The True Cost of a No-Interest Promo Period

A no-interest promotion is not free credit, and its cost depends on which of two designs it uses. With a true 0% intro APR, interest begins only on whatever balance is left when the promotion ends. With deferred interest, interest has been accruing in the background since the purchase date, and any unpaid balance at the deadline triggers all of it at once.

Key takeaways

"0% intro APR for 12 months" and "no interest if paid in full in 12 months" are different contracts; the "if" signals deferred interest, according to the Consumer Financial Protection Bureau (CFPB).
In the illustrative example below, leaving $240 of a $2,400 purchase unpaid costs $6.87 in later interest under a true 0% offer and $380.56 in back-charged interest under a deferred-interest offer.
Balance transfers usually carry a fee. In the second example, a 3% or 5% fee ($150 or $250) is still far below the $764.38 of interest on the same $5,000 at 22% repaid over the same 15 months; the saving shrinks if part of the balance is still owed when the promotion ends.
Federal card rules require a promotional rate to last at least six months and direct extra payments to a deferred-interest balance in the last two billing cycles, but they leave the post-promotion rate to the card agreement.

Three kinds of "no interest" offers

The same phrase covers products with different mechanics. The table sets them side by side; the sections after it explain the two that cause most of the surprises.

Type	How it is usually advertised	If a balance remains at the end	Where it is common
True 0% intro APR	"0% intro APR for 12 months"	Interest applies only to the remaining balance, from the end date onward	Credit cards, on purchases or balance transfers
Deferred interest	"No interest if paid in full in 12 months"	All interest accrued since the purchase date is added	Store cards and medical or dental financing cards
Pay-in-four BNPL	Four interest-free installments	No promotional window; the risk is missed installments, not a lump of back interest	Retail checkout, typically for purchases of about $50 to $1,000

The first two rows follow the CFPB's 2017 explanation of promotional financing offers. Deferred interest is typically offered on store credit cards for appliances, furniture and medical or dental services, per the CFPB's June 2017 announcement. The BNPL row follows the CFPB's September 2022 market report, which describes four even payments, the first at checkout and the rest every two weeks over six weeks, and notes risks such as required autopay.

True 0% APR vs deferred interest

APR (annual percentage rate) is the yearly cost of borrowing expressed as a rate. During a true 0% intro period it is zero. When the period ends, the card's regular rate, sometimes called the go-to rate, applies to whatever is still owed, and only from that day.

Deferred interest keeps the regular rate running behind the scenes. Nothing is billed during the promotion, but if any part of the promotional balance remains at the end, the issuer adds the interest accrued back to the purchase date. The CFPB's example uses a $400 television with $100 unpaid after 12 months at a 25% rate: $65 of deferred interest is charged under that design, so $165 is owed when the promotion ends, against $100 under a true 0% offer. The unpaid amount is only a quarter of the purchase, yet the interest charge is computed on the whole purchase's declining balance.

The pattern shows up in health care too. A May 2023 CFPB release reported that patients paid about $1 billion in deferred interest on medical credit cards and loans from 2018 to 2020, on almost $23 billion of health care expenses. The same release cites 26.99% for medical credit cards, "according to available public information". The full report adds that about 20% of healthcare purchases on deferred-interest cards or loans ended with interest assessed (around 34% for borrowers with credit scores below 619), and that in 2020 the deferred interest charged on the purchases that were assessed interest came to about 23% of their original purchase amounts.

Worked example: a $2,400 purchase

Illustrative example. A $2,400 purchase on a 12-month promotion, with a 26.99% go-to rate. The cardholder pays $180 a month, $20 short of the $200 needed to clear it (2,400 ÷ 12).

The deferred-interest figure uses a monthly approximation rather than a card's exact daily method:

monthly interest = balance carried × APR ÷ 12
deferred interest = sum of the 12 monthly amounts, each on the balance before that month's payment

Here the balance is the amount still owed that month, APR is 0.2699, payments land at month end (so the balance is level within each month), and interest does not compound during the promotion. The same convention gives $65.62 for the CFPB's $400 television, close to the CFPB's $65. A real issuer works from average daily balances and statement dates, so its figure will differ by some dollars.

Scenario	Unpaid at month 12	Interest charged	Result
True 0%, $200 a month	$0	$0	Cleared on time
True 0%, $180 a month	$240	$5.40 in month 13; $6.87 in total if $180 payments continue	Cleared in month 14 with a final payment of $66.87
Deferred interest, $200 a month	$0	$0 if paid in full before the deadline	Cleared on time
Deferred interest, $180 a month	$240	$380.56 back-charged, then $33.08 more over four further payments	Balance jumps to $620.56 at the end of the promotion

The gap is large because of what each design charges for. Under a true 0% offer, the $240 left over costs about 2.9% of itself in interest by the time it is repaid. Under deferred interest, the $240 shortfall releases $380.56 of interest, about 1.6 times the unpaid balance, because the interest was calculated on the declining balance of the full $2,400 for all 12 months. The back-charge exceeds $240 even though only 10% of the purchase was unpaid.

To test other prices, terms or rates on a fixed repayment schedule, use the loan calculator.

What a balance transfer costs

A balance transfer moves existing card debt to a new card, usually to use that card's 0% period. The CFPB states that a card company may charge a balance transfer fee on a zero percent offer, and its key terms page describes the fee as usually a percentage of the amount transferred or a fixed amount, whichever is more.

