What is the difference between 15 and 30-year mortgages?

A 15-year mortgage has higher monthly payments but lower total interest paid. A 30-year mortgage has lower monthly payments but you'll pay more interest over the life of the loan.

How much down payment do I need?

Conventional loans typically require 3-20% down. A 20% down payment helps you avoid Private Mortgage Insurance (PMI).

What factors affect my mortgage rate?

Credit score, down payment amount, loan term, loan type, and current market conditions all affect your mortgage interest rate.

Mortgage Calculator

A mortgage calculator can estimate monthly principal and interest from a home price, down payment, interest rate, and loan term, or work backward from a target

Mortgage Calculator Tool

Enter your values in the calculator above, then use the explanations below to understand the result, check assumptions, and compare scenarios.

About this calculator

A mortgage calculator can estimate monthly principal and interest from a home price, down payment, interest rate, and loan term, or work backward from a target monthly payment to estimate the mortgage principal that payment can support. The reverse calculation is useful when your budget starts with a monthly P&I ceiling rather than a purchase price. In either direction, the result covers loan principal and interest only; property taxes, homeowners insurance, mortgage insurance, HOA dues, closing costs, and lender qualification rules can materially change real-world affordability.

For a fixed-rate fully amortizing mortgage, the standard payment formula is P = L · (c·(1+c)^n) / ((1+c)^n − 1), where L is loan principal, c is the monthly interest rate, and n is the number of monthly payments. Monthly Payment mode solves this formula for P after subtracting the down payment from the home price. Loan Amount by Payment mode rearranges the same relationship to solve for L from a target P&I payment. This reverse result is a mortgage-principal estimate, not a home-price estimate or lender preapproval, because taxes, insurance, mortgage insurance, HOA dues, closing costs, income, credit, and other debts are outside the formula.

Use Monthly Payment mode when you know the home price and down payment. Use Loan Amount by Payment when you know the principal-and-interest payment you want to stay near. Compare multiple rates and terms because even modest rate changes can materially change either the payment on a fixed loan amount or the loan amount supported by a fixed payment. For a complete housing budget, add estimated taxes, insurance, mortgage insurance if applicable, HOA dues, and other recurring housing costs separately.

Worked examples

Standard 30-year fixed mortgage

Home price $400,000, 20% down ($80,000), 30-year fixed at 6.5% annual interest.

Loan principal L = $400,000 − $80,000 = $320,000
Monthly rate c = 0.065 / 12 ≈ 0.005417
Number of payments n = 30 × 12 = 360
Apply the fixed-rate amortization formula to solve for the monthly P&I payment

Result: The estimated monthly principal-and-interest payment is about $2,023. Taxes, insurance, mortgage insurance, and HOA dues are not included.

Solve for loan amount from a target payment

Target monthly P&I payment $2,500, 30-year term, 6.5% annual interest.

Monthly rate c = 0.065 / 12
Number of payments n = 360
Rearrange the amortization formula: L = P × (1 − (1+c)^−n) / c
Use $2,500 as the target principal-and-interest payment

Result: The reverse calculation estimates the mortgage principal supported by that payment. It does not by itself determine the home price or lender-approved amount.

Practical tips

Run several interest-rate scenarios instead of relying on one quote; the supported loan amount at a fixed payment falls as the rate rises.
Treat the reverse result as loan principal, not purchase price. Your down payment and transaction costs determine how that principal translates into a potential home price.
Add taxes, homeowners insurance, mortgage insurance, HOA dues, and other recurring housing costs before deciding whether a payment fits your budget.
Compare shorter and longer terms. A shorter term usually raises the monthly payment for the same principal but reduces total interest.
Use lender disclosures for a specific transaction because actual pricing, fees, qualification, and escrow amounts are outside this calculator.

Common mistakes

Treating principal-and-interest payment as the full monthly housing cost.
Treating the reverse loan-amount result as a lender preapproval or guaranteed purchase budget.
Comparing payment scenarios without keeping the interest rate and term assumptions consistent.
Ignoring the effect of a down payment when converting a loan amount into a possible home price.
Assuming a quoted interest rate will remain available until closing.

Key terms

Principal: The amount borrowed before interest. In reverse mode, this is the primary result the calculator estimates.
P&I: Principal and interest — the loan-payment components calculated by this tool.
PITI: Principal, interest, taxes, and insurance. This calculator estimates P&I, not the full PITI amount.
LTV: Loan-to-value ratio — loan principal divided by the property's value.
DTI: Debt-to-income ratio — monthly debt obligations compared with gross monthly income. This calculator does not perform lender qualification.
Amortization: The process of paying a loan down through scheduled payments that include both principal and interest.

Frequently asked questions

Can I calculate a mortgage loan amount from a monthly payment?: Yes. Select Loan Amount by Payment and enter a target monthly principal-and-interest payment, interest rate, and term. The calculator rearranges the fixed-rate amortization formula to estimate the mortgage principal supported by that payment.
Is the reverse result the home price I can afford?: No. It is an estimated mortgage principal. A possible purchase price also depends on your down payment, while actual affordability and lender approval depend on taxes, insurance, mortgage insurance, HOA dues, income, credit, other debts, and loan-program rules.
Does this calculator include property taxes and insurance?: No. The payment output is principal and interest only. Add property taxes, homeowners insurance, mortgage insurance if applicable, HOA dues, and other recurring housing costs separately.
How does my down payment change the payment?: In Monthly Payment mode, increasing the down payment reduces the financed principal dollar-for-dollar. With the same interest rate and term, a smaller principal produces a smaller principal-and-interest payment.
Why might my lender's payment differ from this calculator?: A lender may use a different rate or term and may include taxes, insurance, mortgage insurance, fees, escrow items, or other costs. Use the lender's official disclosures for the terms of a specific loan.