APR Calculator

It converges to an APR identical to the stated Interest Rate. With Total Loan Fees at $0, the net loan the solver targets (line 28, Loan Amount minus Total Loan Fees) equals the full loan amount, so there's no fee-driven wedge to solve for — verified directly by setting fees to $0, which returns an APR of exactly 6.5% and an APR vs Rate Difference of exactly 0.

Interest Rate, overwhelmingly — its ±10% span shifts APR by roughly a fifth of APR, while the same ±10% span on Loan Amount, Total Loan Fees, or Loan Term each moves it by well under 1%. The Newton-Raphson solver (lines 35-72) starts its guess at the stated Interest Rate and only adjusts it upward to account for fees, so the stated rate remains the dominant input to the final APR figure.

Neither one clearly leads — Loan Amount and Total Loan Fees move APR vs Rate Difference by a comparably sized ±10% span, roughly 21% and 20% of APR vs Rate Difference respectively. That's because the fee-driven gap between APR and the stated rate depends on fees relative to the loan amount, not on either dollar figure by itself: a bigger loan dilutes the same fees into a smaller rate bump.

No — the solver targets a net loan of Loan Amount minus Total Loan Fees (line 28), meaning it assumes those fees are effectively paid out of the loan proceeds rather than financed into a larger loan balance. If a lender instead rolls fees into the loan amount itself, the true APR impact would differ from what this calculator reports.

Up to 100 times (line 32), each refining the guessed rate using a Newton-Raphson derivative approximation (lines 53-65), and it stops early once the calculated payment matches the target monthly payment to within 0.0000001 (line 33). In practice this converges in only a handful of iterations for realistic loan amounts, rates, and fees.