I have adopted a smoothed 10MA to reduce the noise on this data series from Thomson Reuters. Last week's 10 MA of 17x forward earnings was 2205 and this week up to 2213. I especially like this because the non MA version seems to show a drop in earnings estimates for last week which is probably not correct.
17.5x 10MA = 2280, up from 2270
18x 10MA = 2343
20x 10MA = 2603
There you have it, a continually updating target range for SPX at 18x - 20x forward earnings. I don't think the market is going higher than that.
Based on 12/16 close, this means SPX about 4-15% upside from here, although it is possible that the 10MA will continue to climb and this shift the target range higher as well.
Citigroup Economic Surprise Index has worked very well, leading the market on the summer breakout up, the stall, and then the post election rally. If bullish then this needs to stay in positive territory for a while. It is the nature of "expectations" to shift over time, so even if strong markets there are some swings up and down. Still, better for stock & interest rate bulls for this to stay above zero.