Deferred interest payoff calculator
Two products advertise the same 0% headline and behave nothing alike the moment you fall short. Find the payment that clears your promo in time, and see exactly what falling short costs under each one.
Worked example — Payment that clears $3,600 before month 18: $200.00. $3,600 promo balance, 18 months, 29.99% regular APR if unpaid
Price your own promotional balance
Enter the balance, the length of the promo, and the regular APR printed on the offer. This runs your planned payment through both products at once: a true 0% APR promo, where only the leftover balance starts accruing interest if you fall short, and deferred interest, where falling short at all charges interest on the whole balance back to day one.
$3,600, deferred interest, paying $180: A same-as-cash promo. $180 a month falls $20 short of the $200 needed to clear it, and every month of interest gets charged retroactively.
Advanced options 1
Assumes the disclosed regular APR applies from day one of a deferred-interest promo, and that your payment stays the same after the promo unless you set a different one under advanced options. Every month past the promo is a projection, not a statement you have seen.
The payment that clears a promo before it expires
$200.00 a month clears a $3,600 balance before an 18-month promo expires, paid in 18 equal instalments with nothing left over. That figure is the balance divided by the number of months, rounded up to the cent, because rounding to the nearest cent or down can leave a few cents outstanding on the final payment, which is enough to trigger a retroactive charge under a deferred-interest promo.
The same arithmetic at other common promo lengths, on the same $3,600 balance:
| Promo length | Required payment |
|---|---|
| 6 months | $600.00 |
| 12 months | $300.00 |
| 18 months | $200.00 |
| 24 months | $150.00 |
| 36 months | $100.00 |
True 0% APR vs deferred interest, same balance
At $180 a month against the $200.00 required, $3,600 still owes $360.00 when the 18-month promo ends. What happens to that $360.00 next depends entirely on which product it was.
| Product | Charged at month 19 | Total interest to pay it off | Paid off by |
|---|---|---|---|
| True 0% APR | $0.00 | $14.06 | month 21 |
| Deferred interest | $931.19 | $1,052.98 | month 26 |
Same balance, same shortfall, same regular APR. Deferred interest costs 75 times what true 0% APR costs on this shortfall, because it charges interest on the whole 18-month balance path, back to the first payment, and not just on the $360.00 that is actually left.
Are you charged interest if you do not pay off the promo balance
Yes, but which interest and how much depends on the offer's wording, not just its length. A card that advertises "0% intro APR" only starts charging on whatever is left, from the day the promo ends. A card that advertises "no interest if paid in full," "deferred interest," or "same as cash" instead charges interest retroactively, back to the purchase date, on the entire original balance the moment the ending balance is not exactly zero, and it is charged all at once rather than spread out.
On the default scenario here, falling $20.00 a month short leaves $360.00 outstanding at month 18. A true 0% APR card would charge $14.06 in total to pay that off. A deferred-interest card charges $931.19 the instant the promo ends, before a single extra dollar of ordinary interest is even added.
What the retroactive charge costs if you finish short
Paying $197.22 a month instead of the $200.00 required leaves $50.04 outstanding when the promo ends, about $50 short of clearing it. Under true 0% APR that costs $1.25 in total, ordinary interest on a small leftover balance. Under deferred interest it costs $865.34, charged the moment the promo ends, because the charge is not proportional to how short you finished. It is the interest the whole balance would have earned the card issuer with no promotion at all.
The position here is not that deferred interest is a scam: the terms are disclosed, by law, on the statement and in the advertising. It is that "0%" is doing different work in each offer, and the only way to know which one you have is to read the word next to it. "Interest is waived" and "0% intro APR" behave the way most people assume 0% behaves. "No interest if paid in full" and "deferred interest" do not, and the gap between them is the number above, not a rounding error.
Where the deferred-interest mechanism comes from
No dollar figure on this page is sourced from anywhere but your own inputs: the balance, the promo length, the payment, and the regular APR are all numbers you supply, and every result is arithmetic on them. What is sourced is the mechanism itself, because it is the part a reader cannot verify by doing the math alone.
- CFPB: How to understand special promotional financing offers on credit cards Checked 8 August 2026. States the distinction this page models: "Deferred interest means that if you do not pay off the entire balance of the promotional purchase you've made on your card, then interest going back to the date of the purchase will be added on top of the remaining balance."
- Regulation Z, 12 CFR 1026.7(b)(14) Checked 8 August 2026. Requires the periodic statement to disclose the date by which a deferred-interest balance must be paid in full to avoid finance charges, on the front of every statement during the deferred-interest period.
- Regulation Z, 12 CFR 1026.16(h) Checked 8 August 2026. Sets the advertising-disclosure duty for deferred-interest terms: the required disclosures must be equally prominent to the promotional claim itself.
Your own offer's terms govern, not this page. Read the box on your statement or the fine print on the offer for the exact deadline and the exact rate that applies if you miss it, since issuers vary both.
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