Few people -- and I'm one of them -- really understand the risks we take when we build our portfolios. Is that biotech stock that climbed 17% last month really worth the risk -- because it might just as easily drop 23% on a day's worth of bad news? Is that cold-as-clay mining stock even riskier -- given that it has returned zilch over the past five years?

A handful of new Web sites will crunch the numbers for you and provide answers to questions like these. Visiting RiskGrades, Total Sum and PortfolioScience.com is a little like taking your portfolio to the doctor for a checkup. You may discover festering problems that have contributed to your performance fatigue, or -- worse -- a ticking time bomb that could send your holdings into arrhythmia at any moment. Here's a quick tour of all three sites.

RiskGrades

This site was launched by a company called RiskMetrics, once a part of J.P. Morgan. RiskMetrics has provided risk analysis on holdings of large institutions since 1994. Enter the stocks, bonds or funds you own, and the site generates a revealing chart that compares the risk levels of each holding vs. its potential rewards. Stocks or bonds plotted above the red line on the chart provide sufficient reward potential for the risks they carry. Those that fall below the red line don't. What could be simpler?

RiskGrades also lets you play what-if games. For example, suppose you wanted to know the risk level of your portfolio if you sold off a certain stock. Just check the "sell" box, and the software rescores your portfolio's overall risk.

At the heart of RiskGrades is a sophisticated calculator that factors in all the nastiness that can affect your portfolio: interest rate hikes, currency fluctuations, market volatility, you name it. When all the numbers are finally crunched, each of your holdings receives a number or score. The higher that number, the more you're living dangerously. The site's builders describe the score as a standardized measure of volatility. And they claim their measure is more descriptive than a beta score (which I'll talk about below).

Moreover, a RiskGrades score would apply equally to a stock on the Singapore Exchange or to one in Paris or New York. In other words, if your epileptic biotech stock received an off-the-chart risk rating of 400 and you owned a Russian banking stock that also scored 400, the two would carry the same level of risk.

One of RiskGrades' cooler features measures how well your portfolio might do if a major bad-news event occurred. The tool even gives you specific examples, such as the Mexican peso crisis, the Asian financial crisis or the "dot.com bomb." Simply select a crisis and you'd get a taste of the pain you'd face.

Total Sum

Total Sum also shows how your portfolio might react to market events, but maybe in a more objective way. As with RiskGrades, the first thing you do is create a portfolio made up of funds, stocks, currencies or indices. Then you can learn what would happen to all of your positions if one of them took a serious hit. For example, let's say your portfolio consisted of equal parts of Microsoft (MSFT:Nasdaq - news), America Online (AOL:NYSE - news) and General Electric (GE:NYSE - news). You could quickly discover how much America Online and General Electric would decline if Microsoft were to suddenly lose half of its value. When I did this calculation, the site told me that AOL would likely decline by $7.22 a share (a 13% fall from Tuesday's closing price), and GE by $6.15 (a decline of 11%).

Alternately, you can enter an index such as the Dow and then tell the calculator to factor in, say, a 1,000-point drop (a mild correction) and see how that would affect your overall portfolio.

Total Sum also tells you how much risk your portfolio will bear over a specific period of time. I entered some stocks favored by active traders, such as Echelon (ELON:Nasdaq - news), Genentech (DNA:NYSE - news) and JDS Uniphase (JDSU:Nasdaq - news). This time I was informed that there was a 95% chance Genentech would not fall by more than $8.59 (a drop of 5% based on Tuesday's close) in a single day. With Echelon the figure was $3.36 (9.3%), and with JDSU it was $6.46 (6%). Of course, the answer implies there's a 5% chance the stocks will fall by more than the amounts shown. You can adjust the holding period from one day to a month or 200 days or whatever.

You can also adjust the odds from the 95% default to, say, 85%. Ironically, this might be a good screen for daytraders who are searching for stocks with lots of volatility.

Portfolio Science.com

Portfolio Science is maybe the most user-friendly of the three. And it seems geared more toward less-experienced investors. Enter your portfolio and the site will show you the risks you face in both dollar and percentage terms over the course of a day, a week, a month or even a year's time. You can also compare your portfolio's risk to holding a simple index such as the S&P 500. One neat feature divides your portfolio into industry sectors and then shows how much risk each of those sectors carries. A simple mouse click creates a Java chart that lines up the stocks you own in order of their risk level.

Beyond Beta

Risk analysis is a fairly arcane field -- one that has been the domain of math geeks up until now. When most of us want to gauge the risk of a stock, we simply call up its beta on sites like Market Edge. A beta measures a stock's volatility relative to the market. Stocks with betas of 1 move up or down more or less in tandem with the market. Stocks with betas of less than 1 tend to be less volatile than the market as a whole. Volatile stocks have betas higher than 1.

As a measure, beta has its limitations, however. If the market itself is volatile to begin with, then a stock with a beta of 1 or less still could give you a scary ride.

The calculators on these three sites dissect risk more thoroughly. All three sites also contain useful tutorials. The one at RiskGrades, in particular, is excellent. Take it and you'll be able to outtalk your insurance agent next time he or she calls.