Lousy returns on your investments during the first few years of retirement can greatly increase the chance you'll outlive your savings.

That's a big new concern for anyone who wants to retire and didn't move most of their money out of the stock market and into safer, less volatile bonds and CDs over the past few years.

You may need to spend less, or even postpone retirement, according to the Wall Street Journal.

For example: A retiree with a $500,000 portfolio -- invested 55% in stocks and 45% in bonds -- who withdraws 4% in the first year and increases that amount by 3% annually to adjust for inflation has an 89% chance of having enough money to last for 30 years, according to T. Rowe Price.

But if the portfolio returns less than 5% a year during the first five years of retirement, the chance a retiree will run out of money sharply increases.

With annual returns of 4%, the chance the fund will last 30 years falls to 74%. With returns of 2% to 3% a year, it drops to 64%.

Declining home prices -- which have tumbled as much as 20% in some cities after peaking in 2006 -- aren't helping, either. If the value of a $600,000 home with a $300,000 mortgage drops 15%, the home's equity falls 30%, from $300,000 to $210,000.

Current retirees may be tempted to get out of the market until things stabilize, but for the best long-term gains, it's important to be invested when a rebound begins.

Instead, T. Rowe Price says you should reduce your withdrawals until returns bounce back.

If you're not sure how much you'll need for a secure future, our retirement calculator can help you figure that out.