Total Interest Paid Calculator
Find out how much you pay in interest alone over a loan with the French (Price) amortization. Enter the installment, the number of months and the amount financed.
Total interest
—
Total interest paid on a loan
Add up every installment you pay, subtract the principal you borrowed, and what's left is the total interest: total_interest = Σ PMT − PV. Under the Price system every PMT is identical, which collapses the math to n·PMT − PV. Under SAC the installments shrink from one month to the next, and you end up paying less interest overall since the balance comes down faster.
Take R$ 100,000 at 1% per month over 100 months. Price gets you to roughly R$ 58,700 in interest; SAC lands around R$ 50,500. That R$ 8,200 gap is what a flat installment costs you, the price tag on the convenience of paying the same amount every month. If you want an honest comparison between offers, look at the CET (Custo Efetivo Total). It rolls in fees, IOF and insurance instead of stopping at the headline rate.
Real-world applications
This is the number behind everyday money decisions: budgeting, weighing Price against SAC, picking a term (stretch it out and the installment drops, but the interest bill balloons), running the numbers on a refinance, or deciding whether to throw extra cash at the balance. On a mortgage, trimming even 12 months off the term through amortizações extras can save you tens of thousands of reais in interest.
FAQ
Why does Price always pay more interest than SAC? The outstanding balance drops more slowly under Price, so interest keeps piling up on a bigger number for longer.
Does total interest equal the CET cost? No. Total interest covers only the interest itself. CET goes further and adds IOF, registration fees, opening fees and mandatory insurance, all expressed as an annual rate.
Is a longer term always worse? You'll always pay more interest in total, but the monthly bite is lighter. When cash is tight, a longer term paired with voluntary amortizações can be a fair compromise.
Related Tools
Loan Calculator
Simulate loans and financing with a full amortization table. Calculate installments, total interest, and the real cost of credit.
Z-spread (Zero-Volatility Spread)
Computes a bond's Z-spread: the constant spread added to the entire zero (spot) rate curve so the present value of its cashflows equals the market price. Unlike the nominal spread, which uses a single point, it accounts for the whole shape of the curve; for an option-free bond the Z-spread equals the OAS. Enter the cashflow times and amounts, the zero rate at each node and the price; the result is in basis points.
Payer Swaption (Black Model)
Computes the premium of a payer swaption with the Black model: the right to enter an interest rate swap paying a pre-agreed fixed rate. The price is the swap's annuity multiplied by a Black formula on the forward swap rate. Swaptions are the central instrument for those managing long-term interest rate risk, like banks and insurers. Enter the forward swap rate, the strike, the volatility, the expiry, the annuity (PV01) and the notional.
Loan Constant (Mortgage Constant)
Computes the loan constant, also called the mortgage constant: the annual debt service divided by the original loan amount, as a percentage. It shows directly what fraction of the principal you pay per year, combining interest and amortization. In real estate, comparing the loan constant with a property's cap rate immediately reveals whether the financing produces positive or negative leverage. Enter the annual debt service and the loan amount.
First Million Calculator
Compute how long it takes to reach R$1,000,000 given a monthly contribution and compound interest rate.
Interest Rate Caplet (Black Model)
Computes the premium of a caplet with the Black model: an option that pays when a period's interest rate exceeds a cap. A full interest rate cap is a sum of caplets, one for each payment period. It's the classic protection for someone who took a floating-rate loan and wants to limit how much they can pay. The price discounts the expected payoff to the payment date. Enter the forward rate, the cap rate, the volatility, the fixing time, the accrual fraction, the discount factor and the notional.
The results provided by this tool are for general informational and educational purposes only and do not constitute professional, financial, medical, legal, tax or accounting advice. Always confirm important decisions with a qualified professional and official sources.