Mortgage Calculator
How Mortgage Calculations Work
A mortgage calculator helps you estimate your monthly payment and understand the total cost of homeownership. It considers the principal loan amount, interest rate, loan term, and additional costs like property taxes, insurance, and PMI to give you a complete picture of your monthly housing expense.
Understanding your mortgage payment is crucial for budgeting and determining how much house you can afford. The calculation uses an amortization schedule where early payments go mostly toward interest, and later payments apply more toward the principal balance.
Mortgage Calculation Formula
Monthly Principal & Interest Payment
M = P × [r(1+r)^n] / [(1+r)^n - 1]
Where:
M = Monthly payment
P = Principal loan amount (home price - down payment)
r = Monthly interest rate (annual rate ÷ 12)
n = Total number of payments (years × 12)
Total Monthly Payment (PITI)
Total Payment = Principal & Interest + Property Tax + Insurance + PMI
Property Tax (monthly) = Annual Property Tax ÷ 12
Insurance (monthly) = Annual Insurance ÷ 12
PMI (monthly) = If down payment < 20%, typically 0.3-1.5% of loan amount annually
Key Calculations
- Loan Amount: Home Price - Down Payment
- Down Payment %: (Down Payment ÷ Home Price) × 100
- Total Interest: (Monthly Payment × Total Payments) - Principal
- Total Cost: Home Price + Total Interest + Fees
Examples
Example 1: Conventional 30-Year Mortgage
Home Price: $400,000
Down Payment: $80,000 (20%)
Loan Amount: $320,000
Interest Rate: 6.5% annually
Term: 30 years
Monthly P&I: $2,022
Total Interest: $407,920
Example 2: Low Down Payment with PMI
Home Price: $300,000
Down Payment: $15,000 (5%)
Loan Amount: $285,000
Interest Rate: 7.0% annually
PMI: $142/month (0.6% annually)
Monthly P&I: $1,898
Total Monthly (with PMI): $2,040
Example 3: 15-Year Mortgage
Home Price: $350,000
Down Payment: $70,000 (20%)
Loan Amount: $280,000
Interest Rate: 6.0% annually
Term: 15 years
Monthly P&I: $2,366
Total Interest: $145,880