Mortgage Calculator

A mortgage is a secured loan taken out to purchase real estate, with the property itself serving as collateral for the lender. The lender — typically a bank, credit union, or mortgage company — provides the capital needed to buy the home, and the borrower agrees to repay that amount plus interest over a fixed period through regular monthly payments. If the borrower fails to keep up with payments, the lender has the legal right to foreclose on the property and sell it to recover what is owed.

Each monthly mortgage payment covers two components: interest and principal. Interest is the cost the lender charges for lending you money, calculated as a percentage of the outstanding loan balance. Principal is the portion that actually reduces the amount you owe. In the early years of a mortgage, the vast majority of each payment goes toward interest, with only a small slice reducing the principal balance. Over time, as the balance decreases, this ratio gradually shifts in your favor — a process called amortization.

Standard mortgage terms are 15 and 30 years, though 10- and 20-year options also exist. A 30-year mortgage offers a lower monthly payment because the debt is spread over more time, but the total interest cost is substantially higher. A 15-year mortgage requires a larger monthly payment but builds equity faster and costs far less overall. For example, on a $300,000 loan at 7%, a 30-year term results in roughly $419,000 in total interest, while a 15-year term at the same rate costs around $185,000 — a difference of over $234,000.

Mortgage payments are calculated using a standard amortization formula: M = P × [r(1+r)^n] / [(1+r)^n − 1]. In this formula, M is the monthly payment, P is the loan principal (the amount borrowed), r is the monthly interest rate (the annual rate divided by 12), and n is the total number of monthly payments (the loan term in years multiplied by 12). This formula produces a fixed payment that stays the same every month while the split between interest and principal gradually changes.

As a concrete example, take a $300,000 loan at a 7% annual interest rate over a 30-year term. The monthly rate r = 7% ÷ 12 = 0.5833%. The total number of payments n = 30 × 12 = 360. Applying the formula gives a monthly payment of $1,996. Over the full 30 years, you will make 360 payments totalling approximately $718,760, meaning the total interest paid is about $418,760.

Breaking down the very first payment illustrates how amortization works in practice. Month 1 interest = $300,000 × (7% ÷ 12) = $1,750. Principal reduction = $1,996 − $1,750 = $246. After that first payment, the outstanding balance drops to $299,754. The following month, interest is calculated on the slightly smaller balance, so a marginally larger portion of the $1,996 goes toward principal. This shift accelerates every month until by the final payment, almost the entire $1,996 retires the last sliver of principal.

A fixed-rate mortgage locks in the same interest rate for the entire loan term. Your monthly principal and interest payment never changes regardless of what happens to interest rates in the broader economy. This predictability makes fixed-rate mortgages the most popular choice for buyers who plan to stay in their home long term and want to budget with certainty. Fixed rates are especially attractive when market rates are low, since you lock in a favorable cost for decades.

An adjustable-rate mortgage (ARM) has an initial fixed period — commonly 5, 7, or 10 years — during which the rate stays constant, followed by periodic adjustments based on a market benchmark index plus a lender margin. ARMs are often offered at lower initial rates than comparable fixed-rate products, which can mean meaningful savings during the fixed period for buyers who plan to sell or refinance before the adjustment begins.

The primary risk of an ARM is rate shock when the adjustment period begins. A 5/1 ARM that starts at 5.5% could adjust to 7.5% or beyond when the fixed period ends, adding hundreds of dollars to the monthly payment with little warning. Lenders are required to disclose adjustment caps — limits on how much the rate can rise per adjustment and over the life of the loan — but even capped ARMs can become significantly more expensive. ARMs are best suited for buyers with a clear, short-term plan for the property and a high tolerance for payment variability.

Property taxes are levied by local governments and can add anywhere from $100 to over $1,500 per month to your housing cost depending on your location and assessed property value. Most lenders require monthly tax contributions to be collected alongside your mortgage payment and held in an escrow account, from which the lender pays your tax bill when it comes due. This ensures the lender's collateral is protected from tax liens.

Homeowners insurance is also typically required by lenders as a condition of the loan and covers losses from fire, storms, theft, and other covered perils. Premiums vary widely but commonly run $100 to $200 per month. In planned communities and condominium developments, Homeowners Association (HOA) fees add another layer of monthly expense — often $100 to $500 or more — covering shared amenities and exterior maintenance.

Private Mortgage Insurance (PMI) applies when your down payment is less than 20% of the purchase price, meaning your loan-to-value (LTV) ratio exceeds 80%. PMI protects the lender — not you — against default risk and typically costs 0.5% to 1.5% of the loan amount per year. On a $300,000 loan, that translates to $1,500 to $4,500 annually, or $125 to $375 per month. The silver lining is that PMI is not permanent: once your equity reaches 20% through payments and/or appreciation, you can request cancellation. Taken together, all these components — Principal, Interest, Taxes, and Insurance — are known as PITI, which represents your true monthly housing cost.

Making extra principal payments is the most straightforward acceleration strategy. Even a modest additional $100 per month on a $300,000, 30-year mortgage at 7% reduces the loan term by approximately 4 years and eliminates over $51,000 in total interest — more than 10% of the original loan amount. You can direct extra payments monthly, quarterly, or as a one-time lump sum; just instruct your lender in writing to apply the additional amount to principal rather than prepaid interest.

Switching to biweekly payments is another low-effort strategy with meaningful results. Instead of making 12 full monthly payments per year, you make 26 half-payments — the equivalent of 13 full payments annually. That one extra payment each year chips away at the principal faster, shaving roughly 4 to 5 years off a standard 30-year mortgage and saving tens of thousands in interest. Many lenders offer biweekly payment programs, though some charge a setup fee — check the math to ensure the savings outweigh any cost.

Refinancing to a lower rate or shorter term can also generate substantial savings. If market rates have fallen since you took out your mortgage, refinancing can reduce your monthly payment or — if you keep the same payment and shorten the term — slash the total interest dramatically. Always calculate the break-even point before refinancing: divide the total closing costs (typically 2% to 5% of the loan amount) by the monthly savings the new loan produces. If you plan to remain in the home past that break-even date, refinancing usually makes strong financial sense.