What is a US Mortgage Calculator?
A US mortgage calculator estimates your monthly principal and interest payment on a home loan, along with total interest paid over the life of the loan. It uses the standard amortisation formula used by all US lenders — banks, credit unions, and mortgage companies regulated by the Consumer Financial Protection Bureau (CFPB).
US mortgages typically come in 15-year and 30-year fixed terms, or 5/1, 7/1, and 10/1 Adjustable Rate Mortgages (ARMs). Understanding your monthly payment before house-hunting sets realistic price limits and prevents overextending your budget.
How Mortgage Payment is Calculated
M = P × [r(1+r)ⁿ] / [(1+r)ⁿ − 1]
Where M = monthly payment, P = principal loan amount, r = monthly interest rate (annual ÷ 12), n = total payments (years × 12). Note: this is principal + interest only — your actual monthly payment will also include property tax escrow, homeowner's insurance, and possibly PMI.
- 30-year fixed: Lower monthly payment, higher total interest. Best for budget-conscious buyers or those who plan to invest the payment difference.
- 15-year fixed: Higher monthly payment, significantly less total interest (~40-50% savings). Best for those who can comfortably afford the higher payment.
- ARM loans: Lower initial rate, but can adjust up after the fixed period. Suitable if you plan to sell or refinance before the adjustment kicks in.
How much house can I afford in the US?
The standard guideline is the 28/36 rule: housing costs should not exceed 28% of gross monthly income, and total debt payments should not exceed 36%. For a $100,000/year income ($8,333/month gross), maximum housing payment = $2,333/month. With current mortgage rates (~6.5–7%), this supports a loan of approximately $350,000–$380,000 — meaning a $430,000–$460,000 home with 20% down.
What is PMI and when can I avoid it?
Private Mortgage Insurance (PMI) is required by most lenders when your down payment is less than 20% of the home price. PMI costs 0.5–1.5% of the loan amount annually (~$100–$300/month on a $300,000 loan). You can request PMI cancellation once your equity reaches 20% (home value appreciation counts). With 20% down, you avoid PMI entirely — saving tens of thousands over the loan term.
What is the difference between pre-qualification and pre-approval?
Pre-qualification is an informal estimate based on self-reported financial information — it takes minutes and has no credit impact. Pre-approval involves a full credit check and income/asset verification by a lender — it carries more weight with sellers and locks in a rate for 60–90 days. In competitive markets, sellers often require pre-approval letters with offers. Get pre-approval from 2–3 lenders to compare rates; multiple hard inquiries within 14–45 days count as one inquiry for FICO scoring purposes.
Should I choose a fixed or adjustable rate mortgage?
Fixed rates give payment certainty for the life of the loan — ideal if you plan to stay in the home long-term or if current rates are historically low. ARMs offer a lower initial rate (often 0.5–1% lower than 30-year fixed) but reset periodically after the initial fixed period. If current 30-year fixed rates are above 7%, a 5/1 ARM at 5.5% can save significant money if you plan to sell or refinance within 5 years.
Last Updated: March 2026 · For US audiences