AbstractWe investigate the tidal interactions between hot Jupiter extra-solar planets and their host stars in an effort to characterise the effects of such interactions on stellar rotation. We study the WASP-18 and WASP-19 systems, showing that in both cases tidal interactions cause the eventual spiral in of the the planet towards the Roche limit. We find that for both systems this process will cause significant spin up of the host star, independent of the precise value for the tidal quality factors. By fitting tidal evolution models to observed parameters, we are able to determine that WASP-19 b is currently spiralling in, and that it has a very short remaining lifetime ~ 3 Myr.