Mortgage Down Payment and Monthly Payment Calculator

How the calculation works

Mortgage Down Payment: Loan Amount, LTV and Monthly Payment

When you compare home loans, the purchase price is only the starting point. The amount the lender actually finances depends on the down payment, which is the cash the buyer puts into the purchase without borrowing it. This calculator starts from the purchase price and the down payment to determine three figures that appear in every mortgage offer: the loan amount, the loan-to-value ratio (LTV) and the estimated monthly payment. The formula contains no physical units, so there is no metric-to-imperial conversion to apply: enter the price, the down payment and the rate as they appear in your offer.

How the loan amount is worked out

The loan amount is the purchase price minus the down payment. The lender does not finance the full price of the home. It finances only the part the buyer cannot cover with their own funds. The calculator requires the down payment to be lower than the price. If the down payment equals or exceeds the price, there is no loan to finance, and the calculator shows no result.

If the lender uses an appraisal to set the value of the home, an appraisal below the agreed price changes the LTV and can reduce the loan the lender is willing to make, even when the buyer has saved the planned down payment. Ask the lender which value it will use for the loan, and build a margin for this possibility when you set the amount to put down.

What the LTV tells the lender

The LTV is the loan amount divided by the value of the home, expressed as a percentage. A down payment of 20% of the price gives an LTV of 80%. A lower LTV means less risk for the lender, because the borrower has more of their own money at stake and there is more equity to protect the loan if the property value falls.

In the United States, LTV affects more than the approval decision. Conventional loans with a loan-to-value above 80% usually require private mortgage insurance, which protects the lender if the borrower defaults. The Homeowners Protection Act of 1998 sets rules for when that insurance can be canceled, using 80% of the original value as a key reference point. Government-backed programs, such as loans insured by the Federal Housing Administration, have their own rules for down payments and mortgage insurance, so the LTV that matters depends on the loan type.

Lenders also use LTV when they set pricing. Within the same loan program, a lower LTV often supports a better rate, which lowers the monthly payment and the total interest. The exact pricing grid belongs to each lender, so compare offers directly rather than relying on a single rule of thumb.

How the monthly payment is calculated

The monthly payment in this calculator uses the level-payment amortization method, which gives a fixed payment for the whole term of a fixed-rate loan. Each month the borrower pays the same amount, and that payment covers the interest accrued in the month plus a portion of the principal. Early in the loan, most of each payment is interest. Over time, the principal share grows until the balance reaches zero at the end of the term.

Three inputs determine the payment: the loan amount, the monthly interest rate and the number of payments. The number of payments equals the term in years multiplied by 12, so a 30-year term produces 360 monthly payments. The formula requires the number of payments to be greater than zero.

The formula also has a special case. If the interest rate is zero, the payment is simply the loan amount divided by the number of payments, because no interest accrues. The calculator handles this case, but a zero rate is rare in practice and usually appears only in promotional or family arrangements.

Index rate, spread and the nominal rate

The interest rate in the calculator is the nominal annual rate, labeled NR. It is the sum of an index rate and a spread. The index rate is the benchmark that moves with market conditions. In the United States, adjustable-rate loans commonly reference SOFR, the Secured Overnight Financing Rate published by the Federal Reserve Bank of New York, and some reference the Prime Rate. The spread, or margin, is the amount the lender adds on top of the index to cover its costs and profit and to reflect the borrower's risk profile.

For a fixed-rate mortgage, the rate in the offer is fixed for the whole term, and the spread is built into it. For an adjustable-rate mortgage, the index changes after an initial fixed period, and the payment can change with it. This calculator assumes the rate stays constant for the whole term. It does not model rate adjustments, rate caps or interest-only periods, so use it to estimate a fixed-rate scenario or a single rate assumption.

The Consumer Financial Protection Bureau (CFPB) publishes consumer guidance on mortgage terms and disclosures, and the Federal Reserve Bank of New York publishes SOFR data. Both are useful references when you want to check the index that applies to a specific loan.

