There is really no answer for that it depends on a lot of things, type of heat source, thermostat itself, tubs, substrate, where the thermostat is placed, ambient room temp that could affect the probe etc.
I have some thermostat that are set to 80 and provide a hot spot of 83 (Colubrids)
I have some T-Stat set on 88 and the hot spot is at 88, I also have some set on 94 and the hot spot is at 88.