Monthly store credit or purchase credits?

[JuseBeats]

I want to give a store credit when someone becomes a member. And with every month, an additional credit is applied. I also want the credit to expire after a month (Use it or lose it). So it's the same amount available every month.

I would imagine it could give the credit based off the tag given to customer. So as long as they are tagged, they get credit deposited again. Is this possible?