There is an allure to saying you bought a stock on the first day it ever traded. But it’s not necessarily practical.

The initial public offering is rarely the stock’s lowest price. Shares seldom make their market debut, shoot up and never come back down to their initial offering price.

Don’t expect to be able to buy shares at the offering price, either. Those are reserved for company insiders and others connected to the IPO.

Typically, a much-anticipated IPO does bounce higher on the first day of trading. Its rally can continue for a few days or even weeks. But then the stock takes a breather and starts to decline.

This sets up its first base. Look for buying opportunities when the new issue breaks out from that first base, rather than chasing it on the first day or week it goes public. With a chart pattern to work with, you have a better sense of when to buy.

Bases of new stocks can be unusual, though. They can be shorter, deeper or wilder than normal. Yet the strength of a fast-growing new company can quickly boost shares.

While most proper bases are at least six or seven weeks long, American Commercial Lines (ACLI ) formed just a three-week base before it broke out in November 2005.

In three weeks, there’s little to work with for chart analysis. There is no 10-week moving average yet, no clear areas of support or resistance.

American Commercial shares surged 180% in 69 weeks.

Other stocks, such as eBay (EBAY ), have formed deep initial bases. When the online auction house went public in 1998, the offering price was just 18 a share. It was a great deal, considering that shares hit 54.25 on the first day.

But ordinary investors never had a shot at 18 a share. The stock gapped up at the open, and the low on the day was 44.25. After four days of not doing much, it began its correction.

The market was weakening. In three weeks, eBay was down 54%. There are no bragging rights in buying a stock only to watch it lose 54%.

But after four weeks, the stock formed a V-shaped base. This was an IPO base that investors would have missed if they had been applying the rules for normal bases.

EBay’s pattern was deep and short. But it was powerful: Shares soared 1,194% in just 27 weeks.

With IPO bases, remember to give them latitude. They don’t behave like normal bases.

Keep track of what stocks have recently gone public by checking New Issue America, a feature that appears some Tuesdays in IBD. Also, a table of new issues often appears in The New America.