Published issuer terms show the spread. One issuer's balance transfer page lists 3% of each transfer or $5, whichever is greater, with a 12-month 0% period and a 90-day window to submit the transfer. Another issuer's pricing and terms, accurate as of March 24, 2026, list 5% or $5, whichever is greater. These are examples of terms, not recommendations, and offers change. Across the market, the CFPB's October 2023 credit card market report put the average fee at 2.8% of the amount transferred in 2022, down from 3.0% in 2020.

Illustrative example. Moving $5,000 to a 15-month 0% offer, with the fee added to the balance and repaid in 15 equal payments, compared with keeping the $5,000 at 22% APR and also repaying in 15 equal payments. The 22% figure is a round number near the Federal Reserve's 22.15% average at commercial banks for credit card accounts assessed interest in the second quarter of 2026 (all accounts: 20.94%), from the G.19 consumer credit release of October 7, 2026.

Option	Fee or interest	Monthly payment	Total paid
Transfer, 3% fee	$150.00 fee	$343.33	$5,150.00
Transfer, 5% fee	$250.00 fee	$350.00	$5,250.00
Stay at 22% APR	$764.38 interest	$384.29	$5,764.38

The transfer saves about $614 at a 3% fee and about $514 at 5%, and it also lowers the monthly payment. Those figures assume the balance is cleared within the 15 months; any amount left over starts accruing at the card's go-to rate, which eats into the saving, and some offers require the transfer within a set window after opening the account.

Rules that shape these offers

These federal rules apply to credit card accounts under open-end plans that are not secured by a home, as written in Regulation Z. They set floors for promotions but leave the post-promotion rate to the card agreement. They do not reach installment loans, including the medical financing loans mentioned above, because those are not credit card accounts.

Minimum length. Under 12 CFR 1026.55, a card issuer may raise a rate at the end of a specified period of six months or longer, provided it disclosed in writing beforehand the length of the period and the rate that will apply afterward.
Late payments. The same section allows an increase if the required minimum payment is not received within 60 days after the due date. The issuer must send written notice at least 45 days before the increase takes effect (12 CFR 1026.9(g)), state the reason, and reduce the rate again after six consecutive on-time minimum payments, starting with the first payment due after the increase. That reduction covers transactions made before, or within 14 days after, the notice.
Payment allocation. Under 12 CFR 1026.53, payments above the minimum normally go to the highest-APR balance first. For a balance under a deferred-interest or similar program, the excess must go first to that balance during the two billing cycles before the period expires, or the issuer may follow the cardholder's request instead.

Penalty rates sit in the card agreement, not in the federal rule. One large issuer's terms, accurate as of March 24, 2026, list a penalty APR of up to 29.99%, which may apply if a minimum payment is missed by its due date or a payment is returned, and say it could remain in effect indefinitely. The federal limits above still govern how far that reaches: on existing balances an increase needs the 60-day delinquency and ends after six on-time payments, and outside that exception a higher rate generally applies only to new transactions, after 45 days' notice and not in the account's first year. Across large issuers, the CFPB's 2023 market report found no accounts with APRs at or above 36% in a representative sample of its data, and described rate increases under the 60-day exception as fairly uncommon.

Whether card-style rules reach buy now, pay later is a separate question. A 2024 CFPB interpretive rule would have applied card-style Regulation Z provisions to certain BNPL accounts, but the CFPB's BNPL page states that the bureau withdrew it on May 12, 2025, confirmed by the withdrawal notice in the Federal Register. The provider's own terms for late fees and autopay are the first thing to read.

Frequently asked questions

Can the promotional rate end early if I pay late?

The CFPB says an introductory rate must last at least six months unless the cardholder is more than 60 days late on a payment. A variable introductory rate can still change during that period if its index, such as the prime rate, changes. The card agreement also sets any penalty rate that follows a missed payment.

Do extra payments reduce a deferred-interest balance first?

Not automatically. Outside the last two billing cycles, extra payments normally go to the balance with the highest APR, so a deferred-interest balance can be left behind. The CFPB's advice is that a cardholder can ask the issuer to apply extra payments to the deferred-interest balance.

Is the minimum payment enough to clear a promotion?

The CFPB notes that the minimum payment is usually not enough to clear the balance before the promotion ends. Dividing the purchase by the number of months, as in the $200 figure above, gives a payment target. A payment of that size on a deferred-interest offer works only if the balance reaches zero before the deadline.

Does the issuer have to say what happens after the promotion?

For a promotional rate that a card issuer later increases, Regulation Z requires a written, clear disclosure before the period begins of its length and of the rate that will apply afterward. The post-promotion rate is therefore in the offer documents, and it is worth reading before accepting.

Does pay-in-four BNPL charge back interest if I miss a payment?

The CFPB's 2022 report describes pay-in-four loans as interest-free, so there is no deferred-interest back-charge in that structure. The risks it identifies are different: required autopay, data harvesting and overextension, and some providers charge late fees while others do not.

Before you accept an offer

Find the exact wording. "0% intro APR" means interest starts on the remaining balance only; "no interest if paid in full" means deferred interest.
Write down the end date and the go-to rate shown in the terms.
Divide the price by the number of months for a payment target, and if the offer is deferred interest, schedule the last payment to land before the final statement date.
For a balance transfer, add the fee to the balance and compare the total with the interest the same payments would cost at the current rate.
Keep other purchases on a different card. Extra payments go to the higher-rate purchases first, outside the last two billing cycles of a deferred-interest offer, and the CFPB's 2023 report notes that new purchases on a card carrying a transferred balance typically get no grace period.