You can use this calculator to estimate a race time, based on another race. Enter your time and distance for a recent race, along with an upcoming target race which you would like an estimated time for.

Race distance:	kilometresmiles
Time taken (Hours, Minutes, Seconds):	: :
Target race distance:	kilometresmiles
Estimated time:

I have found this calculator to be very accurate in the past, if you put in the required training. Perhaps this calculator should be an indication of potential, as opposed to an all-out predictor. If you enter a time for a half-marathon, you can't expect it to give you an accurate time for a full marathon if you haven't done the training. It's very useful to gauge where you are under-performing.