Minimum fee is 30 days.
If you purchased a 90-day subscription and cancel before the 90 days expire the refund is based on the cost of a 30-day subscription with the difference refunded to you (to your credit card if you paid on line). Seven days constitutes a 30-day subscription. If your subscription is 47 days, you would pay for two months and the remained would be refunded. If the subscription is 35 days, you pay only for a single 30-day subscription
Subscriptions of 180 or 365 days which are cancelled are refunded based on days in force. If it is 60 days or less, then the charge is based on 30 day periods (where 7 days defines a 30 day period). If it is 90 days or longer then it is 90 days plus 30-day increments. If it's greater than 180 days then the charge is for 180 days plus 30-day periods or 90-days periods depending on the total number of days subscribed.