Before embarking on a property purchase, it's essential to simulate your mortgage to know your monthly payments, total loan cost and debt capacity. An online simulator lets you adjust parameters in real time: loan amount, term, interest rate and down payment.
Mortgage monthly payment calculation is based on the constant annuity formula. The monthly payment depends on the loan principal, the monthly interest rate and the loan term in months. The 28% rule (housing cost-to-income ratio) is a common US benchmark: your monthly housing payment should not exceed 28% of your gross monthly income. For total debt, lenders typically use the 36% DTI rule.
📐 Formula
Monthly payment = Principal × [monthly_rate / (1 - (1 + monthly_rate)^(-n))] | Monthly rate = Annual rate / 12
📊 Reference table
| Loan amount | Term | Rate 6 % | Rate 6.5 % | Rate 7 % |
|---|---|---|---|---|
| $200,000 | 20 years | $1,432/mo | $1,491/mo | $1,551/mo |
| $300,000 | 20 years | $2,149/mo | $2,237/mo | $2,326/mo |
| $400,000 | 30 years | $2,398/mo | $2,528/mo | $2,661/mo |
| $500,000 | 30 years | $2,997/mo | $3,160/mo | $3,327/mo |
💡 Practical examples
Example 1: borrowing capacity with $6,000/month gross income
Max payment (28% rule) = $6,000 × 28% = $1,680. At 7% over 30 years, borrowing capacity ≈ $252,000. With 10% down payment, home price ≈ $280,000.
Example 2: total cost of a $300,000 mortgage over 30 years
Rate 7%: monthly payment = $1,996. Total paid = 1,996 × 360 = $718,560. Interest cost = $418,560. That's 139% of the original principal.
Example 3: impact of term on monthly payment
For $300,000 at 7%: 15 years → $2,696/month (total interest: $185,280). 30 years → $1,996/month (total interest: $418,560). Going from 15 to 30 years saves $700/month but costs $233,280 more.