Deferred interest calculator

Retroactive interest charged when the window closesworked example

$472.34

Balance at month 12 (before the charge): $600.00
Balance after the retroactive charge: $1,072.34
Monthly that would have cleared the window: $200.00Purchase / promo months, rounded up to the cent
Final payoff at $150.00/month: April 1, 2028
Total interest at the planned payment: $596.07

At $150.00/month, $600.00 of the $2,400 purchase remains when the 12-month window closes. Interest accrued silently from day one at 29.99% the whole time, and because a balance remained, all $472.34 of it landed at once — the balance jumps to $1,072.34. Paying $200.00/month instead would have cleared it in time and cost $0.00; this scenario costs $596.07 in interest and finishes in 1 yr 8 mo.

Purchase amount ($)This models "no interest IF paid in full" (deferred-interest) offers — not true 0% intro APRs.Deferred APR (%)The rate accruing behind the promo — typically 26.99–31.99% on store cards.Promo window (months)The "if paid in full within N months" figure in the offer.Planned monthly payment ($)Store minimums are usually far below the amount that clears the window.

Model a "no interest if paid in full" store-card promo honestly: interest accrues silently from day one, and if any balance remains when the window closes, all of it is charged at once. See the payment that truly clears it in time, and what the bill becomes if you miss.

How to use this calculator

1
Confirm which kind of offer you actually have
A true 0% offer says "0% intro APR." A deferred-interest offer says "no interest IF paid in full." Only the second one accrues interest silently the whole time. The wording is on the promotional terms and it is the difference between a good deal and a trap.
2
Enter the purchase and the card's deferred APR
The deferred APR is usually the card's standard rate, commonly around 27% to 32% on store cards. It is what the accrued interest is computed at — you are not being charged it monthly, but it is accumulating in the background from the purchase date.
3
Set the window exactly as the offer states it
Windows are usually 6, 12, 18 or 24 months from the purchase date, not from your first statement. If the offer says 12 months and you bought in November, the deadline is the following November — a date worth putting in a calendar the same day.
4
Compare your planned payment to the required one
The required figure clears the purchase inside the window. Store card minimums are typically far below it, which is precisely how people arrive at the deadline still owing something. If your planned payment is lower, the tool shows what that costs.
5
Look at the retroactive charge before deciding
If a balance remains when the window closes, all the interest accrued since day one lands at once. Seeing that number for your own purchase is usually what makes the required payment feel affordable by comparison.

Deferred-interest retroactive charge — interest accrues silently from day one; if any balance remains at window close, ALL accrued interest is charged at once. Verified 2026-07-31 against CFPB — No interest if paid in full within 12 months: how does this work? (accrual is modelled monthly on the declining balance; issuers compute it daily on average daily balance)

Everything you type here is computed in your browser. Nothing you enter is stored on a server, sent anywhere, or shared — there is no account, and your balances never leave your device.

Frequently asked questions

How is deferred interest different from a real 0% intro APR?

A true 0% offer says "0% intro APR"; a deferred-interest offer says "no interest IF paid in full." Under deferred interest, the CFPB explains, interest accrues from the purchase date the whole time — and if any balance remains when the window closes, all of that accrued interest is added to your bill at once. The word "if" is the entire trap.

What payment actually clears the promo in time?

The purchase divided by the number of promo months, rounded up to the next cent. Store minimum payments are usually far below this figure, which is how people arrive at month 12 with a balance and a retroactive charge. This calculator shows both numbers side by side.

What happens if I still owe $50 on the last day?

You are charged the accrued interest on the whole declining balance since day one — often several hundred dollars against that $50. The calculator shows the exact retroactive amount for your numbers, because seeing it is what makes the required payment feel worth making.

When do these promos actually make sense?

When you have done this arithmetic and set up an automatic payment at or above the clear-by-date figure. The promo then genuinely costs nothing. The failure mode is treating the store's minimum payment as the plan — the tool exists so the real plan is one screen away from the checkout counter.

Why does the calculator warn me about dates in January?

Deferred-interest promos cluster around holiday purchases, so windows opened in November and December close in deep winter the following year. If you save a payoff plan here, the site can warn you when a promo end date falls before your plan clears that balance.

How exact is the retroactive figure?

Accrual is modelled monthly on the declining balance under the convention this site states everywhere; issuers compute it daily on the average daily balance, so your actual charge can differ somewhat. The order of magnitude — and the fact that it lands all at once — is the part that matters, and that part is exact.

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