Mortgage Calculator
Estimate your monthly home loan payment, total interest and full amortization — free, instant, no sign-up.
Mortgage Payment Calculator
What this mortgage calculator does
Buying a home is almost certainly the largest financial commitment you will ever make, and the listing price tells you surprisingly little about what you will pay each month. This mortgage calculator converts three or four inputs — the loan amount, the annual interest rate, the loan term and an optional down payment — into the number that governs your budget: the monthly principal-and-interest payment.
Beyond the monthly figure, the tool shows the total amount you will repay over the entire loan and the portion of that total that is pure interest cost. On a typical $300,000 thirty-year mortgage at today's rates, the interest alone can exceed the original loan amount — so seeing that number before you sign can be clarifying, even sobering.
The calculator covers the core of any fixed-rate fully amortizing mortgage. It does not add property taxes, homeowners insurance, HOA fees or private mortgage insurance (PMI). Together those extras form what lenders call PITI; treat the result here as the loan portion of your payment and add your local estimates on top. Because the tool runs entirely in your browser, nothing you enter is stored or transmitted.
How to use it — step by step
- Enter the loan amount. If you already know the borrowed amount, type it directly. If you are starting from a purchase price, enter that price and add the down payment in the optional field below — the calculator will subtract it automatically.
- Enter the annual interest rate. Use the rate your lender quoted (the note rate, not APR). Try changing it in 0.25% increments to see exactly how sensitive your payment is to rate movement.
- Enter the term in years. The most common US mortgages are 30 or 15 years. A shorter term means a higher monthly payment but dramatically less total interest. You can enter any term, including 10, 20 or 25 years.
- Read the result. The monthly P&I payment, total repaid and total interest appear instantly. Change any input to compare scenarios side by side — 20% down vs. 10% down, 30 years vs. 15 years, or today's rate vs. a rate you could lock if you wait.
The formula explained
This calculator uses the standard fixed-rate amortization formula, which is used by every bank, mortgage broker and financial textbook in the world:
where P = loan principal · r = monthly interest rate (annual ÷ 12) · n = total payments (years × 12)
The formula produces a fixed payment that perfectly amortizes the loan: each month the interest due on the remaining balance is covered first, and the rest chips away at the principal. Because the balance shrinks every month, the interest portion of each payment shrinks too — so more and more of each fixed payment goes toward principal as time passes. This is why making extra payments early in a mortgage is so powerful: you eliminate future interest on every dollar of principal you pay off ahead of schedule.
If the interest rate is zero (for example, in a seller-financed arrangement), the formula degenerates to a simple division: monthly payment = principal ÷ number of payments.
Worked examples
Rate and term reference table
| Loan | Term | Rate | Monthly P&I | Total interest |
|---|---|---|---|---|
| $200,000 | 30 yr | 6.0% | $1,199 | $231,700 |
| $200,000 | 30 yr | 6.5% | $1,264 | $255,100 |
| $300,000 | 30 yr | 6.0% | $1,799 | $347,500 |
| $300,000 | 30 yr | 6.5% | $1,896 | $382,600 |
| $300,000 | 30 yr | 7.0% | $1,996 | $418,500 |
| $300,000 | 15 yr | 6.0% | $2,532 | $155,700 |
| $300,000 | 15 yr | 6.5% | $2,613 | $170,400 |
| $400,000 | 30 yr | 6.5% | $2,528 | $510,200 |
| $400,000 | 15 yr | 6.5% | $3,484 | $227,200 |
| $500,000 | 30 yr | 6.5% | $3,160 | $637,800 |
Principal and interest only. Taxes, insurance, HOA and PMI are not included. Figures rounded to nearest $100.
When to use a mortgage calculator
- Before house-hunting: Find the maximum loan amount that keeps the payment within your budget, so you only view homes you can realistically afford.
- Comparing lender offers: Plug in each lender's rate to see the real monthly and lifetime difference — a small rate gap can mean tens of thousands of dollars.
- Choosing between 15- and 30-year terms: Weigh the higher payment against the massive interest savings to decide which term fits your income and goals.
- Modeling different down payments: See how putting down 10%, 15% or 20% changes your loan amount and monthly payment.
- Refinancing decisions: Simulate a lower rate or shorter remaining term to decide whether the monthly savings justify the closing costs.
- Annual mortgage review: Check whether your current rate still makes sense compared to the market, especially after large payments of principal or significant equity gains.
Tips and common mistakes
Don't confuse the loan amount with the home price. The calculator works with what you are borrowing — always subtract your down payment first. Many first-time buyers accidentally enter the purchase price and are surprised by the payment.
