Mortgage Calculator
See your monthly mortgage payment and the full amortization breakdown — principal vs. interest, year by year.
What this calculator does
Calculates your monthly mortgage payment (principal and interest) and total interest paid over the life of the loan, using the standard fixed-rate amortization formula every US lender uses.
Who this is for
Homebuyers comparing loan terms or rates before shopping for a mortgage, anyone checking whether a specific home price fits their budget, or people deciding between a 15-year and 30-year term.
How this calculator works
This uses the standard fixed-rate amortization formula: P × r / (1 − (1+r)^−n), where P is your loan amount, r is the monthly interest rate, and n is the number of monthly payments. It's the same formula every US mortgage lender uses for a fixed-rate loan.
Worked example
A $400,000 home, $80,000 down payment (20%), 6.5% APR, 30-year term: loan amount = $320,000. Monthly payment ≈ $2,022. Over 360 payments, total paid ≈ $728,000, meaning total interest over the life of the loan ≈ $408,000 — more than the original loan amount itself, which is typical for a 30-year term at this rate.
What this result means
Your monthly payment is fixed for the life of the loan, but the split between principal and interest isn't — early payments are mostly interest, and that ratio flips toward principal as the loan matures. Over a 30-year term, it's common for total interest paid to exceed the original loan amount, especially at higher rates, which is why the total-interest figure above often surprises people more than the monthly payment itself.
Principal vs. interest over the life of the loan
Run the calculator above to see how much of your total payments go to principal vs. interest.
Common mistakes
- Forgetting property tax, insurance, and PMI. This calculator shows principal and interest only — your real monthly housing cost is usually meaningfully higher once escrow items are added.
- Not shopping the rate. Even a 0.25-0.5% difference in APR compounds into tens of thousands of dollars over a 30-year term — always get quotes from multiple lenders.
- Ignoring how much extra a shorter term saves. A 15-year loan has a higher monthly payment but dramatically less total interest than a 30-year loan at the same rate.
- Focusing only on the monthly payment, not total interest. Two loans with similar monthly payments (say, a lower rate over 30 years vs. a higher rate over 15) can have vastly different total interest costs — always compare the full picture, not just what fits the monthly budget.
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Frequently Asked Questions
Why can total interest exceed the original loan amount?
Over a 30-year term, interest is calculated on a large remaining balance for many years before it shrinks meaningfully. At typical rates, this compounding effect means total interest paid often exceeds the original loan amount — a 15-year term or extra principal payments both reduce this significantly.
Why is so much of my early payment interest?
Fixed-rate mortgages use amortization, where interest is calculated on the remaining balance each month. Since the balance is highest at the start, interest makes up the largest share of your payment early on, gradually shifting toward principal as the balance shrinks.
Does this include property tax and insurance?
No — this shows principal and interest (P&I) only. Most lenders collect property tax and homeowners insurance in an escrow account added to your monthly payment, so your actual total payment will typically be higher.
How much does a 15-year vs 30-year term actually save?
A 15-year term has a higher monthly payment but can cut total interest paid by more than half compared to a 30-year loan at the same rate, since you're paying down principal much faster.
What down payment do I need to avoid PMI?
Conventional US lenders typically require 20% down to avoid Private Mortgage Insurance (PMI). Below that threshold, PMI is usually added to your monthly payment until you reach 20% equity.