BusinessWeek has this online under Retirement.
Brett Hammond, TIAA-CREF's chief investment strategist, has designed an easy way for employees to check on retirement readiness based on their asset-to-salary ratios at different points in their career. "The big problem is that there is no magic number for the amount of money you need," Hammond says. "This is an attempt to address the needs of real people. If you tell me your assets, income, and age, I can tell if you're on track for retirement."

Hammond's calculations start with one of the basic tenets of retirement planning—that people need at least 70% of their pre-retirement income during post-working years. He states corporate employees with higher income might need 60% from their 401(k)s, with Social Security filling in the extra 10% gap. The wealthier you are, the smaller the percentage of retirement income Social Security will contribute.

How will you know if your nest egg will cover 60% of pre-retirement income once you stop working? If you're 35 and plan to retire at 65, you need 2.1 times your salary to be on track. By 45, you had better have 3.6 times. At 55, the multiple rises to 5.4 times. And by the time you retire, you'll want it to be 7.7 times.

Of course, there are some assumptions built in to Hammond's formula. He assumes a 10% contribution rate, including any employer matching contributions; 4% salary growth, a bit ahead of inflation; a 6% return on investments; and a 25-year retirement period to finance, which would be paid for by purchasing a low-cost annuity at retirement. Those are relatively conservative assumptions—except, perhaps, the 10% contribution rate.

So for example if you are earning $100,000 and are 45 years old, you should have $360,000 in retirement saving to be on track for retirement. According to this calculation I am on track for retirement but I am planning on saving even more to better my chances of a successful retirement.

How is your nest egg doing?