The length of the agreement depends upon the type of variable rate you have chosen. Details of your agreement will be on your agreement documentation in your welcome pack.
If you have chosen a day-to-day agreement, the length of that agreement will be shown on your documentation.
If you've chosen a balanced payment agreement then the length of your agreement will depend on how interest rates move over the period. If interest rates go down then your payments will complete early. However, if interest rates rise then your monthly payments will continue after the scheduled end date.
For information on specific agreements please contact customer services.