You find the house. You run the numbers. The listing says $450,000 and your bank says 6.75%. But what does that actually cost you every month? And over 30 years, how much do you really pay?
Most people sign a mortgage without ever seeing the full picture. They know the monthly payment. They don't know that on a 30-year loan, they'll pay almost as much in interest as the original price of the house.
Our Mortgage Calculator makes everything transparent — the monthly payment, the full amortization schedule, and exactly how much you save by paying extra each month. This guide explains how to use it and, more importantly, how to understand what the numbers mean.
How the Monthly Mortgage Payment Is Calculated
Every fixed-rate mortgage uses the same formula:
M = P × r(1+r)^n / ((1+r)^n − 1)
Where:
- M = monthly payment
- P = principal (loan amount after down payment)
- r = monthly interest rate (annual rate ÷ 12)
- n = total number of monthly payments (years × 12)
A Real Example
- Home price: $400,000
- Down payment: $80,000 (20%)
- Loan amount: $320,000
- Annual interest rate: 6.5%
- Term: 30 years
Monthly rate: 6.5% ÷ 12 = 0.5417% = 0.005417
Number of payments: 30 × 12 = 360
M = 320,000 × 0.005417(1.005417)^360 / ((1.005417)^360 − 1)
M ≈ $2,023/month
Total paid over 30 years: $2,023 × 360 = $728,280
Total interest paid: $728,280 − $320,000 = $408,280
That's right — you pay more in interest than the original loan principal. This is why understanding your amortization schedule changes everything.
What Is an Amortization Schedule?
An amortization schedule is a month-by-month breakdown of every payment across the life of the loan. For each payment, it shows:
- How much goes to principal (reduces your debt)
- How much goes to interest (goes to the bank)
- Your remaining balance after payment
The Shocking Front-Loading of Interest
In month 1 of the $320,000 loan above:
| Amount | |
|---|---|
| Total payment | $2,023 |
| Interest portion | $1,733 |
| Principal portion | $290 |
| Remaining balance | $319,710 |
You pay $2,023 and your balance drops by only $290. The bank gets $1,733.
By year 15 (halfway through the loan), the split flips:
| Amount | |
|---|---|
| Total payment | $2,023 |
| Interest portion | $991 |
| Principal portion | $1,032 |
| Remaining balance | $182,450 |
This is why early extra payments are so powerful — every dollar paid early eliminates a dollar of high-interest debt while the interest-to-principal ratio is at its worst.
How to Use the Mortgage Calculator
Step 1: Enter Your Loan Details
- Home Price — The purchase price of the property
- Down Payment — Toggle between dollar amount and percentage. 20% avoids PMI (private mortgage insurance) with most US lenders.
- Annual Interest Rate — Your quoted mortgage rate. Even a 0.5% difference changes the monthly payment by $100+ on a $300k loan.
- Term — Quick presets: 10, 15, 20, 25, or 30 years. Or type a custom term.
- Start Date — When your first payment is due (defaults to first of next month)
Step 2: Read the Summary Panel
Four key numbers appear immediately:
- Monthly Payment — Principal + interest only (not taxes, insurance, or PMI)
- Total Interest — What you pay the bank over the life of the loan
- Total Cost — Loan amount + total interest
- Payoff Date — The exact month and year you'll be debt-free
Step 3: Explore the Charts
Two visualizations come with every calculation:
Principal vs. Interest Pie Chart — Shows the total split between the amount you borrowed and what you pay in interest. On a 30-year loan at 6.5%, the pie is roughly 44% principal and 56% interest.
Balance Over Time Chart — A line chart showing how your balance drops over the loan term. Notice how it barely moves in the first five years — that's the front-loading effect at work.
Step 4: Review the Amortization Table
The full schedule shows every payment. Filter by year to see totals at a glance. Export to CSV if you want to run your own analysis in Excel or Sheets.
Extra Payments: Where the Real Savings Are
The extra payments section is the most powerful feature in the calculator. Here's what it can show you.
