FinBedrock Calculator
Store-Card Deferred Interest Calculator
By Nick Buinenko · Last reviewed: October 6, 2026
See the monthly payment that keeps a "no interest if paid in full" promo at $0 — and exactly how much deferred interest you'd owe if you miss the deadline by even a dollar.
“No interest if paid in full within 12 months” only works if the balance is actually gone by the deadline. Leave anything behind, even a single dollar, and the card charges all the interest that has been quietly building up since the day you bought the item. This calculator shows the monthly payment that keeps a deferred-interest promo at $0, and exactly what you’d owe if you miss.
Every number it shows comes from the same engine, run on your inputs: no estimates typed by hand, no sign-up, and nothing you enter is stored.
How to Use the Calculator
- Pick what you’re working out. “Planning a purchase” is for a promo you’re about to take. “Already have a promo balance” is for one you’re in the middle of: you’ll add how many months have passed and the promotional balance on your latest statement.
- Enter the purchase amount and the promo length. The length is the number in “no interest if paid in full within…”: 6, 12, 18, 24 months, or any other length your offer states.
- Enter the card’s standard purchase APR. That’s the rate deferred interest is charged at, not 0%. You can pick one of the store cards we review to fill in its highest purchase APR. Your own APR may be lower, so check your statement.
- Optionally, enter what you plan to pay each month. Leave it empty to see the payment you need. If you’re paying only the minimum from your statement, enter that amount and see where it leaves you.
The results update as you type. A month-by-month table underneath shows the balance and the interest building up each cycle.
What the Results Mean
- Pay at least this each month. The promotional balance divided evenly over the months left, rounded up to the cent. Pay this and nothing is left on the deadline, so the deferred interest is waived.
- The one-month-early figure. The same balance spread over one fewer month. It finishes a cycle early, which is cheap insurance against a payment that posts a day late or lands on the wrong balance.
- What’s at stake. All the interest that builds up on the promo along your payment path. It is never charged if you finish on time, and charged in full, at once, if you don’t.
- Short by $1. What the card would charge if you paid almost everything and missed by a single dollar. This is the line that shows why deferred interest is all-or-nothing.
- With daily accrual — up to. Card agreements typically calculate interest daily and compound it, which lands a little higher than our monthly figure. Treat this line as the top of the range.
Worked Examples
All three use a $2,000 purchase on a 12-month promo at a 30.14% APR, Bankrate’s reported average for retail cards as of September 15, 2025. That’s an illustrative rate, not any specific card’s.
Paying the required amount
At $166.67 a month, the balance hits zero by month 12 and the charge is $0. Along the way, $326.51 in deferred interest builds up in the background, which is what you would have owed if anything had been left. Paying $181.82 a month clears it one cycle early.
Paying $1,900 of the $2,000
Pay about $158.33 a month and $100 is left on the deadline. You aren’t charged interest on the $100. You’re charged everything that built up since the purchase: $340.33, on top of the $100 itself. With daily compounding the same plan comes to as much as $414.46. Miss by a single dollar instead, and the charge is still $326.65.
Paying only a $70 statement minimum
Some store cards set the promo minimum at 3.5% of the promotional balance. That’s $70 on the first statement of a $2,000 purchase. Pay a flat $70 a month and $1,160 is still owed on the deadline, so all $486.76 of deferred interest is charged at once. Pay nothing at all for the 12 months, and the charge is $602.80.
Deferred Interest vs. a True 0% APR
The two offers can look identical in an ad. They behave very differently on the deadline:
| Missed the deadline with $100 left | True 0% APR offer | Deferred-interest promo |
|---|---|---|
| Interest charged on the deadline | $0 | $340.33 |
| What happens next | Regular APR on the $100 from now on | Regular APR on the $100 plus the $340.33 |
With a true 0% intro APR nothing builds up during the promo. Our guide to 0% intro APR and balance transfers covers that side. With deferred interest, the interest was never gone, only postponed.
