found this on the website
Q: Why isn't my predicted progress displaying on my progress graph?
A: The predicted progress 'blue line' works using the last 4 weeks of weight information. If your average weight change is a maintain or a gain, a predicted date won’t show.
Alternatively, if you haven't set your target weight the blue line won't be displayed. To set your target weight, go to ‘My Slimming World > my personal achievement target from the top navigation menu, and you’ll see the ‘enter your target weight here’ link
so i guess i need to wait......