How to Calculate Your Monthly Mortgage Payment — Free Calculator + Formula
Understanding your mortgage payment is one of the most important calculations most people will ever make. A house is likely the largest purchase of your life — yet most buyers simply accept the number their bank gives them without understanding where it comes from or what changes it.
This guide explains exactly how mortgage payments are calculated (with the real formula, in plain English), shows you how to use our free calculator, and reveals the single most powerful action you can take to save tens of thousands in interest: extra payments.
This article is educational and not financial advice. For decisions about a specific loan, consult a licensed mortgage professional or financial advisor.
The Short Answer — Use the Calculator First
If you want the number fast, our free mortgage calculator gives you your monthly payment, total interest paid, and a full amortization schedule in seconds. No account, no ads in the way, no personal data collected.
Enter your home price, down payment (amount or percentage), annual interest rate, and loan term (15 or 30 years are most common). The calculator shows your monthly payment, total amount paid, total interest paid, and an amortization schedule showing exactly how much of each payment goes to principal vs. interest.
The Mortgage Payment Formula Explained
The mathematical formula for a fixed-rate monthly mortgage payment is:
M = P × [r(1+r)^n] / [(1+r)^n - 1]
Where M is the monthly payment, P is the principal loan amount (home price minus down payment), r is the monthly interest rate (annual rate ÷ 12), and n is the total number of payments (years × 12).
Example — $400,000 loan, 6.5% annual rate, 30-year term:
P = $400,000
r = 6.5% ÷ 12 = 0.005417
n = 30 × 12 = 360 payments
M = 400,000 × [0.005417 × (1.005417)^360] / [(1.005417)^360 - 1]
M ≈ $2,528 per month
Total paid over 30 years: $2,528 × 360 = $910,080. Total interest paid: $510,080 — more than the original loan amount paid in interest alone. This is why understanding your mortgage, and the power of extra payments, matters so much.
What Your Monthly Payment Actually Covers
The payment calculated by the formula covers principal and interest only (P&I). Your actual monthly payment to your lender is typically higher because it includes the four components known as PITI: Principal (the portion that reduces your loan balance), Interest (the cost of borrowing), Taxes (property taxes collected monthly and held in escrow), and Insurance (homeowner's insurance, also escrowed). If your down payment is less than 20%, private mortgage insurance (PMI) is added until your loan-to-value ratio drops below 80%.
Example — $400,000 home, $80,000 down (20%), 6.5% rate:
| Component | Monthly amount |
|---|---|
| Principal & Interest | $2,024 |
| Property tax (~1.2% annual) | $400 |
| Homeowner's insurance | $100 |
| PMI (not applicable, 20% down) | $0 |
| Total monthly payment | $2,524 |
The P&I portion stays constant for the life of a fixed-rate mortgage. Taxes and insurance can change year to year.
How Amortization Works — Why Early Payments Are Mostly Interest
"Amortization" means paying off a loan with regular payments. The key insight is that the split between principal and interest changes dramatically over the loan's life. With a $320,000 loan at 6.5% for 30 years (monthly payment $2,024):
| Payment | Principal paid | Interest paid | Remaining balance |
|---|---|---|---|
| Month 1 | $290 | $1,733 | $319,710 |
| Month 60 (Year 5) | $352 | $1,672 | $303,460 |
| Month 180 (Year 15) | $474 | $1,550 | $271,378 |
| Month 300 (Year 25) | $638 | $1,386 | $221,359 |
| Month 360 (Year 30) | $740 | $1,284 | $0 |
In month 1, only $290 of your $2,024 payment reduces the loan balance — $1,733 is pure interest. You're over halfway through the loan before you've paid off even 15% of the principal. This is why the first few years of a mortgage are the most powerful time to make extra payments.
