Subscription based on actual year, not on length

[Jorg]

I searched the forum but no success. I'm looking for a way to have a subscription for our federation that works as follows:

Members pay a fee each year (15 euro) and they become member for that year. So if they pay in january or in july, their membership ends on december 31st. Also people who subscribe in the last 3 months of that year get those last months for free and already pay for the next year; someone subscribes on october 15th 2005, they stay a member untill december 31st 2006.

Anybody any idea how I can accomplish this?