Mortgage Calculator — Monthly Payment & Amortization

A mortgage calculator helps you estimate your monthly payment, total interest paid, and the full cost of a home loan before signing any agreement. It is one of the most essential financial planning tools available to homebuyers, real estate investors, and financial advisors — used to compare loan offers, evaluate affordability, and plan long-term household budgets. This calculator uses the standard amortization formula endorsed by the Consumer Financial Protection Bureau (CFPB).

In a fixed-rate mortgage, the monthly payment remains constant for the entire loan term — typically 15 or 30 years. Each payment is split between principal (reducing your loan balance) and interest (the lender's fee). In the early years of a mortgage, the majority of each payment goes to interest. As the loan matures over time, an increasing portion goes to principal — this process is called amortization.

Understanding your full mortgage costs before purchasing is critical for sound financial planning. On a $300,000 home with a 30-year mortgage at 6%, you will pay more than $278,000 in interest alone over the life of the loan — nearly as much as the purchase price itself. This calculator makes those numbers visible upfront so you can make an informed decision.

Example 1 — Starter home, 30 years: $250,000 home, 10% down ($25,000), 6.5% rate, 30 years. Loan: $225,000. Monthly payment: $1,422. Total interest: $287,014. Total cost: $512,014.

Example 2 — 15-year vs 30-year comparison: $300,000 home, 20% down ($60,000), 6% rate. 30-year: $1,439/month | Total interest: $278,011 15-year: $1,687/month | Total interest: $103,660 Choosing 15 years saves $174,351 in interest — at the cost of $248/month more.

Example 3 — Impact of down payment: $400,000 home at 6.5%, 30 years. 10% down ($40,000): payment $2,275/month | interest $458,880 20% down ($80,000): payment $2,022/month | interest $407,891 The extra $40,000 down saves $50,989 in interest and eliminates PMI.

A mortgage is almost certainly the largest financial commitment of your life. The difference between understanding your numbers and signing blindly can amount to hundreds of thousands of dollars over the life of the loan. Interest rate changes have an outsized impact: a 1% increase in mortgage rate on a $300,000 loan adds approximately $170 per month in payments and over $60,000 in total interest over 30 years.

Shopping multiple lenders and comparing rates is one of the highest-return financial activities available to a homebuyer. Research from the Consumer Financial Protection Bureau (CFPB) shows that borrowers who obtain at least three mortgage quotes save an average of $3,000 over the first five years — and significantly more over the full loan term. Even a 0.25% rate difference on a $400,000 loan saves over $18,000 over 30 years.

The loan term decision is equally consequential. A 15-year mortgage typically carries a 0.5–0.75% lower interest rate than a 30-year mortgage, and because of the shorter term, total interest paid is reduced by 50–60%. Financial planners generally recommend choosing the shortest loan term whose payments you can comfortably afford while still maintaining a 3–6 month emergency fund and contributing to retirement accounts.

This calculator computes the principal-and-interest (P&I) portion of your mortgage only. Your actual total monthly housing cost will be higher and includes items this calculator does not model: property taxes (typically 0.5–2.5% of home value per year, paid monthly into escrow), homeowner's insurance (typically $800–$2,000/year), private mortgage insurance (PMI, required when down payment is under 20%, costing 0.5–1.5% of the loan annually), and any homeowner association (HOA) fees.

This calculator also assumes a fixed interest rate for the full loan term. Adjustable-rate mortgages (ARMs) have rates that reset after an initial fixed period — typically 5, 7, or 10 years — which can cause payments to change significantly. This model does not account for refinancing, prepayments, or lump-sum principal paydowns, all of which can substantially reduce total interest paid.

Additionally, this calculator does not include closing costs, which typically run 2–5% of the purchase price and are due at the time of signing. For a $300,000 home, expect $6,000–$15,000 in closing costs. Factor this into your total upfront cash requirement alongside the down payment.