(MONEY Magazine) – QUICK: HOW MUCH MONEY DO YOU HAVE IN your 401(k) or 403(b) retirement plan at work? If you're a serious investor, or simply a worrier, you may be able to answer that question with reasonable accuracy. Now try this one: How much do you have in your company's traditional defined-benefit pension plan?

Unless you work for one of the approximately 4 million companies that don't offer a defined-benefit plan--in which case the answer is unfortunately easy--you're probably stumped. Defined-benefit plans, which require no contribution from you and promise to pay a specified income after you retire, are the mysterious strangers of the pension world. Because the responsibility for investing the money and paying those benefits rests entirely on your employer, you may not give your plan a first thought, let alone a second one. But if you don't, you're ignoring a key element of your financial future. To get a sense of how important your defined-benefit pension may eventually become, take a look at the chart below.

With all the news reports of companies curtailing or even eliminating benefits, you may well wonder whether you should include your defined-benefit pension in your retirement planning at all. The short answer: You should. "For one thing, if you keep track of your pension every year, you're more likely to catch a mistake--say, a mathematical error or the use of an incorrect salary figure," says financial planner Alan Cohn of Bala Cynwyd,Pa."The later you catch an error, the more difficult it can be to get it fixed."

As many recent retirees have learned to their disgust, however, you also shouldn't assume that your plan will pay every cent you've been promised. To protect yourself from a major reversal when you retire, get answers to these five crucial questions now:

1. How soon will I qualify for benefits? In general, if you're at least 21 years old, you'll start accruing benefits once you have completed a year of service. However, you probably won't have any claim on that money until you're vested--that is, you've worked for the company long enough to qualify for benefits. Employers can choose one of two vesting schedules. If your boss has picked cliff vesting, you become 100% vested after five years of service. With graded vesting, you become at least 20% vested after three years, 40% after four years and so on, until you are completely vested by the end of year seven.

Your plan's administrator, usually someone in your employee-benefits office, is required by law to provide you with a summary booklet that describes your pension, including its vesting schedule. You should also ask the administrator to calculate the current value of your accrued pension every year.

2. What happens if I retire early? Nearly all defined-benefit plans offer early-retirement payouts, says actuary Raymond Sharp of Buck Consultants in Secaucus, N.J. Typically, you can retire with some benefits at 55 if you've put in 10 years of service. But don't expect to join the high rollers at Monte Carlo. By and large, if you quit at 55, your pension may be only about half as big as it will be if you continue working until age 62. (Sixty-two is considered full retirement age under most plans.) And if you work until 65, as the chart shows, your pension will be larger still.

If your plan lets you take a lump sum at 62, as about 10% of companies do, one rough way to estimate its value is to multiply 1 1/2 to two months' worth of your final salary by the number of years you worked for the company. Thus if you earn $4,000 a month when you retire and you've worked for the company for 30 years, your lump sum will fall between $180,000 and $240,000 ($6,000 or $8,000 times 30). If you take your pension as a lifetime annuity instead, you'll get about $1,800 a month for life.

If you plan to retire at 55, estimate your pension by multiplying your years of service by one month's worth of final pay. So even if you have worked at the company for 30 years, you'll get a lump sum of only $120,000 or a monthly annuity of $900.

3. What happens if I quit or get fired? Assuming you're vested, the pension benefit you have accumulated up to the day you leave belongs to you. That may not be a whole lot of money, however, especially early in your career. A 40-year-old with five years of service who earns about $46,000, for example, typically will have amassed only $6,690 in the pension fund.

4. Is my plan adequately funded? "You hear horror stories about underfunded pensions, but that's not the norm," says Sharp. "The vast bulk of corporate plans are very well funded." Still, one person in five (about 8 million people out of the 41 million covered by private defined-benefit pensions) is in a plan considered underfunded by the Pension Benefit Guaranty Corporation, the government agency that insures private pensions. That means if the company went bust today, the plan wouldn't have enough money to pay all the benefits it owes.

To find out whether your plan is on shaky ground, read the Summary Annual Report (SAR) automatically sent each year to members of plans with 100 or more participants. (If you are in a smaller plan, you'll receive a report every three years.) "You can usually tell from the SAR how secure your pension is," says Cindy Hounsell, staff attorney for the Pension Rights Center, a nonprofit advocacy group in Washington, D.C.

In particular, check to see if your plan has lost a large amount of money since its last report. If it has, the summary should provide a reasonable explanation. Also look for unduly high administrative costs (greater than 3% of total plan assets), which may be a sign of mismanagement. Hounsell's group offers a booklet, Protecting Your Pension Money, that explains how to check up on your plan. (For a copy, send $8.50 to Pension Publications, Suite 704, 918 16th St. N.W., Washington, D.C. 20006.)

5. Will the Pension Benefit Guaranty Corporation back my pension? The PBGC insures 56,000 private pension plans sponsored by single employers or, in some cases, groups of employers. Most employers pay the PBGC an annual premium of $19 per participant for coverage. Your plan's administrator can tell you whether your pension is insured.

In 1994, the PBGC paid $720 million in benefits to 172,800 people covered by 1,961 failed plans. Benefits are capped, however, and this year the maximum is $2,642.05 a month. So, many retirees wind up with less than their plans have promised. Moreover, only people who retire at 65 or older are eligible for the maximum amount. Those who retire at 62 get no more than $2,087.22 a month this year; at 55 it's $1,188.92.

That's another reason--just in case you needed one--to keep pumping as much money as you can into your 401(k) and other retirement savings accounts. Then if your defined-benefit plan comes through as promised, your retirement will be all the richer.