Mortgage Calculator

A mortgage payment combines principal, interest, property taxes, homeowner's insurance, and (when down payment is below 20%) private mortgage insurance — the PITI total. The interest portion is computed monthly on remaining principal at the loan rate; payments are amortized so the total stays constant.

The calculator returns the monthly PITI breakdown plus the full amortization schedule for any term and rate.

The amortization formula gives the fixed monthly payment as P × (r(1+r)^n) / ((1+r)^n − 1), where P is principal, r is the monthly interest rate (annual rate divided by 12), and n is the number of monthly payments. The payment stays constant over the loan term; what changes is the split between interest and principal. Early payments are mostly interest because the principal balance is high; later payments are mostly principal as the balance shrinks. For a 30-year fixed at 7%, the first payment is approximately 83% interest, by year 15 roughly 50/50, by year 25 mostly principal. This front-loaded structure is why refinancing or selling within the first few years sees relatively little equity buildup.

A worked example: $400,000 home, $80,000 down (20%), $320,000 financed at 7% for 30 years. Monthly principal+interest = $2,129. Add property tax of $5,000/year ($417/month) and homeowner's insurance of $1,800/year ($150/month). PITI total = $2,696/month. With 20% down, no PMI required. Total interest paid over 30 years = $446,428 — more than the original loan amount. Paying an extra $200/month on principal cuts the term to roughly 24 years and saves about $115,000 in interest. The amortization schedule shows month-by-month breakdown for stress-testing scenarios.

Limitations: the calculator handles fixed-rate loans cleanly. Adjustable-rate mortgages (ARMs) require modeling future rate adjustments, which depend on index rates that aren't predictable. Interest-only loans, balloon payments, and graduated-payment mortgages have different structures. Property tax estimates use your input — assessor revaluation can shift this significantly year-over-year. Insurance varies by region (Florida and California cost more for hurricane and wildfire exposure). PMI calculation here uses 0.5–1% of loan annually as the typical range; specific PMI premium depends on credit score and LTV ratio. HOA fees, special assessments, and maintenance reserves aren't included — budget separately.