How the down payment and term change the payment

A larger down payment reduces the loan amount, which reduces the monthly payment for the same term and rate. Because the payment is calculated on the loan amount, the effect is direct and proportional. A smaller loan also means less total interest over the life of the loan.

The term has an even larger effect on total cost. A longer term lowers the monthly payment, but it increases the total interest, since the balance stays outstanding for more months. Use the calculator to compare, for example, a 15-year and a 30-year term at the same price, down payment and rate. The monthly payment will be higher on the shorter term, while the total interest will be considerably lower.

A practical method is to test three or four down payment levels at the same price and term, and note the LTV, the monthly payment and the total interest for each. The comparison shows where the mortgage insurance threshold falls and how much each additional increment of the down payment changes the payment.

Closing costs and cash needed at closing

The down payment is not the only cash a buyer needs. The LTV and the monthly payment do not include closing costs, which are paid separately at settlement. These typically cover lender fees, an appraisal, a title search and title insurance, recording fees and, depending on the state, transfer taxes or other charges. Property taxes and homeowners insurance are usually collected through an escrow account and added to the monthly housing cost, but they are not part of the principal and interest payment shown here.

Because closing costs come from savings, planning should cover both the down payment and these costs. Buyers who plan a purchase with only the down payment in mind often find they have less cash available than expected. The Loan Estimate, the standard form lenders provide after an application under CFPB rules, lists the expected closing costs and the projected monthly payment. Compare that document with the result from this calculator, and treat the calculator as a first estimate.

Prepayments and simulating a partial paydown

Many borrowers make extra payments or pay down part of their balance. A partial prepayment reduces the principal, and depending on how the lender applies it, it can lower the monthly payment or shorten the remaining term. Federal rules under Regulation Z restrict prepayment penalties on many residential mortgages, but the loan documents set out whether a penalty applies, so check them before you pay ahead.

To simulate a partial prepayment, enter the remaining balance as the purchase price, enter zero as the down payment, and set the term to the number of years left on the loan. The calculator then shows the estimated monthly payment for the new balance. The LTV will show 100%, which is a side effect of the method and can be ignored in this case. Compare the new payment with the current one to see the effect of the prepayment.

Nominal rate versus APR

The nominal rate in this calculator is not the same as the annual percentage rate (APR) shown in US loan disclosures. The APR is calculated under the Truth in Lending Act and Regulation Z, and it includes certain finance charges and fees in addition to the interest rate. A loan with a lower nominal rate can have a higher APR if it charges larger upfront fees, which is why comparing offers on the nominal rate alone can be misleading.

For this reason, use this calculator to understand the mechanics of the loan and to test scenarios, then compare final offers using the APR printed in the disclosures. The calculator does not compute the APR, and it does not replace the disclosure documents that the lender provides.

Edge cases and limits of this calculator

The result is a mathematical estimate based on the inputs. It does not include property taxes, homeowners insurance, mortgage insurance premiums, homeowners association dues, closing costs or any change in the rate over time. It also does not check credit eligibility, debt-to-income limits or underwriting standards, all of which determine whether a loan is approved.

Several situations need special care. Very short terms and high rates produce large payments that may be hard to sustain over time. A very small or zero down payment pushes the LTV close to 100%, which usually means mortgage insurance and a narrower range of loan programs. When the down payment equals or exceeds the price, no loan is needed and the calculator shows no result. Lenders usually offer terms in whole years, so enter whole numbers unless your offer uses a different schedule.

When to speak to a professional

A mortgage broker licensed in your state can compare offers from several lenders, which saves time. A broker is useful when your credit history has gaps, when your income is irregular, as it can be for self-employed people, or when your situation includes co-borrowers, gift funds or non-standard income. Ask how the broker is paid, since compensation can come from the lender or from the borrower. The Nationwide Multistate Licensing System, known as NMLS, provides a public register of licensed mortgage professionals that you can search before you hire one.