Your total account balance will be higher than the original purchase value when set up on an interest-bearing plan.
Any instalment plan longer than 3 months will have interest applied. Each plan will have a calculated total interest applied to it which is added onto your full outstanding balance.
There are interest free options available, just choose a 1 or 3 month plan before you make any payments.
Before you set up or amend an instalment plan you'll be shown the calculations for monthly and total interest applicable. You must ensure you are happy with this before selecting confirm.