Simple Mortgage Calculator
Estimate monthly mortgage payments based on loan amount, interest rate, and term.
How This Mortgage Calculator Works
This calculator estimates your monthly mortgage payment using three inputs: the total loan amount, the annual interest rate, and the loan term in years. The calculation assumes a fixed-rate mortgage with equal monthly payments over the full term.
The formula used is the standard amortization formula:
M = P × [r(1+r)^n] / [(1+r)^n – 1]
Where:
- M = monthly payment
- P = principal loan amount
- r = monthly interest rate (annual rate divided by 12)
- n = total number of monthly payments (loan term in years × 12)
The result shows your estimated principal and interest payment only. It does not include property taxes, homeowners insurance, or private mortgage insurance (PMI), which are typically added to your actual monthly payment.
How to Use the Calculator
- Enter the total loan amount you expect to borrow.
- Input the annual interest rate as a percentage (for example, 6.5 for 6.5%).
- Set the loan term in years (common terms are 15, 20, or 30 years).
- Click calculate to see your estimated monthly payment.
Adjust any input to see how changes in loan amount, rate, or term affect your payment. This helps you compare different borrowing scenarios before committing to a loan.
Example Calculation
For a $300,000 loan at 6.5% annual interest with a 30-year term:
- Monthly interest rate: 0.5417% (6.5% ÷ 12)
- Number of payments: 360 (30 years × 12 months)
- Estimated monthly payment: approximately $1,896
Over the full 30-year term, total interest paid would be roughly $382,000. This illustrates how interest rate and term length significantly affect total borrowing cost.
Understanding Your Results
The calculated payment represents only the principal and interest portion of your mortgage. Your actual monthly housing cost will be higher and should include:
- Property taxes – varies by location and property value
- Homeowners insurance – required by lenders
- Private mortgage insurance (PMI) – typically required if your down payment is less than 20%
- HOA fees – if applicable for your property
Use this calculator as a starting point for budgeting. For a complete picture, add estimated taxes and insurance to the result. Many lenders use a debt-to-income ratio guideline of 28% for housing costs, meaning your total monthly housing payment should not exceed 28% of your gross monthly income.
Common Mistakes to Avoid
- Entering the purchase price instead of the loan amount. The calculator needs the amount you are borrowing, not the home's total price. Subtract your down payment from the purchase price to get the loan amount.
- Using the wrong interest rate format. Enter the annual rate as a percentage number. For example, 6.5% should be entered as 6.5, not 0.065.
- Ignoring additional costs. The result is not your total monthly housing expense. Always budget for taxes, insurance, and potential PMI.
- Assuming the rate is fixed for the entire term. This calculator assumes a fixed-rate mortgage. Adjustable-rate mortgages (ARMs) have rates that can change after an initial period.
Limitations
This calculator provides estimates only. Actual mortgage payments depend on your specific loan terms, credit profile, lender fees, and local tax rates. The calculation does not account for:
- Variable or adjustable interest rates
- Balloon payments or interest-only periods
- Prepayment penalties
- Closing costs or origination fees
- Escrow account requirements
Always consult with a licensed mortgage professional for personalized loan estimates and pre-approval.
Practical Use Cases
- Budget planning: Determine if a target home price fits within your monthly budget before starting your home search.
- Rate comparison: Compare how different interest rates from multiple lenders affect your monthly payment.
- Term evaluation: Decide between a 15-year and 30-year mortgage by comparing monthly payments and total interest costs.
- Down payment analysis: See how increasing your down payment reduces the loan amount and monthly payment.
Frequently Asked Questions
Does this calculator include taxes and insurance?
No. The result shows only principal and interest. Property taxes, homeowners insurance, and PMI are separate costs that vary by location and loan specifics. Add estimated amounts for these to get a realistic monthly housing cost.
What is a good debt-to-income ratio for a mortgage?
Most lenders prefer a front-end DTI (housing costs only) of 28% or less and a back-end DTI (all monthly debts) of 36% or less. Some loan programs allow higher ratios with compensating factors.
How accurate is this calculator?
It is mathematically accurate for fixed-rate amortization. However, actual loan terms, fees, and rate locks can cause slight differences. Use it as a planning tool, not a final loan quote.
Can I use this for an adjustable-rate mortgage (ARM)?
The calculator assumes a fixed rate for the entire term. For an ARM, the initial payment may be lower, but payments can increase after the fixed period ends. This tool does not model rate adjustments.
What is PMI and when do I need it?
Private mortgage insurance protects the lender if you default. It is typically required when your down payment is less than 20% of the home's purchase price. PMI costs vary but generally range from 0.3% to 1.5% of the loan amount annually.
How does loan term affect my payment?
Shorter terms like 15 years have higher monthly payments but significantly less total interest paid over the life of the loan. Longer terms like 30 years have lower monthly payments but more total interest. Use the calculator to compare both scenarios.