Provided payment has been received, a TV Licence is valid until the expiry date shown on it. TV Licences normally last for a year. They expire at the end of the month and your licence starts on the day you buy it. For example, if you buy a licence today it will cover you for up to 12 months - the rest of this month and 11 months after that. Then if you renew your licence on time next year it will run for a full year. If you renew late it may not last a full 12 months.
TV Licence expiry dates stay the same each year. This means that if you buy a licence at any time in September it will start straight away and expire on 31 August the following year. Then, in following years it will always expire on 31 August.
Setting end-of-month expiry dates keeps TV Licensing’s collection costs down and means more money is invested in the BBC’s programmes and services.