How the Math Works
Interest builds up each billing cycle on the promotional balance that is still unpaid, at the card’s standard purchase APR, and your payment is applied at the end of the cycle. That is the method the CFPB itself uses to explain deferred interest. The calculator reproduces the CFPB’s example: a $400 TV, $25 a month, a 25% APR and $100 left on the deadline gives $65.63 of deferred interest, against the CFPB’s own “$65”. The full method, its assumptions and the sources are under Methodology below.
In “Already have a promo balance” mode, the interest from the months that have already passed is an estimate, because the calculator doesn’t know your exact payment history. It assumes you paid the balance down evenly to today’s figure. Your statement has the real number.
How Not to Fall Into the Trap
- Divide, don’t trust the minimum. Take the promotional balance and divide it by the months left. On many plans the minimum due is not designed to clear the promo in time.
- Finish a month early. The one-month-early figure costs little and protects you from a slow or misapplied payment.
- Watch other balances on the same card. If you carry another balance, the issuer can apply anything above the minimum to that balance first, until the last two billing cycles of the promo.
- Check the payoff date on every statement. Issuers are required to print it.
For the full story of how these promos work, why store cards are where they live, and the CareCredit enforcement case that shows what goes wrong, read Deferred Interest Explained: The Store-Card Trap. Before opening a store card for a single purchase, see whether its rewards are worth the APR in Are Store Credit Cards Worth It? and compare the options in our best store credit cards roundup.
Methodology & sources
Model
The calculator follows the method in the issuers’ own card agreements and the CFPB’s explanation of deferred interest.
- What builds up. Interest accrues on the promotional balance that is still unpaid: the purchase amount minus your payments so far. It starts on the purchase date, at the card’s standard purchase APR.
- When it’s charged. Nothing is charged while the promo runs. If the promotional balance is paid in full by the deadline, all of it is waived. If any balance is left, all of it is charged at once and then accrues regular interest along with what’s left.
- Headline figure (monthly). Each billing cycle adds interest of APR ÷ 12 on the balance outstanding during that cycle, with no compounding, and your payment is applied at the end of the cycle. This reproduces the CFPB’s own example: $400, $25 a month, a 25% APR and $100 left on the deadline gives $65.63, against the CFPB’s “$65”.
- Upper bound (daily accrual). Synchrony’s and Comenity’s agreements calculate interest daily (APR ÷ 365) on each promotional balance and add each day’s interest to the next day’s balance. The “with daily accrual — up to” line uses that method over the promo’s days, with each payment posted no earlier than in the monthly model. It is therefore never below the headline figure.
Assumptions
- One promotional purchase and no other balances on the card. With other balances, payments above the minimum can go elsewhere first, except in the last two billing cycles before the promo ends (12 CFR 1026.53(b)(1)).
- The same payment every month, posted on time at the end of each cycle.
- No fees, no minimum interest charge, and no penalty APR. Interest after the deadline is not included.
- “Already have a promo balance” mode does not know your payment history. It assumes you paid the balance down evenly from the purchase amount to today’s balance, so the interest built up so far is an estimate.
- The required payment is the remaining promotional balance divided by the months left, rounded up to the cent. The one-month-early figure divides it by one month fewer.
- APRs filled in from the store-card list are the highest purchase APR in our review of that card. Your own APR may be lower.
Sources
- CFPB, “How to understand special promotional financing offers on credit cards” (June 8, 2017): the $400 example and the month-by-month method.
- Regulation Z, 12 CFR 1026.16(h): the definition of deferred interest (“finance charges, accrued on balances or transactions…”).
- Regulation Z, 12 CFR 1026.53: how payments are allocated, including the last-two-billing-cycles rule for deferred-interest balances.
- Synchrony Bank card agreements (CareCredit, Lowe’s, Amazon; CFPB credit card agreement database): a separate daily balance for each promotion, and interest imposed from the purchase date if the promotional balance isn’t paid in full.
