The fee is paid at the same time as your monthly savings contribution. No fee is charged on the pre-paid month(s).. 

We charge a fee so that we can provide you with an excellent and efficient experience. Carbon is providing the infrastructure and guaranteeing that you will be paid as long as you stay up to date with your payments, even if the other participants in your group do not. Plus everything is seamlessly integrated with your Carbon account so you don’t have to worry about manually making payments.