The trade-off in one sentence
The economics of a balance transfer are a straightforward trade: the fee is a certain, upfront cost, while the benefit is the interest that would otherwise have accrued at the old card's APR. The fee is added to the transferred balance and is due regardless of what happens afterward; the interest saved depends on the balance, the old APR, the length of the 0% window, and critically, how fast the balance is paid down during that window.
- Transfer fee = balance × (fee% ÷ 100)
- Monthly interest = balance × (APR ÷ 100 ÷ 12), applied at 0% during intro months in the transfer scenario
- Interest avoided = interest without transfer − interest with transfer
- Net savings = interest avoided − transfer fee
Worked example
Transferring a $5,000 balance at 22% APR with a 3% fee ($150) to a 15-month 0% card, paying $350 a month, clears the debt entirely within the 0% window and saves about $701 net of the fee versus staying at the current 22% APR. The saving is entirely a function of paying the balance down fast enough to actually benefit from the interest-free window rather than carrying a residual balance into the card's regular APR.
When it doesn't pay off
A small balance that would be paid off in a few months anyway at the original APR may save little or nothing after the fee, since there's little interest to avoid in the first place. Paying only minimums during the 0% window leaves a large residual balance exposed to the regular APR once the promotion ends, which erodes or eliminates the benefit. And if the entered monthly payment does not even exceed the current card's monthly interest charge — balance × APR ÷ 12 — the balance can never amortize at all, a condition that makes any transfer-vs-stay comparison moot until the payment is raised.
| Result | What it means |
|---|---|
| Net savings clearly positive | Interest avoided exceeds the fee — the transfer beats staying put at this payment level |
| Net savings near zero or negative | The fee eats most or all of the interest benefit — typical with a small balance, a short intro window, or a payment that clears the debt quickly anyway |
| Payment doesn't cover monthly interest | The balance never falls under either path; a higher payment is needed before any comparison is meaningful |
What to watch for beyond the arithmetic
New purchases on a transfer card typically accrue interest at the regular purchase APR immediately, which can complicate payment allocation — the CFPB advises avoiding new spending on a card carrying a promotional transferred balance. Missing a payment often cancels the promotional rate outright, reverting the balance to a penalty or regular APR. And standard balance-transfer promotions are not deferred-interest deals — interest is not charged retroactively — but 'no interest if paid in full' financing promotions common in store cards do charge interest retroactively, so confirming which type of promotion applies matters before transferring.
よくある質問
Is a balance transfer worth it?
It's worth it when the interest avoided during the 0% window exceeds the transfer fee — favoring larger balances, higher current APRs, longer promotional periods, and aggressive payments. In a worked example, $5,000 at 22% APR with a 3% fee, 15 months at 0%, and $350 monthly payments saves about $701 after the $150 fee.
How much is a typical balance transfer fee?
Most balance transfer offers charge 3% to 5% of the amount transferred, added to the new balance rather than paid separately. A $5,000 transfer at 3% costs $150, so the new card starts with a $5,150 balance.
What happens when the 0% introductory period ends?
Any balance remaining begins accruing interest at the card's regular APR from that point forward. Standard balance-transfer promotions don't charge interest retroactively, but some store-card 'no interest if paid in full' promotions do — checking which type applies matters.
Can a balance transfer ever cost more than it saves?
Yes — on a small balance that would have been paid off quickly anyway, or with only minimum payments made during the promotional window leaving a large balance exposed to the regular APR afterward, the fee can exceed or erode the interest saved.
参考文献
- Consumer Financial Protection Bureau (CFPB) — What is a balance transfer and how does a balance transfer fee work? https://www.consumerfinance.gov/
- Consumer Financial Protection Bureau (CFPB) — What is a deferred interest / promotional APR offer? https://www.consumerfinance.gov/
- Federal Reserve Board — Regulation Z (Truth in Lending), payment allocation rules. https://www.federalreserve.gov/