15-Year vs. 30-Year Mortgage — The Real Numbers
The most common mortgage decision is the loan term. Here's the comparison for a $320,000 loan at 6.5%:
| 30-Year | 15-Year | |
|---|---|---|
| Monthly P&I payment | $2,024 | $2,790 |
| Total paid | $728,640 | $502,200 |
| Total interest paid | $408,640 | $182,200 |
| Interest saved | — | $226,440 |
A 15-year mortgage saves $226,440 in interest — more than 70% of the original loan amount. The trade-off is $766 more per month. The right choice depends on your income stability, other financial goals, and risk tolerance. A common suggestion: if you can't comfortably afford the 15-year payment, get the 30-year but make extra payments when possible.
The Power of Extra Payments — The Most Important Section
Making even modest additional principal payments early has a dramatic compounding effect. Because interest is calculated on the remaining balance, every dollar of principal you pay early eliminates all the interest that dollar would have accumulated over the remaining loan life.
Example: $320,000 loan, 6.5%, 30-year term, $2,024/month
| Extra payment | Loan paid off | Years saved | Interest saved |
|---|---|---|---|
| None | 30 years | — | — |
| $100/month extra | 26 yr 8 mo | 3 yr 4 mo | $48,723 |
| $200/month extra | 24 yr 3 mo | 5 yr 9 mo | $83,151 |
| $500/month extra | 19 yr 11 mo | 10 yr 1 mo | $150,274 |
| $1,000/month extra | 16 yr 1 mo | 13 yr 11 mo | $196,421 |
$100 extra per month saves you $48,723 and almost 3.5 years. To apply extra payments: make your regular payment as usual, send an additional payment, and critically — specify that the extra amount should be applied to principal only, not to the next month's payment. If applied to the next month's payment, you don't save interest. Our mortgage calculator has an "extra payment" field showing exactly how many months you save.
What Interest Rate Do You Qualify For?
The interest rate is the most impactful variable. Impact on a $320,000, 30-year mortgage:
| Rate | Monthly payment | Total interest |
|---|---|---|
| 5.0% | $1,718 | $298,480 |
| 6.0% | $1,919 | $370,840 |
| 6.5% | $2,024 | $408,640 |
| 7.0% | $2,129 | $446,440 |
| 7.5% | $2,237 | $484,920 |
A 1% difference in rate is $105/month and $74,000+ over 30 years on this loan size. Factors that determine your rate include credit score (the single most impactful factor), loan-to-value ratio, loan type, loan term, market conditions, and lender competition — getting quotes from 3–5 lenders typically saves 0.25–0.5% vs. accepting the first offer.
How Much Mortgage Can You Afford?
The most common guideline is the 28/36 Rule: monthly housing costs (PITI) should not exceed 28% of gross monthly income, and total debt payments should not exceed 36%. For a $7,000/month gross income, that's a maximum housing payment of $1,960 and maximum total debt of $2,520. If you have $600/month in other debt, your maximum housing payment is $1,920.
Another rough guideline: your mortgage should be no more than 2–3× your annual gross income. Our calculator also works in reverse — enter a comfortable monthly payment and adjust the home price until it matches.
Frequently Asked Questions
What is included in a mortgage payment? The base calculation covers principal and interest (P&I). Your actual payment typically also includes property tax and homeowner's insurance held in escrow (PITI), plus PMI if your down payment is under 20%.
How do I calculate my mortgage payment manually? Use the formula M = P × [r(1+r)^n] / [(1+r)^n - 1], where P is the loan amount, r is the monthly rate (annual ÷ 12), and n is the total number of payments. Or use our free calculator for instant results.
What credit score do I need for a mortgage? Most conventional lenders require a minimum of 620. FHA loans allow scores as low as 500 (with 10% down) or 580 (with 3.5% down). The best rates go to borrowers above 740–760.
Is it worth making extra mortgage payments? Almost always yes, especially in the first 10 years. Extra payments applied to principal save the full remaining interest on that amount — the earlier you pay, the more you save.
What happens if I miss a mortgage payment? Most lenders have a 15-day grace period before a late fee. After 30 days, the missed payment may be reported to credit bureaus. After 90–120 days, lenders typically begin foreclosure. Contact your lender immediately if you anticipate difficulty — most have hardship programs.