A $400,000 home loan at 7% over 30 years sounds manageable at $2,661 per month — until you realize you will pay a total of $558,036 by the time that loan is done. The extra $158,036 on top of what you borrowed? That is all interest. This mortgage calculator shows you exactly how that breaks down, month by month, so you can plan before you sign.
How Much Does a Mortgage Really Cost? (Real Examples)
The monthly payment is the number most buyers focus on. But the total interest paid over the loan's life is what separates a smart financial decision from a costly one. Here is what the same loan looks like across different amounts and terms at a 7% annual rate:
| Loan Amount |
Term |
Monthly Payment |
Total Interest |
Total Cost |
| $200,000 |
30 years |
$1,331 |
$279,018 |
$479,018 |
| $200,000 |
15 years |
$1,797 |
$123,497 |
$323,497 |
| $400,000 |
30 years |
$2,661 |
$558,036 |
$958,036 |
| $400,000 |
15 years |
$3,593 |
$246,988 |
$646,988 |
| $600,000 |
30 years |
$3,992 |
$837,054 |
$1,437,054 |
| $600,000 |
15 years |
$5,390 |
$370,484 |
$970,484 |
The pattern is consistent: a 15-year mortgage costs more each month but saves you an enormous amount in interest over the full loan life. On a $400,000 loan, you save $311,048 in interest by choosing the 15-year term — though your monthly payment rises by $932.
The Mortgage Formula (Explained With Real Numbers)
This calculator uses the standard amortizing mortgage formula:
M = P × [r(1+r)ⁿ] ÷ [(1+r)ⁿ−1]
Where:
- M = Monthly payment
- P = Loan amount (principal)
- r = Monthly interest rate = annual rate ÷ 12
- n = Total number of monthly payments = years × 12
Worked example: $300,000 loan at 6.5% for 30 years.
- r = 6.5% ÷ 12 = 0.5417% = 0.005417
- n = 30 × 12 = 360
- M = $300,000 × [0.005417 × (1.005417)³⁶⁰] ÷ [(1.005417)³⁶⁰ − 1]
- M = $1,896 per month
- Total paid = $682,632
- Total interest = $382,632
How to Use This Mortgage Calculator
- Enter the loan amount — the total you plan to borrow (not the home price; subtract your down payment).
- Enter the annual interest rate — use the rate quoted by your lender. If comparing scenarios, try several rates (e.g., 6%, 6.5%, 7%).
- Enter the loan term in years — typically 15 or 30 years for home loans.
- Click Calculate — your monthly payment, total interest, and total cost appear instantly.
- Download the CSV — export your complete amortization schedule showing every payment for the life of the loan.
Understanding the Amortization Schedule
An amortization schedule breaks down every monthly payment into two parts: how much goes toward principal and how much goes toward interest. The pattern is not intuitive until you see it.
On a 30-year loan, your early payments are almost entirely interest. In month 1 of a $300,000 loan at 7%, roughly $1,750 is interest and only $246 is principal. You will not reach the point where more than 50% of your payment goes to principal until approximately year 22.
This front-loading of interest is why mortgage refinancing can save you money even when the rate difference seems small. Refinancing early in a loan's life — before most of the interest has already been paid — has the greatest impact.
The first 12 months are shown in the table on this page. Click the download button to export the full schedule for all months.
15-Year vs 30-Year Mortgage: Which Should You Choose?
This is the most important decision for most mortgage borrowers. Here is the honest trade-off for a $300,000 loan at 7%:
| |
30-Year Fixed |
15-Year Fixed |
| Monthly payment |
$1,996 |
$2,696 |
| Total interest paid |
$418,527 |
$185,367 |
| Total cost of loan |
$718,527 |
$485,367 |
| Monthly payment difference |
— |
+$700/month |
| Interest savings |
— |
$233,160 |
Choose the 30-year if: the monthly payment difference would strain your budget, you plan to invest the savings aggressively elsewhere, or you expect your income to grow significantly.
Choose the 15-year if: you can comfortably afford the higher payment, you want to build equity faster, or you are closer to retirement and want the loan paid off sooner.
Pro tip: Run both scenarios in this calculator and look at the total interest column. The difference will often be more motivating than the monthly payment comparison alone.
What This Calculator Does NOT Include
This calculator computes principal and interest only. Your actual monthly housing cost will be higher. Budget for these additional expenses:
- Property taxes: Typically 0.5%–2% of your home's value per year, divided into monthly payments by most lenders. On a $400,000 home at 1.2%, that adds $400/month.
- Homeowner's insurance: Usually $100–$250/month depending on location and coverage.
- PMI (Private Mortgage Insurance): Required if your down payment is under 20%. Typically 0.5%–1.5% of the loan amount per year until you reach 20% equity.
- HOA fees: If applicable, add these separately.
A common rule of thumb is that your total housing costs should not exceed 28–30% of your gross monthly income.
Two Scenarios Where This Calculator Saves You Money
Scenario 1 — Checking your lender's quoted payment: Before signing any loan documents, enter the exact figures your lender gave you and compare the monthly payment. Lenders occasionally quote a rate and payment that do not match. If there is a discrepancy, ask your lender to explain it in writing.
Scenario 2 — Comparing loan terms before applying: Enter the same loan amount at different terms (10, 15, 20, 25, 30 years) and save the CSV for each. Total interest differences are often $150,000–$300,000 across common loan amounts. Seeing this in a spreadsheet before you commit changes how most buyers think about their loan term choice.
Frequently Asked Questions
How is the monthly mortgage payment calculated?
The calculator uses the standard mortgage amortization formula: M = P × [r(1+r)ⁿ] ÷ [(1+r)ⁿ−1], where P is the loan amount, r is the monthly interest rate (annual rate ÷ 12), and n is the total number of monthly payments. For a $300,000 loan at 7% over 30 years, that works out to $1,996 per month.
What is the difference between a 15-year and 30-year mortgage?
The monthly payment is higher on a 15-year mortgage, but the total interest paid is dramatically lower. On a $300,000 loan at 7%: the 30-year term costs $418,527 in total interest, while the 15-year term costs $185,367 — a savings of $233,160. Use this calculator to run both scenarios with your specific loan amount.
Does this calculator include property taxes and PMI?
No. This calculator covers principal and interest only. In practice, your total monthly housing payment will also include property taxes (typically 0.5%–2% of home value per year), homeowner's insurance, and PMI if your down payment is under 20%. Add those amounts to the calculated monthly payment for a complete budget picture.
What is a good mortgage interest rate right now?
Mortgage rates change frequently based on Federal Reserve policy and broader economic conditions. In 2024–2025, 30-year fixed rates in the US were generally in the 6.5%–7.5% range. Check current rates from your lender or a rate comparison site, then use this calculator to see exactly how different rates affect your monthly payment.
Can I download my full amortization schedule?
Yes. After calculating, click the Download CSV button to export your complete amortization schedule. The file includes every monthly payment showing principal paid, interest paid, and remaining loan balance — useful for budgeting and record-keeping.
Why does the amortization schedule preview only show 12 months?
The page preview shows the first 12 months to give you a clear picture of how your early payments are structured. Download the CSV to see the complete schedule for all months of the loan term.
What happens if the remaining balance shows zero in the last month?
This is correct. The final payment is automatically adjusted to clear any remaining balance that occurs due to rounding over the loan term. The last payment may be slightly different from earlier payments as a result.
