The S&P 500 is rolling over, and this chart signals that the index can fall 18% from current levels.

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The highs of the 2000 dot-com bubble and 2007 housing bubble formed a double top, and after successfully breaking above that resistance level in 2013, the S&P 500 ran up to its 161.8 Fibonacci retracement level, based on the 2007 highs and 2009 lows. Now the S&P 500 is poised to revisit the double top price level and establish it as support. From current levels, the 1,560 price target represents an 18% drop.

The healthcare and energy sectors have helped fuel today's selling in the markets. Both sectors need to establish a meaningful bottom before the market can constructively move higher. The IBB index should find support near $276, representing a drop of 5.5% from current levels. 

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 XLE has more room to fall until it reaches its next level of support. A $50 price target would represent an 8% drop from current levels.

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This market sell off has been a long time coming. The market correction in August 2015 took ~1,400 days to occur; on average, a market correction occurs every 200 days. While corporate earnings are falling and global growth looks anemic, the market is not in doomsday mode similar to the 2008 market rout. A market correction, even a bear market (defined as a 20% drop from highs), is healthy for this 6+ year bull run. Technically, stocks are a buy at the 1,560 for the S&P 500.