Every promotion usually has a rollover requirement attached to it, and you need to take that into consideration before taking advantage of the promo.It does have an impact of your free play bonus, so here is the information about the calculations.
The rollover requirement equals the sum of the amount you deposited and the amount you get as a bonus multiplied by the amount of rollover. The requirement of the rollover tells you how much you have to bet before your entire free play bonus becomes available to you in full.