Don't forget the extras. Property tax, homeowners insurance and PMI can add $400–$800 per month or more to the payment your lender quotes. Build those into your budget using local estimates before committing to a home price.
Watch the term, not just the rate. Accepting a higher rate in exchange for a shorter term can still save money. Run both scenarios in the calculator before deciding.
ARMs need a different approach. An adjustable-rate mortgage fixes the payment only for the introductory period (typically 5 or 7 years). After that, the rate adjusts annually. This calculator assumes the rate stays constant, so use it for the fixed-rate phase of an ARM or for fixed-rate loans only.
Extra payments are powerful early. Every additional dollar you pay toward principal in the first years eliminates years of future interest. Even an extra $100 a month on a $300,000 30-year loan at 6.5% can shave more than 4 years off the term and save over $60,000 in interest.
Frequently asked questions
How is the monthly mortgage payment calculated?
The calculator uses the standard amortization formula: M = P·r·(1+r)ⁿ / ((1+r)ⁿ−1), where P is the loan principal, r is the monthly interest rate (annual rate ÷ 12), and n is the total number of monthly payments (years × 12). Each payment first covers the interest due for that month; the remainder reduces the outstanding principal.
Does this calculator include property tax and insurance?
No. It shows only principal and interest (P&I). Your total monthly housing cost will also include property taxes, homeowners insurance, HOA fees and, if your down payment is under 20%, private mortgage insurance (PMI). Add those figures from your lender or local records to get the complete monthly obligation.
Is a 15-year or 30-year mortgage better?
A 15-year loan carries a higher monthly payment but dramatically less total interest — often over $200,000 less on a $300,000 mortgage. A 30-year loan keeps monthly payments lower and is easier to manage on a tight budget, but you pay far more interest over time. The best choice depends on the payment you can comfortably sustain, your job security and how much the interest savings matter to you long-term.
How much does a lower interest rate save?
On a $300,000 30-year loan, dropping from 6.5% to 5.5% lowers the monthly payment by about $193 and saves roughly $69,500 in total interest. Even a quarter-point difference — 6.5% vs. 6.25% — saves about $17,500 in total interest and roughly $49 per month. Shopping multiple lenders before signing is almost always worthwhile.
What is amortization and how does it work?
Amortization is the process of paying off a debt through regular equal payments over time. For a fixed-rate mortgage, each monthly payment is the same dollar amount, but the split between interest and principal shifts throughout the loan. Early on, most of your payment covers interest. As the principal balance falls, the interest charge shrinks and more of each payment pays down the balance. An amortization schedule lists every single payment over the loan's life, showing exactly how much goes to interest versus principal each month.
Can I see the effect of extra payments?
Yes, indirectly. Lower the entered loan amount (simulating a lump-sum extra payment) or shorten the term to see how the payment and total interest change. Any extra principal payment reduces the balance that interest is calculated on in every subsequent month, which shortens the effective loan and cuts total interest significantly. For detailed extra-payment analysis, see our Loan Payoff Calculator.
What is PMI and should I avoid it?
Private mortgage insurance (PMI) is a monthly premium your lender charges when your down payment is less than 20% of the home price — typically 0.5%–1.5% of the loan amount per year. It protects the lender if you default, not you. PMI is not included in this calculator. Once you reach 20% equity, you can typically request PMI removal, saving hundreds of dollars per month.
What is the difference between interest rate and APR?
The interest rate is the annual cost of borrowing the principal — the number used in the amortization formula. APR (Annual Percentage Rate) is broader: it includes the interest rate plus origination fees, discount points and other lender costs, expressed as a yearly rate. APR makes it easier to compare loan offers from different lenders. This calculator uses the note rate (interest rate), not APR.
How do I know how much mortgage I can afford?
A common guideline is that your total housing payment (P&I plus taxes, insurance and HOA) should not exceed 28% of your gross monthly income, and your total monthly debt payments should stay below 36–43%. Use this calculator to find a payment that fits, then work backward to the maximum loan amount. Lenders will also evaluate your credit score, debt-to-income ratio and down payment when deciding how much to lend.
Should I choose a fixed-rate or adjustable-rate mortgage?
A fixed-rate mortgage locks your interest rate for the entire loan term, so your P&I payment never changes — ideal if you plan to stay in the home long-term or rates are currently favorable. An adjustable-rate mortgage (ARM) offers a lower initial rate for a set period (e.g., 5 or 7 years), then adjusts annually based on a market index. ARMs can be cheaper if you plan to sell or refinance before the adjustment period. This calculator assumes a fixed rate throughout.