obviously, this could prove to be a hindrance in the growth of your agency. a monthly retainer fee is paid in advance by your clients to ensure that your services will be available to them for the period covered. the client has a definitive figure each month that they have to pay, and they can budget it in accordingly. for instance, if you are going to spend around 3 hours in a day on that particular client, the calculations will be as follows: let’s assume a standard year, where you work eight hours in a day for five days in a week. there are several important things that you have to care for as well.