Calculate Your Mortgage
+ Add Property Tax, Insurance & PMI
Your Results
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How to Use the Mortgage Calculator
Using the Calcus mortgage calculator is straightforward. Enter your home price, down payment amount, loan term, and annual interest rate. The calculator instantly shows your monthly mortgage payment, total interest paid over the life of the loan, and a complete amortization schedule breaking down every payment.
You can also expand the optional section to include property taxes, homeowner's insurance, and PMI (private mortgage insurance) to get a more complete picture of your true monthly housing cost.
How Monthly Mortgage Payments Are Calculated
Your monthly mortgage payment is calculated using a standard amortization formula. The formula takes three inputs: your loan principal (home price minus down payment), your monthly interest rate (annual rate divided by 12), and your total number of payments (loan term in years multiplied by 12).
The formula is: M = P × [r(1+r)^n] / [(1+r)^n - 1]
Where M is the monthly payment, P is the loan principal, r is the monthly interest rate, and n is the number of monthly payments. Early in the loan, most of your payment goes toward interest. Over time, the portion going toward principal grows — this is called amortization.
30-Year vs 15-Year Mortgage
The two most common mortgage terms in the US are 30-year and 15-year fixed loans. A 30-year mortgage has lower monthly payments but you pay significantly more interest over the life of the loan. A 15-year mortgage has higher monthly payments but you build equity faster and pay far less total interest. Use the loan term dropdown to compare both options side by side.
What Is a Good Mortgage Rate?
Mortgage interest rates change daily based on economic conditions. Your personal rate depends on your credit score, loan type, down payment, and the lender. Generally, a credit score above 740 qualifies you for the best available rates. Shopping with at least 3 lenders is the most effective way to find a competitive rate for your situation.
How Much House Can You Afford?
A widely used rule of thumb is that your monthly housing costs should not exceed 28% of your gross monthly income. Your total debt payments (including car loans, student loans, and credit cards) should stay below 43% of gross income — this is what lenders call the debt-to-income ratio. Use this calculator to test different home prices and see which payment fits comfortably within your budget.