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

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

When you retire, you can give your money to an insurancecompany, which will send you a monthly check for the rest of yourlife. But annuities' fees can be high and their terms complex,and many retirees don't want to tie up their money. Theprice of a dependable income into your 90s and beyond is the chancethat you’ll die younger and never get to enjoy it. Last year,$229.4 billion in annuities were sold, the Insured RetirementInstitute estimates. That’s up 4 percent from 2013 but less thansales in 2009 and earlier, even though the number of retirees keepsrising each year.

A generation of “managed payout funds,” launched in 2007 and2008, was supposed to be the solution. But hardly any investors usethem.

Now, Natixis Global Asset Management is launching a “retirementspending account” designed to deliver a predictable monthly checkto retirees for life, and as millions of baby boomers get ready toretire, there are signs that other fund companies and retirementplan providers are also working on new retirement incomeproducts.

An investment account is more flexible than an annuity: Ifthere’s an emergency, you can sell it. If you die young, your heirsget the proceeds. But there's no guarantee it will last if you livelonger than you expect.

Natixis addresses that uncertainty by adjusting its product'srisk as investors get older. Because a market downturn early inretirement can really screw up your plans, the product’sinvestments are conservative for the first years of retirement. By15 years in, almost half the investments are in stocks, which areriskier than bonds but provide bigger returns. That should help themoney last longer, said Edward Farrington, executive vice presidentof retirement at Natixis. Then, as investors move throughtheir 80s and 90s, the product gets more conservative again, topreserve money for heirs.

Natixis investors can choose to get either 4 percent or 5percent of their accounts’ assets each year, in monthly checksadjusted annually for inflation. To get the 5 percent payout,though, investors need to take more risk, raising the odds that themoney will run out in their later years.

Another downside to the Natixis product is its annual fee ofabout 1 percent of assets per year. Because it is sold only throughfinancial advisers, that’s on top of any fee they charge for theiradvice.

Managed payout funds, an older effort to deliver retirementincome, are simpler versions of the Natixis product. They don’tadjust investment risk as you get older, but they do provide amonthly income. The largest, the Vanguard Managed Payout Fund, aimsto give a 4 percent payout, with the payments adjusted each yearbased on performance over the last three years. It's cheaper thanthe Natixis fund, with a fee of 0.42 percent a year.

So far, managed payout funds have collected just $2 billion to$3 billion in assets, Morningstar analyst Jeff Holt estimates.Compare that to the $25 trillion in all U.S. retirement funds,according to the Investment Company Institute. Last year, Vanguardfolded three different payout funds into one. “They really didn’tgain much traction,” Holt said of the whole category.

It remains to be seen if the Natixis product, which went on saleFriday, can do much better. It may have some new competition, too.American Funds, the third-largest U.S. fund company, has filedpaperwork to launch “retirement income portfolios” in threevarieties, “conservative,” “moderate,” and “enhanced.” Spokespeopledidn't respond to requests for comment. Others seem to be on theway, Holt said. “A lot of fund managers are at the drawing board,”he said, and as of now “there doesn’t seem to be a clearanswer.”

One solution would be an easier way to mix investment funds andannuities. Retirees could get a guaranteed monthly check, alongwith a small fund for emergencies or inheritances. Last year,regulators at the U.S. Treasury and the Department of Labor made iteasier for retirement plans to do this. They want 401(k)s to start including annuitiesthat would pay a guaranteed income to workers when they retire. Sofar, no one’s taken them up on the idea.

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