Regardless of which subscription length you choose, the subscription is always paid in advance. Automatic subscription renewal is activated by default if the purchase is done via a credit card or PayPal account.
If you pay for a six-month subscription (€8.33/month), you will be charged €49.98. Once the payment has been received, 6 months of subscription time (186 days) is added to your account.
The same rule applies when buying a 12-month subscription (€7/month). You will be charged €84. Once the payment has been received, 12 months of subscription time is added your account (366 days).