Monthly Extra Payments
Scenario: $320,000 loan, 6.5%, 30 years. Add $200/month extra.
| Standard | With $200/mo Extra | |
|---|---|---|
| Monthly payment | $2,023 | $2,223 |
| Payoff | Month 360 | Month 307 |
| Years saved | — | ~4.4 years |
| Total interest | $408,280 | $337,890 |
| Interest saved | — | $70,390 |
$200 extra per month saves $70,390 in interest. The return on that $200 is extraordinary because you're eliminating debt that carries a 6.5% guaranteed rate — better than most savings accounts.
One-Time Lump Sum
Coming into $20,000 (tax refund, bonus, inheritance)? Apply it in year 3:
| Without lump sum | With $20k lump sum in year 3 | |
|---|---|---|
| Total interest | $408,280 | $361,100 |
| Interest saved | — | $47,180 |
| Months saved | — | ~32 months |
A single $20,000 payment in year 3 saves $47,180 over the life of the loan — a 236% return on capital.
Combine Both
The calculator handles monthly extras and lump sums simultaneously. The amortization table updates to show both schedules — what you'd pay with just the standard payment vs. what the accelerated schedule looks like.
15-Year vs. 30-Year: Use Compare Mode
The Compare tab lets you run two scenarios side by side. Common use: same loan at different terms.
Same loan: $320,000 at 6.5%
| 30-Year | 15-Year | |
|---|---|---|
| Monthly payment | $2,023 | $2,791 |
| Total interest | $408,280 | $182,330 |
| Interest saved | — | $225,950 |
| Payoff | 2056 | 2041 |
A 15-year mortgage costs $768 more per month but saves $225,950 in interest and gets you debt-free 15 years earlier.
The question isn't whether the 15-year is mathematically better — it is. The question is whether the $768 monthly difference is sustainable for your cash flow, and what the opportunity cost is if you invested that difference instead.
The calculator shows you both schedules. You decide based on your situation.
Multi-Currency Support
The calculator supports USD, EUR, GBP, and ILS (Israeli Shekel). All numbers format correctly for your selected currency, and the display adapts for Hebrew (right-to-left).
Note for Israeli users: Israel uses a prime-rate plus spread system for variable mortgages. This calculator uses a flat rate — enter your current blended rate or expected fixed-rate portion as the annual rate.
Share Your Scenario
Every input you enter is reflected in the URL. Copy the URL from your browser to share your exact scenario — another person (or your future self) can open it and see the same numbers. Useful for comparing loan offers from different banks.
What the Calculator Doesn't Include
This calculator covers principal and interest (P&I) only. Your actual monthly payment to the lender will likely include:
- Property taxes — Escrowed monthly, typically 0.5–2% of home value annually
- Homeowners insurance — Escrowed monthly, typically $1,000–$3,000/year
- PMI (Private Mortgage Insurance) — Required if down payment is under 20%; typically 0.5–1.5% of the loan annually
- HOA fees — If applicable
Your lender's Loan Estimate (required within 3 business days of application) will show the full PITI amount (Principal, Interest, Taxes, Insurance).
Frequently Asked Questions
What's a good mortgage rate right now?
Rates change daily. Check current rates from multiple lenders before accepting an offer — even 0.25% makes a significant difference over 30 years.
Does a larger down payment lower my interest rate?
Not necessarily, but it reduces your loan amount, which directly reduces your total interest paid. A 20% down payment also eliminates PMI.
What if I make biweekly payments instead of monthly?
Biweekly means 26 half-payments per year = 13 full monthly payments instead of 12. That one extra payment per year on a 30-year loan typically saves 4–5 years and tens of thousands in interest.
Should I pay off my mortgage early or invest the extra money?
At current rates (6–7%), paying down your mortgage is a guaranteed 6–7% return. The S&P 500 has historically returned ~10% before inflation. The right answer depends on your risk tolerance and tax situation — our Compound Interest Calculator can help you model the investment side.
Can I use this for commercial real estate or car loans?
Yes — the underlying amortization math is identical. Enter the loan amount, rate, and term. The term for auto loans is typically 36–84 months (3–7 years).
Run your numbers in the Mortgage Calculator — it takes 30 seconds to see your full amortization schedule, and might change how you think about every payment you make.