It takes about two weeks to get rid of a modest infestation of cockroaches, but it can take up to eight weeks to get rid of a heavy infestation, according to Pest Kill. However, there is no definitive time frame because of the variance in infestations.
The uncertainty in the length of time is due to the different types of roaches and the varying sizes of infestations. Also, roaches can survive without food and water for 12 days, so it is difficult to get rid of a large infestation completely, according to Pest Kill. A combination of professional killing treatments and removal of cockroach attractants from the home is often necessary.