The formula
M = P · r / (1 − (1 + r)^−n), where P is the loan amount, r is the monthly rate (annual / 12), and n is the number of months. It's exact algebra given the four inputs — the same formula Microsoft Excel's PMT() function uses.
Mortgage Calculator
Monthly payment, total interest, total paid — from the four numbers everyone has.
A fixed-rate mortgage is one of the most common loans on the planet, and the math is identical regardless of lender: monthly payment depends only on principal (home price minus down payment), interest rate, and term. The calculator below uses the textbook closed-form formula — no proprietary curve, no marketing adjustments. Property tax, HOA, and PMI are excluded on purpose so you can see the loan math cleanly.
Loan amount: $320,000.00
Monthly payment
$2,022.62
Total interest
$408,142.36
Total paid
$728,142.36
Principal & interest only. Property tax, homeowner’s insurance, HOA dues, and PMI are not included.
How to use
Enter price + down payment
Loan amount = home price minus down payment. Most US lenders require at least 3–20% down depending on loan type.
Enter rate and term
Use the rate you've been quoted (or the current national average — Freddie Mac's PMMS is the standard reference). 15- and 30-year are the common US terms.
Read the three numbers
Monthly payment is what you'll owe each month. Total interest is what the bank earns over the life of the loan. Total paid is principal + interest.
Quick reference
| Loan | Rate | Term | Monthly | Total interest |
|---|---|---|---|---|
| $200K | 6.0% | 30y | $1,199 | $231,676 |
| $200K | 6.0% | 15y | $1,688 | $103,788 |
| $400K | 6.5% | 30y | $2,528 | $510,178 |
| $400K | 5.5% | 30y | $2,271 | $417,615 |
Frequently asked questions
- What's included in the monthly payment?
- Principal and interest only. Property tax, homeowner's insurance, HOA dues, and PMI (if applicable) add to your real monthly housing cost. Most lenders escrow these — the figure on your closing disclosure (the PITI) is meaningfully higher than what this calculator shows.
- How does the interest rate affect the total?
- Hugely. A 1-percentage-point rate increase on a $400K / 30-year loan adds about $90K in total interest. Shaving the rate matters more than shaving the principal once you're inside the loan.
- Is a 15-year mortgage always better than 30-year?
- Lower lifetime interest, yes. But the monthly payment is meaningfully higher, and the cash you save on payments could potentially earn more invested. Run both with your real numbers.
- What about adjustable-rate or interest-only loans?
- Not yet — this calculator is for fixed-rate amortising loans only. ARM and IO calculators may follow.
- Does the calculator store my numbers?
- No. Everything stays in your browser. Convertitive doesn't have a backend you could even send loan data to.
About
What's not included
Property tax (highly local), homeowner's insurance (highly individual), HOA fees (highly community-specific), and PMI (depends on loan-to-value and lender). Add ~25-40% on top of the calculator's monthly payment as a rough first guess for the full PITI.