future as they had done in the past. But there are now good reasons to think that returns in the next decade will be subpar.

Blanchett estimated that intermediate government bonds will return 1.8% annually in the next decade, compared to the long-term figure of 5.5%. The reason for the gloomy outlook is that bond yields are currently low. Yields account for nearly all the returns produced by bonds. So when yields are low, returns are skimpy. Blanchett did his calculations in December 2012 when the yield on 10-year Treasuries was 1.8%. Today the 10-year Treasury yields 2.7%. The higher yield should help returns, but the 10-year outlook remains well below the historical average.

From 1926 through 2011, the

S&P 500

returned 11.8% annually, according to Ibbotson Associates. It is possible that stocks will continue the double-digit pace, but Blanchett says that markets have often delivered much smaller returns. To be on the safe side, he assumes that stocks will return 9.8% annually. Using that forecast, a retiree who has 60% of assets in equities and 40% in bonds could be in danger of exhausting assets. If the retiree uses a withdrawal rate of 4.3%, there is a 50% chance of spending all the money in 30 years. By lowering the withdrawal rate to 2.4%, the retiree has a 95% chance of avoiding bankruptcy over 30 years.

Mutual fund company T. Rowe Price takes a brighter view, suggesting that investors can increase withdrawals by tweaking the traditional 4% system. To avoid running out of cash, investors should examine their holdings once a year. If a portfolio lost money during the 12 months, then the retiree should forgo an inflation adjustment for the next year.

Say the investor withdrew $50,000 the first year of retirement and the inflation rate is 2%. Under normal circumstances, the retiree would make the inflation adjustment in the second year and withdraw $51,000. But if the portfolio lost money, the retiree would forgo the adjustment and only take $50,000. If the market then shows gains, the saver can resume the inflation adjustment in the third year. By skipping the inflation adjustment, the retiree can stretch assets. The researchers found that investors who sometimes forgo inflation adjustments can afford a withdrawal rate of 5.1%.

Another way to increase the withdrawal rate is to combine the inflation tweak with a system that considers market valuations, says T. Rowe Price. If stocks are cheap, investors can spend more. Researchers found that when stocks are unloved, their returns in the next 30 years tend to be high. If stocks are rich, the following returns are poor. This does not mean that investors should jump into cheap markets and expect to get outsized returns in the next year. Instead, cheap stocks tend to offer an advantage that becomes clear over decades.

Researchers looked at a hypothetical saver with a 60-40 portfolio who started making withdrawals at a time when the price-earnings ratio of the S&P 500 was less than 10. Because the valuation was low, the retiree could use a withdrawal rate of 7.5%. If the P/E ratio topped 17.4, the saver could only use a rate of 4.8. With the market multiple currently more than 20, retirees should consider trying a cautious withdrawal rate.

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This article was written by an independent contributor, separate from TheStreet's regular news coverage.

Stan Luxenberg is a freelance writer specializing in mutual funds and investing. He was executive editor of Individual Investor magazine.