- Comenity Capital Bank card agreements (Zales, Kay): “Interest accrues on plan balances from the transaction date. We do not impose that interest if you pay the balance in full by the end of the promotional period.”
- Bankrate, retail credit card survey (September 15, 2025): the 30.14% average retail-card APR used in our worked examples, as an illustration only.
Sources
- CFPB — How to understand special promotional financing offers on credit cards (Jun 8, 2017)
- 12 CFR 1026.16(h) — Deferred interest or similar offers (Regulation Z)
- 12 CFR 1026.53 — Allocation of payments (Regulation Z)
- Synchrony Bank — CareCredit Rewards Mastercard Account Agreement (CFPB agreement database)
- Comenity Capital Bank — Zales Credit Card Agreement
- Bankrate — Retail credit card interest rates survey (Sep 15, 2025)
Cite or link to this calculator
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Source: Store-Card Deferred Interest Calculator, FinBedrock — finbedrock.ai/calculators/store-card-deferred-interest/
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Frequently Asked Questions
How is deferred interest calculated?
Interest builds up every billing cycle on the part of the promotional balance that is still unpaid, at the card’s standard purchase APR, starting on the purchase date. It isn’t charged while the promo runs. If the balance is paid in full by the deadline, all of it is waived. If anything is left, the whole built-up amount is charged at once. That is the method the CFPB uses to explain deferred interest, and our calculator reproduces its example: a $400 purchase, $25 a month and a 25% APR leave $100 on the deadline and about $65 of deferred interest.
If I pay most of the balance, do I still owe interest on the whole purchase?
You don’t owe interest on the original amount for the full promo, but you do owe all the interest that built up on the balance while it was still unpaid, and that is far more than interest on what’s left. On a $2,000, 12-month promo at a 30.14% APR, paying $1,900 leaves $100 on the deadline and a $340.33 charge. Missing by a single dollar still costs $326.65. Paying nothing at all for the 12 months would cost $602.80.
Why doesn't paying the minimum keep me safe?
On most deferred-interest plans the minimum payment is sized to keep the account in good standing, not to clear the promo by the deadline. The issuers say so in their own agreements: Synchrony’s CareCredit agreement says the minimum payments “may or may not pay off the promo purchase before the end of the promo period.” Some store cards set the promo minimum at 3.5% of the promotional balance. That’s $70 on a $2,000 purchase, and paying a flat $70 a month on a 12-month promo at 30.14% leaves $1,160 on the deadline and a $486.76 charge. Enter your statement minimum in the calculator to see where it leaves you.
How are my payments applied if the card has other balances?
Federal rules (Regulation Z, 12 CFR 1026.53) let the issuer apply the minimum payment however it chooses. Anything you pay above the minimum normally goes to the balance with the highest APR first, and a deferred-interest balance counts as a 0% balance for that purpose. The exception is the last two billing cycles before the promo ends: then the extra must go to the deferred-interest balance first. Issuers may also apply it the way you ask. The calculator assumes the promo purchase is the only balance on the card, so if you carry other balances, pay extra early and ask the issuer to apply it to the promo.
Is the calculator's figure exactly what my card will charge?
It’s a close estimate, not your statement. The calculator builds up interest once per billing cycle at the APR you enter. Card agreements typically calculate interest daily and compound it, which lands somewhat higher, so the results also show a “with daily accrual — up to” figure as the top of the range. Billing-cycle lengths, payment dates, fees and other balances also move the real number. Your card agreement and statement are the final word.
Which APR should I enter?
The card’s standard purchase APR, the rate printed on your statement and in your card agreement, not the 0% of the promo. Deferred interest is charged at that standard rate. If you pick a store card from the list, the calculator fills in the highest purchase APR from our review of that card. Your own APR may be lower, so check your statement and edit the field.
Does the calculator save what I enter?
No. The numbers you type are sent to our server only to run the math and are not stored, and the calculator needs no sign-up or email.
This content is for informational and educational purposes only and does not constitute financial advice. Credit card terms and APRs change — always verify current details directly with the issuer before applying.