Loan Payment and Total Interest
ConvertEverything runs locally in your browser — nothing is uploaded
Enter the loan amount and pick a rate and term to get the monthly payment, the total interest, and a folded amortisation schedule. The three things that go wrong most often are handled the way banks do them: · The monthly rate is the annual rate ÷ 12 (nominal), not the effective `(1 + rate)^(1/12) - 1`. The effective rate gives a lower payment that does not match your statement. · Equal principal falls every month, so the first and last payments are both shown; a single figure would be wrong. · The final period is forced to zero: rounding interest to the cent leaves a few cents of drift after hundreds of periods, so the last principal is set to the remaining balance. Prepayment can shorten the term or reduce the payment; the two differ, and the result shows the interest saved and the periods (or payment) saved. Everything runs in your browser.
Features
- Equal payment: one fixed monthly payment, plus total interest
- Equal principal: first and last payments both given, because the payment falls every month
- ⚠️ The monthly rate is nominal (annual ÷ 12), and the result says so
- ⚠️ The final period is forced to zero, so the principal repaid equals the loan exactly
- Extra monthly prepayment and one-off lump sums are both supported
- Prepayment can shorten the term or reduce the payment, with the interest saved worked out
- The schedule is folded: first 12 months plus one row per year end, never 360 rows
- Runs entirely in your browser
How to use
- Enter the loan amount
- Pick the repayment method and enter the rate and term (years or months)
- For prepayment, set the extra monthly amount and any lump sum with its period
- The result gives the payment, total interest, schedule and interest saved
FAQ
- Why does my payment differ by a few cents from the bank?
- Because each period interest is rounded to the cent here, while a bank may keep more internal precision. Over hundreds of periods the last few differ slightly. This tool forces the final balance to exactly zero, so the totals reconcile with the principal.
- Why two figures for equal principal?
- Because the payment is not fixed: a constant amount of principal is repaid each month, so the interest, and the payment, falls. The first is the highest and the last the lowest; one number would mislead.
- Shorten the term or reduce the payment?
- They differ. Shortening keeps the payment and cuts periods, usually saving more interest; reducing keeps the term and lowers each payment, easing cash flow. Both are computed here with concrete figures.
- Nominal or effective rate?
- Nominal: the monthly rate is the annual rate divided by 12. That is how banks do it. The effective monthly rate, (1 + annual)^(1/12) - 1, is smaller and gives a lower payment the bank will not recognise.
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