object-oriented design – How to create rule-based database records?

I create an application in which people meet certain criteria to receive a payment at certain stages. In order to earn these milestones, users will log the activity into a log and, when they have logged a number of activities, an administrator user will be notified to confirm and authorize the payment.

Currently, we plan to create a record associating a person with a milestone whenever someone records the qualifying activity and removes it when changing that total.

I have about a hundred of these steps. Their requirements are always the number X of activity Y.

Since I have so many milestones, what is the best way to check each of them without a lot of statement for loop or nest of 'if'?