Let's say you have a $300,000 nest egg and expect your essential expenses in retirement -- shelter, utilities, transportation, food, health insurance, etc. -- to be about $2,300 a month. Your Social Security check might provide $1,600 of that amount. If you're a 66-year-old man, you could buy an immediate annuity from Vanguard for $100,000 that would pay you about $727 a month for life. If you wanted inflation protection -- in other words, a payment that would rise along with the cost of living -- your guaranteed initial check would drop to $554. (You can play with the numbers yourself at Vanguard's annuity website.)

You could use what's left in your retirement accounts to provide the "extras," such as travel or a new car. The annuity would ensure that you could pay your basic living costs even if your investments turned against you or you lived longer than you had expected.

If you opt for the annuity route, you'll want to make sure the insurer you pick has rock-solid finances and low expenses.

10. Stress-test your plan

You now should have enough facts and figures to see if your plan will work. Garrett recommends using a post-retirement return rate of no more than 6% or 7%. That's the historical norm for a relatively conservative portfolio of stocks, bonds and cash.

"You want any surprises to be on the upside," Garrett said.

Then consider checking out T. Rowe Price's retirement income calculator, which can estimate your plan's probability of succeeding.

What if you're falling short? See what would happen if you worked a little longer, or adjust your budget to see whether you could live on a little less. If you're determined to retire and the numbers don't work, consider more-drastic options, such as moving to a cheaper area or a smaller home.

11. Meet with a fee-only financial planner

The decisions you're about to make are too important to your future not to get a second opinion. Look for an objective planner who's experienced with retirement-income calculations.

You can get referrals from Garrett's organization, the Garrett Planning Network, or from the National Association of Personal Financial Advisors.

12. Review your estate plans

Your chances of being incapacitated -- too ill or injured to make your own decisions -- rise as you age. Make sure you have updated durable powers of attorney for finances and for health care (the latter document is known as a health care directive in some states), so that someone you trust can take over for you.

Also consider a living will, which outlines what kind of end-of-life care you'd want if you weren't able to speak for yourself. Though they're not as foolproof as they're often portrayed, they can give your loved ones a road map for what you might have wanted.

Dealing with these issues can be difficult and emotional, Garrett said, so don't try doing it while you're sitting in your attorney's office. She recommends getting a copy of the workbook brochure "5 Wishes," available for $5 from Aging With Dignity, and taking time to review your options. (Another nonprofit group, HELP, has free resources at its website.)

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You also should review any wills or trusts and update beneficiaries on retirement, bank and investment accounts and on life insurance, preferably with the guidance of your attorney and financial planner.

"If you haven't updated your will since the kids were born," Garrett said, "now's the time."

Liz Weston is the Web's most-read personal-finance writer. She is the author of several books, most recently "The 10 Commandments of Money: Survive and Thrive in the New Economy" (find it on Bing). Weston's award-winning columns appear every Monday and Thursday, exclusively on MSN Money. Join the conversation and send in your financial questions on Liz Weston's Facebook fan page.