I have just renewed my subscription a few days before it was due to expire. I was very surprised to see that the renewal took effect from the time of renewal and not from the end of the previous subscription. I am not too concerned, just a few pence difference. However it does not give a good feeling that your system takes advantage of my wanting to renew at a safe and convenient time.
If you value customer satisfaction above scraps of profit I suggest you change that aspect of the renewal system.
S