The other half of retirement planning - how much will you spend?

The trillion-dollar floodgates haven't opened yet, but soon 76 million baby boomers will want their money back from the retirement accounts they so carefully fed.

They'll have many questions: What are the mechanics for making that money last? How can they live on it for 25 or 30 years and still leave something to the kids? How can they manage the interplay of taxes, retirement accounts, Social Security benefits, and housing decisions to make the most of their cash?

The financial services industry is starting to help, with new products ranging from withdrawal-focused mutual funds to new annuities. Some are more helpful than others, and folks who are coasting toward retirement should put at least as much effort into planning their withdrawals as they did when they planned their contributions.

It's a big topic, but here are some ideas that can get you started:

Investment advisers can tell you what stocks to buy but typically don't have the grasp of Social Security, life expectancies, taxes, and pension law an actuary will. Furthermore, actuaries work only for hourly or project fees when they crunch your numbers and won't have their recommendations clouded by commissions or a desire to manage your nest egg.

You can find an actuary at actuarialdirectory.org or by searching your local yellow pages. Call a few, ask if they've had clients with similar needs to yours, and get references. You can ask them questions about when to start claiming Social Security, how much to withdraw from your tax-deferred, taxable, and tax-free accounts every year, and more.

The way that Social Security benefits are taxed can add a real burden, says Ron Gebhardtsbauer of the American Academy of Actuaries.

You can find the calculations, in all their complexity, at the website of the National Center for Policy Analysis (ncpa.org/pub/st/st283/st283f.html).

The short version of it is this: Once your retirement income, including half of your benefits, crosses the $25,000 mark for singles ($32,000 for couples), you'll be paying taxes on some of your benefits.

Once your income, including half your benefits, is $34,000 (singles) and $44,000 (couples), your tax burden gets even heavier; as much as 85 percent of your benefits will be taxed.

If you're in the 25 percent bracket and subject to that top tax threshold, it means your marginal rate will be 46.25 percent. With most of your retirement income coming from tax-deferred accounts like 401(k)s or IRAs, you can expect to be pushed into a taxable situation. It makes some offbeat strategies - like converting from a traditional IRA to a Roth IRA, or liquidating your taxable retirement accounts early - seem more sensible.

Perhaps you've seen tables putting your life expectancy at 80 or 85. But, as any actuary would tell you, that only means you have a 50-50 chance of dying before then. A couple in which both partners are 65 today have a 58 percent chance of at least one of them still being alive at 90, and a 28 percent chance of one of them making it to 95. If you need your money to last forever, you probably can't take more than 4 percent a year out.

Annuities can help

Putting some of your cash into an immediate annuity will often increase your spending power. Because annuities pool risk, they can afford to pay out more than that 4 percent level you're stuck with because of your own uncertainty about life expectancy, says Dan DeKeizer of MetLife Retirement Strategies Group. A 62-year-old woman could buy an annuity that would pay her 4.7 percent for life; a man could get 5.2 percent. But you can't put all of your money into annuities, lest you need large chunks of it for medical emergencies or a grandchild's tuition.

Vanguard Investments and Fidelity Investments have introduced mutual funds for retirees that are designed to yield regular income. They automatically pull a predetermined percentage from your account every month and mail you a check. Most fund companies will put any of your other mutual funds on autopilot for withdrawals. But don't use your whole annual draw in monthly installments, or you won't have enough money when you need a new roof.

Linda Stern is a freelance writer. She can be reached at lindastern@aol.com.