Beware the Ads of November!

A critical time for investors, a momentous event in financial advertising: It's on the way, and it has nothing to do with future market performance or what happens in your portfolio.

What's coming is the 10th anniversary of the stock market crash of October 1987.

And although Oct. 21, 1987 was a Black Monday for investors at the time - the Dow industrial average lost more than 500 points - Oct. 21, 1997 looks like a bright Tuesday for mutual fund companies.

They are readying ads full of charts and impressive percentage gains for their funds.

Come Nov. 1, mutual funds will be able to trace their 10-year performance record back to the October 1987 low - and a chart that starts in a hole is bound to impress.

Consider these numbers, prepared as of Sept. 30 this year: Fidelity's Magellan Fund has returned 15.42 percent a year if you trace it back to the beginning of October 1987, but a whopping 19.28 percent a year if you measure from Oct. 31, 1987. Lipper Analytical Services found similar gaps - 2 to 4.5 percent - for each of the 10 largest mutual funds.

Don't let the statistical quirk fool you. In fact, if you're investing in a taxable account, the end of the year can be a costly time to put a lot of money into a stock fund. Typically December is when funds pay out capital-gains distributions for the year, so you might have to pay taxes on gains that happened before you invested.

So mutual fund investors, beware the ads of November!