I have some news for you, folks: You are not entitled to a retirement. It's not in the Constitution. It's not in the Bill of Rights. It's not in the Bible (except for that one time in Numbers 8:25, and that was only for the Levites). Retirement is something you earn.

You have earned your Social Security benefits, but good luck retiring on those. This year, the average benefit is about $13,000 a year -- and let's not even get into whether future benefits will be paid in full.

Not only are you not entitled to a retirement -- you don't deserve a retirement. By "you," I mean the average American -- which could mean you specifically if you're doing an average job of planning for your retirement. Here are three reasons why you should work for the rest of your life.

1. You don't save enough.
According to the Federal Reserve, the savings rate in this country hasn't exceeded 5% since 1995; that's down from approximately 12.5% in early 1981. There's plenty of debate about whether the savings rate accurately reflects how much people are actually saving. But there's no doubt that the average American isn't saving enough.

Hey, it's a free country. You earned your money, you should spend it however you like. But if you're spending every dime you make throughout your career, don't complain when your 60s roll around and you're still a slave to the alarm clock.

2. You don't know how much you need to save.
What's one of the best ways to get someone to save more for retirement? Get them to do a retirement savings calculation. According to the Employee Benefit Research Institute, crunching the numbers is particularly effective at getting people to make a change to their retirement plan. Unfortunately, less than half of workers even bother trying to estimate if they're saving enough.

On our Rule Your Retirement website, we have a host of calculators to help you analyze several financial decisions, including a retirement calculator that can handle all kinds of variables -- Social Security, pensions (and whether they adjust for inflation), different levels of spending in retirement, and Roth and traditional retirement accounts, to name a few. Your broker or IRA provider might also provide a retirement calculator; just make sure it can handle all the moving parts.

But whatever calculator you use, you'll at least have some idea of what you need to do -- especially if you're in your 40s and 50s and are way behind.

3. You have a lousy portfolio.
As we've seen over the past several months (and past several years), U.S. stocks don't always go up. Which means your portfolio hasn't done so much, if your portfolio -- like those of most other Americans -- is dominated by the stocks of large American companies, thrown together with no rhyme or reason.

However, there's a whole world of other investments out there, and holding a little bit of different types really paid off over the past decade. Consider that a $100,000 investment in an S&P 500 index fund in the beginning of 1998 was worth $177,546 by the end of 2007, a 5.9% annualized gain. However, what if that one hundred grand was instead invested in the following portfolio and annually rebalanced?

Asset Category (25% in each)

Typical Stocks

U.S. Large-Cap Stocks

Microsoft (NASDAQ:MSFT), AT&T (NYSE:T)

U.S. Small-Cap Stocks

Walter Industries (NYSE:WLT), Comstock Resources (NYSE:CRK)

International Stocks

Novartis (NYSE:NVS), Sony (NYSE:SNE)

Real Estate Investment Trusts

Public Storage (NYSE:PSA)

Source: Large caps and small caps from Ibbotson Associates; REITs from NAREIT index; international from Europe, Australasia, and Far East Index. "Typical stocks" taken from respective Vanguard index funds.

That portfolio turned $100,000 into $251,463, for an annualized return of 9.7%. Plus, it has held up much better so far during this painful year.

Finally, if you're within 10 years of retirement, or already retired, you should own bonds, with a heavy dose of inflation-protected securities. The iShares Lehman TIPS Bond exchange-traded fund is up around 12% over the past year. Have anything like that in your portfolio?

Begin earning your retirement
You won't be able to retire until you have a plan -- a plan for how much you'll save now, a plan for how you'll invest those savings, and a plan for the best ways to spend it if and when you actually can retire. In my Rule Your Retirement service, we cover those topics each and every month -- along with model portfolios and the best ways to maximize your Social Security, pension, and retirement accounts -- with some cool tools thrown into the deal. You can check it out with a free 30-day trial by clicking here.

With a lot of planning now and a little maintenance planning along the way, you'll get the retirement you deserve.

This article was first published July 11, 2008. It has been updated.

Robert Brokamp would like to stay, but he has to see a horse about a man. He owns none of the stocks mentioned in this article. Microsoft is an Inside Value recommendation. The Fool has a disclosure policy.