Mortgage Simulator
A mortgage simulator projects how a home loan behaves over its full term, showing the monthly payment, total interest paid, and a complete amortization table. This tool supports the two most common amortization systems: Price (French system), with fixed installments throughout the loan, and SAC (constant amortization system), where the principal portion is fixed so installments start higher and decrease every month. Comparing both side by side reveals which structure fits your budget and long-term cost goals.
The choice between Price and SAC has real financial consequences. With SAC, the outstanding balance falls faster, so total interest over the life of the loan is lower — but the first installments are noticeably larger. With Price, payments are predictable and initially smaller, which eases qualification, at the cost of paying more interest overall. Simulating different down payments, rates, and terms before signing helps you negotiate with banks and avoid overcommitting your monthly income.
How it works
In the Price system, the fixed payment is PMT = PV × i ÷ (1 − (1 + i)⁻ⁿ), where PV is the financed amount, i the monthly interest rate, and n the number of months; each payment mixes interest (balance × i) and amortization (PMT − interest). In the SAC system, amortization is constant at A = PV ÷ n, and each installment equals A plus interest on the remaining balance, so payments decline linearly by A × i each month.
Use cases
- Comparing Price vs. SAC installments and total interest before choosing a home loan
- Estimating the monthly payment for different down payment and term combinations
- Checking whether the first installment fits typical bank limits (around 30% of income)
- Viewing the amortization table to plan early payoff or extra payments
Frequently asked questions
What is the difference between Price and SAC amortization?
Price (the French system) keeps the installment fixed for the whole term, with the interest share shrinking and the amortization share growing over time. SAC keeps the amortization of principal constant, so installments start higher and decrease every month. SAC results in less total interest; Price offers smaller, predictable initial payments.
How is a fixed mortgage payment calculated?
The Price formula is PMT = PV × i ÷ (1 − (1 + i)⁻ⁿ), where PV is the amount financed, i the monthly interest rate as a decimal, and n the number of months. For example, financing 300,000 at 0.8% per month over 360 months gives a fixed payment of roughly 2,428.
Which system pays less interest in total, Price or SAC?
SAC almost always results in lower total interest for the same rate and term, because the principal is repaid faster and interest is charged on a smaller balance each month. The trade-off is that the first SAC installments can be 20-30% higher than the equivalent Price payment.
How does the down payment affect my mortgage?
A larger down payment reduces the financed amount (PV), which lowers both the monthly payment and the total interest proportionally. It can also unlock better interest rates, since a lower loan-to-value ratio represents less risk for the lender.
Can I pay off my mortgage early and save interest?
Yes. Extra payments applied to principal reduce the outstanding balance, and since interest is calculated on that balance each period, every early amortization cuts future interest. Using the amortization table, you can see exactly how much balance remains at any month and how much an extra payment would shorten the term.