A balance transfer pays off when the interest you stop paying is bigger than the fee. The calculator shows both: the transfer fee, and your saving after the fee.
That saving rests on one big assumption. It assumes the whole balance would have sat at your old card's rate for every promo month.
Fee against interest: the whole sum
On $5,000 at a 3% fee, the transfer costs $150. At 22% for 18 months, the old card would charge $1,650 in simple interest. That leaves the $1,500 the calculator reports.
Avoided interest covers the fee quickly. At 3% and 22%, it takes about 1.6 months of avoided interest. A 5% fee needs about 2.7 months.
Check the offer for a floor, too. The Consumer Financial Protection Bureau (CFPB) says the fee is usually a percentage or a fixed amount. You pay whichever is more, and the calculator applies the percentage only.
The saving assumes you'd never pay it down
If you were going to pay the old card down anyway, the transfer avoids less interest. The saving shrinks with it.
An even paydown, where the balance falls by the same amount each month, is easy to model. Over N months, it costs the same interest as the full balance for (N + 1) ÷ 2 months:
| Without the transfer, you would have | Months entered | Net saving after the $150 fee |
|---|---|---|
| Left all $5,000 untouched for 18 months | 18.0 | $1,500 |
| Paid it down evenly over 18 months | 9.5 | $721 |
| Paid it down evenly over 12 months | 6.5 | $446 |
| Paid it down evenly over 6 months | 3.5 | $171 |
| Paid it down evenly over 2 months | 1.5 | −$13 |
Paid down over the same 18 months, the transfer saves about $721, less than half the headline. Clear it in two months, and the fee costs more than the interest it avoids.
Planning the payments themselves? The credit card payoff calculator shows the monthly payment and total interest for a chosen payoff term.
Longer promo or lower fee?
Promo months after the debt is gone are worth nothing. Say you'll clear the $5,000 evenly over 12 months. Every offer below covers that, so you enter 6.5 months for each, and only the fee differs:
| Offer | Fee | Months entered | Net saving |
|---|---|---|---|
| 0% for 12 months, 3% fee | $150 | 6.5 | $446 |
| 0% for 18 months, 4% fee | $200 | 6.5 | $396 |
| 0% for 21 months, 5% fee | $250 | 6.5 | $346 |
Here each point of fee costs $50, and the extra promo months buy you nothing. A longer offer earns its higher fee only if you'd need the time. Then compare that fee with what the shorter offer's leftover balance would cost once its promo ends.
Where to find the APR to enter
Use the rate your old card charges on the balance you're moving. According to the CFPB, your statement must show each category with a different APR and the balance in each.
No statement handy? The Federal Reserve's G.19 release of September 8, 2026 gives a benchmark. At commercial banks, card accounts charged interest averaged 22.15% in the April–June 2026 quarter. The stated APR across all accounts averaged 20.94%.
So the calculator's 22% default sits close to the first figure. The credit card interest calculator shows what your own rate costs in a year.
Keep new purchases off the card
A 0% transfer doesn't make the new card interest-free. According to the CFPB, most cards charge interest on purchases from the transaction date if you carry a balance. That holds even when the balance you carry is a 0% transfer.
Payments then favor the purchases. Anything you pay above the minimum generally goes to the balance with the highest rate first. How the minimum itself is applied is generally up to the issuer. So the transferred balance shrinks more slowly while its promo clock keeps running.
When the 0% ends, or a payment slips
The CFPB notes that the promotional rate on most balance transfers lasts a limited time. After it ends, your rate may rise, and so may your payment.
To finish in time, divide what you owe by the promo months. With a $150 fee charged to the card, that's $5,150 ÷ 18 = $286.11 a month.
Paying more than 60 days late lets the issuer raise the rate on all balances, including the transferred one. Moving only part of your debt? The debt avalanche calculator plans the payoff of the remaining cards, highest rate first.
Zero percent is not deferred interest
The calculator assumes a true 0% rate on the transferred balance. Some promotions work differently: no interest if you pay in full by a deadline.
Miss that deadline and you're charged interest. The CFPB says it's usually worked out on your balance in each month since the purchase. Being more than 60 days late can also cost you the deferred-interest period.
The saving shown here holds for a real 0% rate, or for a deferred deal you clear in time.
Sources
- CFPB, Credit cards key terms: balance transfer (page last modified December 28, 2022)
- CFPB, Do I pay interest on new purchases after I get a zero or low rate balance transfer? (reviewed January 22, 2024)
- CFPB, My bill shows different APRs: how does that work? (reviewed January 22, 2024)
- CFPB, No interest if paid in full within 12 months: how does this work? (reviewed January 22, 2024)
- Federal Reserve, G.19 Consumer Credit, terms of credit (September 8, 2026)