Pointing tasks form a significant part of human-computer interaction in graphical user interfaces. We have developed a model to predict the task completion time for pointing tasks for people with motor-impairment. As part of the model, we have also developed a new scale of characterizing the extent of disability of users by measuring their grip strength. We have validated the model by conducting two trials involving people with motor-impairment and in both trials the model has predicted pointing time with statistically significant accuracy.