APR vs Flat Rate Comparison Calculator

Flat rate is a misleading way to quote loan interest. It charges interest on the full original principal for the full term, even as the balance is paid down. A 5% flat rate on a 5-year loan is roughly equivalent to 9-10% APR — close to double, because APR accounts for the declining balance.

This calculator takes a flat rate loan quote and estimates an APR-equivalent figure using a common 1.85× rule of thumb. The result is a useful comparison number, not a regulatory APR. Comparing flat rates against APR-quoted loans on a like-for-like basis usually requires this kind of conversion.

Flat rates appear in some subprime and auto loan markets because they look lower than APR. Many jurisdictions require APR disclosure on consumer credit, but flat rates still surface in specific lender marketing and in non-consumer lending products.

A worked example

For a loan of 10,000 in local currency at a 5% flat rate over 5 years, the tool returns an estimated APR equivalent of 9.25%. The flat-rate total interest is 2,500 and the flat-rate total paid is 12,500. The headline rate scales only with the flat rate; the cash figures scale with the loan amount, so a 7,000 loan at the same rate produces 1,750 interest and 8,750 total paid for the same 9.25% APR estimate. Adjusting any input updates the result as you type.

What moves the number most

The result responds to Loan Amount, Flat Rate Quoted, and Loan Term. The flat rate and the term drive most of the change in the APR estimate; the loan amount scales the cash figures (interest, total paid) without changing the rate result.

The formula behind this

Flat-rate total interest = loan × flat rate × years. Flat-rate monthly payment = total paid ÷ months. The APR equivalent is approximated as 1.85 × flat rate, a common rule of thumb that holds reasonably well for 3-7 year terms. The 1.85 multiplier is an estimate, not an exact APR conversion — a precise APR requires solving for the rate that discounts an amortising payment schedule back to the loan amount.

Why the secondary figures use flat-rate logic

The Monthly Payment, Total Interest, and Total Paid in the secondary panel reflect the flat-rate contract — the amounts a borrower would actually pay under the quoted flat-rate terms. The headline APR figure is the comparison rate against APR-quoted alternatives. The two are deliberately presented side by side so the gap is visible.

What this doesn't capture

Real loan journeys include missed payments, fee changes, early repayment charges, and promotional rates that reset. The calculation assumes a steady plan and uses an approximate APR conversion; reality varies. The figure works as a comparison estimate against APR-quoted alternatives, not as a regulatory APR.