When would a 12 month fix end?

CBX1985

I usually go for a fixed rate gas/electricity fix until a set daye 'i.e. 31st May. When, rather than this, it is described as fixed for 12 months, when does that 12 month period end? Twelves Months from date of application or when the switch completes?

I appreciate it is strange question, but I'm a high volume user and it could alter my calculations substantially.

molerat

Usually 12 months from start of supply.