Balance Transfer Savings Calculator

What this tool calculates

A balance transfer card moves an existing card balance onto a new card that charges a low or zero promotional rate for a limited period, in exchange for a one-off transfer fee. This calculator runs a full month-by-month amortisation for both options — staying on the current card at its standard rate, or transferring to the new card at the promotional rate — using the same monthly payment in both scenarios. The result is the net interest saved (or net extra cost incurred) once the fee, the promo period, and the rate that applies after the promo are all included.

How the simulation runs

For the stay scenario, the calculator applies the current monthly rate to the running balance, adds the monthly payment, and repeats until the balance reaches zero. The total interest accrued across all those months is what staying actually costs. For the transfer scenario, the upfront fee is added to the principal, the promotional rate is applied for the promo months, and once that period ends the rate reverts to the original card's rate — the standard assumption for any balance still outstanding. Total interest under each scenario is then compared, with the transfer fee added to the transfer-side cost.

What moves the savings figure most

The single biggest lever is whether the balance clears within the promotional window. When the monthly payment is large enough relative to the balance to clear it before the promo ends, the only effective cost on the transfer side is the fee, and savings are typically large. When the balance does not clear in time, the residual amount accrues interest at the revert rate — which by default is the same rate the card had originally — and the savings shrink, sometimes to zero or below if the fee outweighs the partial benefit.

How to read the secondary outputs

The result panel breaks the comparison into its components: the transfer fee, the total interest paid under each scenario, the number of months each scenario takes to clear the balance, whether the transfer cleared within the promo period, and the total of fee plus interest on the transfer side. The break-even-months figure shows how many months of avoided interest at the current rate would be needed to recoup the fee — useful for cases where the savings figure is small and it helps to see the payback time.

Where the simulation simplifies

The calculation assumes a steady monthly payment, no missed payments, no new spending on either card during the comparison, and a revert rate equal to the original card's rate after the promo ends. Real cards may apply a different revert rate, may charge minimum-payment fees, or may apply payments to balances in a different order. The result should be read as a clean comparison of the two scenarios under steady conditions, not a forecast of any specific account's behaviour.

Where to look next

For a balance that is being paid down on the current card without a transfer, the credit card minimum trap visualiser shows what happens when only minimum payments are made. The debt consolidation break-even calculator runs a similar comparison for unsecured loans rather than card transfers.