The S&P 500 index may rally even higher than this week’s record levels if crosses a key milestone, BTIG chief technical strategist Katie Stockton says.

The stock benchmark needs to end trading higher than 2,135 on two consecutive Fridays to set the stage for a 12 percent increase to 2,400, she told CNBC. The index rose about 0.5 percent to an intraday high of 2,143.16 on Monday.

"For me, it's very important not to see just see a little inch above that, but a confirmation of a breakout," Stockton told the business network. "That's saved me ... to avoid these false breakouts."

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