Compare SAC and PRICE financing systems side by side.
In Brazil, housing loans typically use SAC or PRICE amortization. In SAC (Constant Amortization System), the principal is paid in equal amounts every month, the financed amount divided by the number of installments, while interest decreases with the balance, resulting in higher initial installments that shrink over time. In PRICE (Fixed Installment System), all installments are equal, computed with the annuity formula; more interest is paid early and more principal at the end. SAC tends to cost less in total interest because the balance falls faster, while PRICE offers predictable cash flow. This tool builds both schedules from the same rate and term and shows the difference in total interest.
In SAC, amortization is constant: you divide the financed amount by the number of installments and add, each month, the interest charged on the remaining balance. Because the balance falls linearly, monthly interest drops and the installment shrinks from first to last. In PRICE, the installment is fixed and computed with the uniform-series formula, PMT = P × i × (1+i)ⁿ ⁄ [(1+i)ⁿ − 1], so the interest share is largest at the start and the amortization share grows over time.
The annual rate you enter is treated as nominal and converted to a monthly rate by compound capitalization, (1 + i)^(1/12) − 1, before either schedule is built. In the end, the tool sums everything paid under each system: because SAC clears the balance faster, its total interest is usually lower than PRICE's for the same rate and term.
Illustrative example, R$ 120,000 financed over 120 months: in SAC the amortization is fixed at R$ 1,000 per month (120,000 ÷ 120), added to the interest on the outstanding balance, so the first installment is the highest and the last the lowest. In PRICE, at the same rate and term, every installment is equal, easier to budget, but the debt stays high for longer.
Because the balance falls faster in SAC, the total interest over the contract tends to be lower than in PRICE; that gap is exactly what the tool reports as the SAC saving. On the other hand, a borrower with a tighter budget early on may prefer PRICE's fixed, lower first installments.
The simulation uses a fixed nominal rate and does not include IOF, insurance (such as MIP and DFI on real estate loans), administration fees, or monetary correction. In indexed contracts (for example IPCA+ or TR-linked lines), the real installments may diverge from what is shown here, especially over long terms, because the balance is periodically restated by the index.
Treat the result as a mathematical reference to compare the two systems, not as the bank's final offer. Before signing, check the Total Effective Cost (CET) disclosed in the proposal, which combines interest, fees and insurance into a single comparable rate.
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></iframe>These references help contextualize formulas, standards, APIs and limitations used on this page. They do not replace professional validation when a result has legal, financial, medical or operational impact.
SAC is generally cheaper in total interest because the outstanding balance decreases faster, reducing the base for monthly interest charges. In PRICE, amortization is small at the start, so interest accumulates for longer. For the same rate and term, that gap shows up in the simulation as the SAC saving, which can reach tens of thousands of reais on long loans.
⚠️ Educational simulation. Real estate financing may include insurance (MIP, DFI), administration fees and TR/IPCA correction not included here.
SAC saves R$ 197.434,91 in total interest.
Resolution CMN 3.121/2003 (amortization systems). Rate entered by user, not provided by the tool.
Outstanding balance
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