What is Mortgage Payment?
A mortgage payment is the monthly amount you pay to your lender covering principal, interest, property taxes, homeowners insurance, and (if applicable) PMI, collectively known as PITI. Understanding your monthly commitment is essential before committing to a home purchase. Use the Home Affordability Calculator to check what you can borrow, and the Closing Costs Calculator to estimate upfront costs.
The Formula
Monthly Payment = P × [r(1+r)^n] ÷ [(1+r)^n − 1]
P = principal (loan amount), r = monthly interest rate (annual rate ÷ 12), n = total number of monthly payments (term in years × 12). Add property tax/12, insurance/12, and PMI/12 for full PITI.
Worked Example
A $400,000 home in Austin, TX with $80,000 down (20%) gives a $320,000 mortgage at 6.75% over 30 years.
- Principal (P) = $320,000
- Monthly rate (r) = 6.75% ÷ 12 = 0.5625% = 0.005625
- Number of payments (n) = 30 × 12 = 360
- Monthly Payment = $320,000 × [0.005625 × 1.005625^360] ÷ [1.005625^360 − 1] = $2,076
- Total repaid = $2,076 × 360 = $747,360. Total interest = $427,360
📌 Principal and interest of $2,076/month over 30 years, with $427,360 in total interest, 134% of the original loan amount. Add roughly $500/month for Texas property tax and $150/month insurance to reach full PITI of $2,726.
Why This Matters
DTI qualification
Fannie Mae and Freddie Mac cap DTI at 45-50% for most loans; FHA allows up to 57% in strong files. On a $100,000 salary ($8,333/mo), your max PITI plus other debts is $3,750-$4,167. Calculate PITI with current rates before house hunting so you do not waste time on homes you cannot qualify for.
Term length trade-off
A 30-year term has payments roughly 40% lower than a 15-year, but you pay 2.2x more total interest. Use the calculator to compare 15-year and 30-year loans, most US buyers choose 30-year for flexibility and make voluntary extra payments.
Refinance timing
Freddie Mac estimates the average 30-year mortgage is refinanced or paid off within 7-10 years. Knowing your monthly payment at origination helps you model whether a future rate drop justifies the 1-2% refinance closing cost. A common rule of thumb is that a 0.75% or greater rate reduction with 5+ years remaining makes refinancing worthwhile.
Common Mistakes
❌ Forgetting PITI components
The P&I payment is not your full housing cost. Add property taxes (1.1% of value nationally, up to 2.5% in NJ/TX/IL), homeowners insurance ($1,500-3,500/year), HOA ($0-600/month), and PMI if under 20% down. Full PITI is typically 30-45% higher than P&I alone.
❌ Not stress-testing ARMs
If you take a 5/1 ARM at 5.75%, it can adjust up 2% per year and 5% over the life. A $320,000 loan could go from $1,867 to $2,587/month after the first adjustment. Always model the lifetime cap scenario.
❌ Ignoring the amortization front-loading of interest
In the first 5 years of a 30-year mortgage at 6.75%, roughly 80% of each payment goes to interest and only 20% to principal. Extra payments in the early years have an outsized effect on total interest paid. An extra $200/month from month one on a $320,000 loan saves over $90,000 in interest and shortens the term by about 7 years.
Industry Benchmarks
| Category | Good | Average | Poor |
|---|---|---|---|
| Housing payment as % of income | Below 28% | 28-36% | Above 36% |
| Total interest over term | Below 60% of principal | 60-100% | Above 100% |
| Loan-to-value ratio at origination | Below 80% (no PMI) | 80-95% | Above 95% |
Source: Freddie Mac PMMS & Fannie Mae Underwriting Guidelines
Benchmark data sourced from Freddie Mac PMMS & Fannie Mae Underwriting Guidelines.