Bottom 3 after 18 games:
21/22: Norwich (R), Newcastle, Burnley (R)
20/21: Sheffield United (R), West Brom (R), Fulham (R)
19/20: Norwich (R), Watford (R), Aston Villa
18/19: Fulham (R), Huddersfield (R), Burnley
17/18: Swansea (R), West Brom (R), Newcastle
Over the last 5 seasons, 11 of the 15 sides that were in the bottom 3 after 18 games got relegated (73%).
Of the 4 teams that weren't in the relegation zone after 18 games and still got relegated, 3 of them were in 17th place.
It might be impossible to get relegated in January but it gives a pretty clear indication of where you're going to finish.