Low from Feb 9, 2018 reached 2532.69
The S&P index is down -61 points now and traded to a low of 2536.23. That is within about 4 points of the February 9 low price of 2532.69. A move below that level will look toward the 50% retracement of the move up from the November 2016 low.
Meanwhile the Nasdaq index is down -181 points or -2.63% with a low at 6722. The low price for 2018 for it reached 6630.67 back also on February 9th.