How long do you have to tax your vehicle?

How long do you have to tax your vehicle?
In UK every year.

EDIT: Just to expand the above answer a little. In the UK you MUST have continuous tax on a vehicle. Your new tax disk takes over from the expiring one. You do not have a 'period of grace' whereby your existing tax disc has expired and you've not 'had time' to get the new disc validated. As soon as your existing tax-disc expires - if you drive the vehicle on the road - you will get a ticket if you're stopped by the police. That includes driving from your home to the post office to renew the disc ! As soon as a vehicles tax expires, the DVLA computer system notifies the Police National Computer and a marker is put against the vehicle's registration to say the tax is no longer valid.