P = principal, r = monthly rate (annual rate ÷ 12), n = number of payments (years × 12). Because interest is charged on the outstanding balance, it's heaviest at the start — so even small extra payments early on cut the total interest and shorten the loan significantly.
How the loan calculator works
This calculator uses the standard fixed-rate amortization formula to work out your monthly payment on a loan such as a personal loan, auto loan, or mortgage (principal and interest only). Drag any slider and every figure — payment, interest, payoff — updates instantly.
How much loan can you afford?
Lenders lean on the 28/36 rule: housing costs at or under 28% of gross monthly income, and all debt payments — this loan included — under 36%. As a borrower, flip it around: on a $6,000 gross monthly income, that caps combined debt payments near $2,160. Work backwards in the calculator — set the rate and term you expect, then drag the amount until the payment fits your ceiling with margin. A payment that only works in a perfect month doesn't work.
The power of extra payments
Use the extra-payment slider to see how paying a little more each month shortens your loan and slashes total interest. Because interest is charged on the remaining balance, every extra dollar of principal compounds into real savings over the life of the loan.
Worked example
Borrow $20,000 at 8% APR over 5 years: the monthly rate is 0.667%, n = 60 payments, giving a payment of about $406/month and $4,332 of total interest. Add just $50/month extra and the loan clears roughly 7 months sooner, saving about $600 in interest — the earlier in the loan, the bigger the effect.
Reading your amortization schedule
The schedule below the results lists every payment split into interest and principal with the running balance. Notice the shape: in month 1 of the example above, $133 of the $406 is interest; by the final year it's under $20. That front-loading is why refinancing or extra payments matter most in a loan's early years, and why the halfway point in time is not the halfway point in interest.
Interest rate vs APR
The interest rate prices the borrowing itself; APR additionally folds in lender fees, making it the better number for comparing offers. This calculator amortizes whatever rate you enter. Buying a home or car specifically? The mortgage calculator adds taxes and insurance, and the auto loan calculator handles trade-ins and sales tax; for paying down a card, see the debt payoff calculator.
Estimates principal and interest only; for information, not financial advice.
What counts as a good rate?
There is no universal "good" number — rates track the central-bank environment and your credit profile. What generalizes: moving between credit tiers routinely swings personal-loan APRs by 5–15 percentage points, secured loans (auto, home) price far below unsecured ones, and shorter terms price below longer ones. The practical move is comparing your offers, not headlines: get quotes from 2–3 lenders in the same week (scoring models treat clustered inquiries as one search), enter each offer's APR here, and let the total-interest figure — not the monthly payment — pick the winner.