Balance Transfer Calculator
Compare transferring against staying put, including what is left when the promotion ends — and why the transfer fee is rarely what decides it.
Interest is compounded monthly at the annual rate divided by twelve, the fee is charged once on the whole balance at the start, and the payment is assumed constant. Real cards differ in how they apply payments across promotional and standard balances. Nothing is uploaded.
The payment decides this, not the fee
On $8,000 escaping 22.9% for 18 months at 0%, transferring saves $1,892 at $400 a month. But it does not clear inside the promotional window — when the promotion ends there is still $1,040 owing, and that reverts to 24.9%: higher than the rate that was escaped. At $ 200 a month it ends the window still owing $4,640.
| Monthly payment | Clears in the window? | Still owing when it ends | Months to clear | Saved against staying |
|---|---|---|---|---|
| $150 | no | $5,540 | never | — |
| $200 | no | $4,640 | 50 | $5,253 |
| $300 | no | $2,840 | 29 | $2,690 |
| $400 | no | $1,040 | 21 | $1,892 |
| $500 | yes | $0 | 17 | $1,397 |
The bottom row never clears at all: $150 a month is less than the first month's interest on the balance, so it grows faster than it is repaid and no payment schedule ever ends. There is no saving to quote for it — differencing two balances that both run away would have produced a number in the millions, which reads as a spectacular deal and means nothing.
Dividing the balance by the months underpays
The obvious plan is $8,000 over 18 months, or $444.44 a month. That falls short, because a 3% fee adds $240 to the balance on day one — the window is spent paying down $8,240, not $8,000. The payment that actually clears it is $457.78, and the difference of $13.33 a month is precisely the fee spread across the window. Pay the round number instead and you finish the promotion owing almost exactly the fee you forgot to count.
Why the fee is the wrong thing to shop on
Offers are marketed on 3% against 5%, but that is not where the money is. On this balance and rate gap the transfer still comes out ahead at a fee of 20% — far past anything any card charges. The fee is a one-off charge; the rate gap compounds every month for 18 months, and over that stretch it is much the larger number.
That is not a universal rule, and the calculator above will tell you when it stops holding. Narrow the rate gap — a balance at 6% moving to a 6% revert rate — and a break-even fee appears, because there is barely any interest being saved for the fee to be worth paying. Remove the gap entirely and no fee at all is worth paying. The three outcomes are genuinely different: not worth it, worth it up to some fee, and worth it at any fee you will ever be offered. Which one you are in depends on the gap between what you are paying now and what the promotion charges, and almost not at all on the headline percentage in the advertisement.
How to use
- Enter the balance, your current rate and what you pay each month.
- Add the promotional rate, its length, the fee and the revert rate.
- Compare the total cost of transferring against staying.
- Check the payment needed to clear it inside the promotion.
Frequently asked questions
Is a balance transfer worth it?
Usually, if there is a real gap between your current rate and the promotional one — but the calculator will tell you when it is not. On an $8,000 balance escaping 22.9% for eighteen months at 0%, transferring still wins even at a fee of twenty per cent, far past anything any card charges. Narrow the rate gap to a point or two and a break-even fee appears very quickly.
How is the transfer fee charged?
Once, up front, on the whole balance — not on the part that benefits. A three per cent fee on $8,000 adds $240 to what you owe on day one, so the promotional window is spent paying down $8,240 rather than $8,000.
What payment clears the balance inside the promotion?
More than the balance divided by the months, because the fee joined the balance. For $8,000 over eighteen months the obvious plan is $444.44 a month, and it falls short by $13.34 — leaving you owing almost exactly the fee you forgot to count when the promotion ends. The figure that actually works is $457.78.
What happens if I do not clear it in time?
Whatever is left starts accruing at the revert rate, which is frequently higher than the rate you escaped. At $400 a month our example ends the window still owing $1,040 at 24.9% — against the 22.9% it left. The transfer still saved money overall, but interest-free is not what happened.
Should I compare offers on the fee?
Rarely. The fee is a one-off charge; the rate gap compounds every month for the length of the promotion, and over that stretch it is much the larger number. Cutting a fee from five per cent to three changes the saving here by well under a sixth. The length of the promotion and the size of the rate gap matter far more.
Why does one payment show no saving at all?
Because it never repays the balance. A payment below the first month’s interest lets the balance grow faster than it shrinks, so there is no payoff date on either side to compare. Quoting a saving there would mean differencing two runaway totals, which produces a number in the millions and means nothing.
How is the interest worked out?
Compounded monthly at the annual rate divided by twelve, with the fee charged once at the start and the payment held constant. Real cards differ in how they apply payments across promotional and standard balances, so treat this as the shape of the answer rather than a statement of your exact account.
Does this send anything anywhere?
No. Every figure is computed in your browser, and nothing is uploaded or stored.
🔒 This tool runs entirely in your browser. Nothing you enter is uploaded, logged, or stored.