(Bloomberg Business) -- They're having another go at it: turning your retirement savings into an income stream that will last for the rest of your life.

The problem is simple. You don't know how long you’ll live, so it’s hard to know how fast you can afford to spend your nest egg.

When you retire, you can give your money to an insurance company, which will send you a monthly check for the rest of your life. But annuities' fees can be high and their terms complex, and many retirees don't want to tie up their money. The price of a dependable income into your 90s and beyond is the chance that you’ll die younger and never get to enjoy it. Last year, $229.4 billion in annuities were sold, the Insured Retirement Institute estimates. That’s up 4 percent from 2013 but less than sales in 2009 and earlier, even though the number of retirees keeps rising each year.