Deferred Interest Calculator
What a "no interest if paid in full" promo really costs if you miss it — the interest charged back to day one, and the reduced-APR plan that's often cheaper.
Interest charged retroactively when the promo ends
$150.00/month isn't enough. You'd still owe $1,200.00 when the promo ends — and because any remaining balance triggers it, the card adds $717.53 of interest calculated all the way back to the purchase date.
To pay nothing at all, you'd need $250.00/month — the purchase divided by the promo months.
What each path actually costs
| Option | Monthly | Interest | Total |
|---|---|---|---|
| Promo, paid in timeneeds $250.00/mo | $250.00 | $0.00 | $3,000.00 |
| Promo, missedat your $150.00/mo | $150.00 | $1,194.94 | $4,194.94 |
| 24 months at 17.9%fixed payments, no deferred interest | $149.63 | $591.06 | $3,591.06 |
| 36 months at 18.9%fixed payments, no deferred interest | $109.82 | $953.39 | $3,953.39 |
| 48 months at 19.9%fixed payments, no deferred interest | $91.13 | $1,374.30 | $4,374.30 |
Worth knowing before you sign: if you can't clear the promo in time, a reduced-APR instalment plan costs less than the retroactive interest — and it carries no deferred-interest trap at all. Ask the provider whether the purchase qualifies for one.
How the retroactive charge is built
- Purchase
- $3,000.00
- Paid over 12 months
- $1,800.00
- Balance when the promo ends
- $1,200.00
= interest accrued each month on the balance carried, at 32.99% ÷ 12
Monthly approximation — real cards accrue daily. Published terms checked 2026-07-14
How to use
- Enter the purchase, the promo length you were offered, and the payment you realistically plan to make each month.
- Read the headline: it's the interest charged retroactively if any balance is left when the promo ends — and it's calculated back to the purchase date, not from the end of the promo.
- Compare the paths. If you can't clear the promo in time, check whether a reduced-APR instalment plan costs less — it usually does, and it carries no deferred-interest trap.
How it works
The offer at the dental counter says "no interest if paid in full in 12 months." It sounds like a 0% loan. It isn't.
Interest is accruing from the day of the purchase at the card's standard rate — published at 32.99% — and the promise is only that it will be waived if you clear the entire balance in time. Miss the deadline by one payment, or by five dollars, and all of that accrued interest is charged at once, calculated back to day one. This calculator runs that accrual month by month at your actual planned payment, so the number arrives before the statement does.
It also does something the offer sheet doesn't: it compares the promo against the reduced-APR instalment plans the same card publishes for larger purchases. Those charge ordinary interest — but no retroactive lump. If you can't clear the promo in time, the "interest-bearing" option is very often the cheaper one, and almost nobody is told that at the counter.
All calculation happens in your browser. Your numbers never leave your device.
Frequently asked questions
What is deferred interest?
A "no interest if paid in full" promotion where interest quietly accrues from the purchase date at the card's standard APR — often around 33% — but is waived if you clear the whole balance before the promo ends. Clear it in time and you pay nothing. Leave any balance at all and every cent of that accrued interest is added to your account at once, calculated from day one.
Is CareCredit really 0% interest?
Its promotional financing is deferred interest, not 0% APR — and the difference only shows up if you miss. Under a true 0% intro APR, no interest accrues, so falling short simply means you start paying interest from that point on what's left. Under deferred interest, the interest was accruing the whole time; missing the deadline makes all of it payable retroactively. CareCredit publishes this plainly; people still get caught, because the two offers sound identical.
What happens if I'm one payment short?
The same thing that happens if you're a thousand dollars short. The trigger is any remaining balance, not how large it is — being $5 short at the deadline can cost you hundreds. That's why the calculator shows the payment that clears the balance exactly, and why leaving yourself margin matters more here than on almost any other kind of credit.
Deferred interest vs a 0% APR card — which is better?
A genuine 0% intro APR card is strictly safer, because there is no accrued interest waiting behind the offer. Deferred interest is only equivalent if you are certain you'll clear it in time. Use this calculator to see the size of the downside before deciding how confident you actually are.
Is the reduced-APR plan better than the promo?
If you can clear the promo in time, no — nothing beats paying zero interest. If you can't, then usually yes: a reduced-APR instalment plan (published at 17.9–19.9% over 24–48 months on larger purchases) charges interest, but a predictable amount, with no retroactive lump. Our comparison shows both so you can see which loses you less money.
What if I can't pay it off at all?
The calculator flags it: if your payment is smaller than the monthly interest on the post-promo balance, the debt never clears and simply grows. Before that happens, ask the provider about a reduced-APR plan, ask about a payment plan directly with the practice, and — for medical and dental care — ask whether you qualify for financial assistance. Those conversations are easier before you're behind than after.
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Before you decide
This tool is an educational estimate, not financial advice. It is not affiliated with, endorsed by, or connected to CareCredit or Synchrony Bank — that name appears only to identify the kind of financing being modelled. Interest here is approximated monthly while real cards accrue daily, and promotional terms, APRs and minimums change: your own cardholder agreement is what controls.