A fixed period subscription means that, regardless of when someone purchases the subscription, they will receive a subscription that starts on the day that they purchase the subscription, and ends the number of days later that you have specified for the subscription. Note: The day that they purchase the subscription is the day on which their order is updated to status Payment Received, not the date on which they placed the order.
A fixed end date subscription means that, the members subscription will expire on the end date that you have specified for the subscription product. Use this if you want all of your members' subscriptions to expire at the same time. When creating the subscription, select from the dropdown the length of time a full subscription would run for (either annual or monthly). Monthly subscriptions always run from the first to the last day of the month. For annual subscriptions, select the day of the year you want all of the subscriptions to expire on. Click here for details about members purchasing/renewing their subscriptions during the subscription period. Fixed end date subscriptions have a rollover period. Members who purchase during the rollover period will receive a subscription that runs until the end of the following period.