A "5% flat rate" almost never means what it sounds like. Enter your loan amount, flat rate, and APR offer to see the true equivalent APR — and which option actually costs less in real dollars.
~9.1% APR
5% flat rate (5 yrs) ≈
Full amount vs. balance
Charged on
Auto loans, Murabaha deals
Common in
Set the principal — the amount you're actually financing, before any interest, markup, or charges are added.
Input the headline flat rate you've been quoted — common for auto loans, personal loans, and some Murabaha financing.
Input any competing APR offer you want to compare it against, or leave the default to see the flat rate's true equivalent.
See the effective APR of the flat rate instantly, plus total cost, monthly payment, and which option actually saves you money.
APR is charged on the remaining (reducing) balance each month — as you pay down principal, the rate applies to a smaller and smaller amount.
Flat rate is charged on the full original amount for the entire term, even in the final month when you've nearly paid it off. This is why a flat rate always costs more than its headline percentage suggests.
Imagine borrowing $20,000 for 5 years. Lender A offers "5% flat rate." Lender B offers "9% APR." At first glance, 5% sounds like the obviously better deal — it's almost half of 9%. But the two numbers are calculated using completely different methods, and comparing them directly is comparing apples to oranges.
A flat rate charges interest on the full original $20,000 for every single year of the 5-year term — even in year 5, when you've already repaid most of the principal. An APR loan charges interest only on the remaining balance each month, which shrinks steadily as you pay it down. The flat rate's 5% headline figure, once converted to a true reducing-balance equivalent, often lands close to or above the APR offer.
5% Flat Rate
9% APR
The "9% APR" offer — which sounds nearly double the "5% flat rate" — actually costs slightly less in total dollars. The headline percentages are not on the same scale.
Many dealership and used-car financing offers are quoted as a flat rate, often called an 'add-on rate.' Always ask for the APR-equivalent figure before signing.
Some personal loan and buy-now-pay-later products use flat-rate pricing because the lower-looking headline number is more attractive in marketing materials.
Some Murabaha (cost-plus) structures apply a flat markup on the full asset price, spread evenly across the term — economically similar to a flat rate, even though the underlying contract is a trade sale, not interest.
Flat-rate pricing is extremely common in microfinance and informal lending markets worldwide, where reducing-balance disclosure requirements may be weaker or unenforced.
Interest or markup calculated on the full original principal for the entire loan term, regardless of how much has already been repaid. Always more expensive in real dollars than the same headline percentage as a reducing-balance APR.
The standardized annualized cost of borrowing, typically calculated on a reducing balance. The decreasing balance means less interest accrues as the loan term progresses.
The reducing-balance APR that would produce the exact same monthly payment as a given flat-rate loan over the same term. The honest way to compare a flat-rate offer against a true APR offer.
A loan structure where interest is calculated only on the amount currently owed, not the original amount. As you pay down principal, the interest charge for each subsequent period shrinks accordingly.
Another common name for a flat rate, especially in auto and consumer lending. The interest is 'added on' to the principal upfront, then the total is divided into equal payments.
US federal law requiring lenders to disclose the Annual Percentage Rate for consumer credit, designed specifically to let borrowers compare offers regardless of how the rate is marketed.
APR (Annual Percentage Rate) on a standard loan is charged on the reducing balance — as you pay down the principal each month, the interest charge that month applies only to what you still owe. A flat rate is charged on the full original loan amount for the entire term, even in the final month when you've nearly paid off the loan. Because of this, a flat rate of a given percentage almost always costs significantly more in total dollars than an APR of the same headline percentage.
On a 5-year loan, a 5% flat rate typically converts to roughly 9–9.5% effective APR on a reducing-balance basis. This is because the flat rate keeps charging interest on the original full amount even after you've repaid most of it — effectively, you're paying interest twice on the portion you've already returned. The longer the term, the bigger this gap becomes. This calculator shows you the exact effective APR for any flat rate you enter.
There's no simple multiplication formula — the accurate method calculates the flat-rate loan's fixed monthly payment, then works backward to find what reducing-balance APR would produce that same monthly payment over the same term. This calculator does that calculation automatically using a standard amortization formula solved numerically. As a rough rule of thumb, the effective APR is often roughly 1.8–2x the flat rate for typical 3-7 year terms, but the exact multiplier depends on the term length.
Not necessarily — it depends on the headline rates being compared. A 4% flat rate (≈7-7.5% effective APR) can still beat a 9% APR loan for the same amount and term. The point of this calculator isn't that flat rate is always worse — it's that you cannot directly compare the headline percentages. A flat rate and an APR are calculated completely differently, so comparing '5% flat' to '7% APR' as if they're on the same scale is a common and costly mistake.
It varies by structure. Murabaha (cost-plus) financing typically uses a flat markup calculated on the full asset price and divided evenly across the term — economically similar to a flat rate, though structured as a trade sale rather than interest. Musharakah (diminishing partnership) financing charges rent only on the bank's remaining equity share, which decreases over time — economically more similar to a reducing-balance structure. Always ask any provider, halal or conventional, for the effective APR so you can compare offers on equal footing.
Flat rates are simpler to calculate and explain, and the lower headline percentage makes the financing appear more attractive at a glance — '5% flat' sounds cheaper than '9% APR' even when the dollar cost is identical or higher. Flat-rate structures are common in auto loans, some personal loans, and certain Islamic financing products. Many jurisdictions require lenders to disclose an Annual Percentage Rate equivalent specifically so consumers can make accurate comparisons regardless of how the rate is marketed.
In the United States, the Truth in Lending Act (TILA) generally requires lenders to disclose the Annual Percentage Rate for consumer credit, including loans that may be marketed using a flat or 'add-on' rate. Requirements vary by loan type and jurisdiction outside the US. Regardless of legal requirements, always ask explicitly for the APR-equivalent figure, or use this calculator, before agreeing to any flat-rate financing.
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Read the guideThis calculator computes the effective APR of a flat-rate loan numerically by matching monthly payments to a standard reducing-balance amortization formula. Results are estimates for educational comparison purposes only. Actual loan terms, fees, and disclosure requirements vary by lender and jurisdiction. Not financial or legal advice. Always request the official APR disclosure from any lender before agreeing to financing.