Mortgage Calculator
Full mortgage payment breakdown - monthly P&I, total interest, and a year-by-year amortization schedule showing principal vs interest split.
About the Mortgage Calculator
The Mortgage Calculator produces a complete, lender-grade picture of any home loan: monthly principal and interest, full PITI (with property tax, homeowners insurance, HOA, and PMI), total interest paid over the life of the loan, and a year-by-year amortization schedule showing exactly how each payment splits between principal and interest.
Beyond the basic payment, the calculator models extra-payment scenarios (one-time, monthly, or annual) so you can see how much interest you skip and how much earlier you pay off. It also flags the month PMI auto-drops at 78% loan-to-value, and shows side-by-side comparisons of 15-year vs 30-year structures at the same purchase price.
Common use cases
- Compare 15-year, 20-year, and 30-year mortgage options
- See exactly how much an extra $200/month payment saves in interest
- Stress-test affordability at rate increases of 0.5%, 1%, 2%
- Plan a refinance by comparing existing balance amortization to new-loan amortization
Tips for accurate results
Focus on total interest paid over the life of the loan, not just the monthly payment. Two mortgages with the same monthly payment can have wildly different total interest depending on the term - a 30-year is roughly 2x the interest of a 15-year at the same rate. The amortization schedule shows the brutal math: early payments are mostly interest.
Privacy & data handling
The Mortgage Calculator runs entirely in your browser. Nothing you enter is uploaded, logged, or shared with third parties - the math happens locally and your inputs disappear when you close the tab. There is no signup, no email collection, and no daily-use limit.
How is a monthly mortgage payment calculated?
Principal & interest follows the standard amortization formula: P × [r(1+r)^n] / [(1+r)^n − 1], where P is principal, r is monthly rate (annual ÷ 12), and n is number of payments. The tool adds optional property tax, homeowners insurance, HOA, and PMI to give the full PITI payment.
Why does most of my early payment go to interest?
Interest is charged on the remaining balance each month. Early on, the balance is high, so the interest portion of your fixed payment is huge - often 80%+ in year 1. As you pay down principal, the balance shrinks, less interest accrues, and more of each payment goes to principal. The crossover (50/50 split) usually happens around year 15-18 of a 30-year loan.
Should I take a 15-year or 30-year mortgage?
A 15-year loan saves enormously on total interest (often 60%+ less) and builds equity faster, but the monthly payment is ~50% higher. A 30-year keeps payments low and frees cash for investing - if you can reliably earn more than your mortgage rate elsewhere, the 30-year math wins. Most people split the difference: 30-year loan with optional extra payments.
How much does an extra payment per year save?
One extra full payment per year on a 30-year loan shortens it by roughly 4-5 years and saves tens of thousands in interest, depending on rate. The amortization view in this tool lets you input recurring or one-time extra payments to see exactly how much interest you skip and how soon you pay off.
What is PMI and when does it go away?
Private Mortgage Insurance is required when you put down less than 20%. It typically costs 0.3-1.5% of the loan annually. By federal law, it automatically cancels when your loan balance reaches 78% of the original purchase price, but you can request removal at 80% - the tool flags both dates in the amortization schedule.
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