Last updated: 2026-05-08

Total monthly housing cost

A mortgage payment is the recurring sum a borrower pays to carry a home loan. The figure lenders quote covers only principal and interest, but the full out-of-pocket cost also includes property tax, home insurance, and — when the down payment is under 20% — private mortgage insurance (PMI). The combination is commonly abbreviated PITI: principal, interest, taxes, insurance. This calculator shows the full PITI + PMI breakdown alongside a live amortization curve, and computes how much interest and how many months an extra monthly payment removes. It defaults to a 30-year fixed-rate mortgage.

Monthly principal and interest

Principal and interest (P&I) is the contractual portion of the payment — the amount that retires the loan over its term. It follows the standard PMT formula, the same one a spreadsheet uses:

Here L is the loan amount, r the annual interest rate (e.g. 0.065 for 6.5%), and n the total number of months (term × 12). On a $300,000 loan at 6.5% for 30 years, this is $1,896.20 per month. The monthly rate r/12 and the monthly compounding count n are the fixed-rate convention; an annual rate is divided by 12 to apply once per scheduled payment.

The PITI components

Three escrow items sit on top of P&I:

• Property tax is billed annually but typically escrowed monthly into the payment by the lender. Rates vary by state — roughly 0.5–2.5% of home value, with Texas, New Jersey, and Illinois at the high end and Hawaii, Alabama, and Colorado at the low end.
• Home insurance is required by lenders for any financed purchase. High-risk areas (hurricane corridors, wildfire-prone counties, flood plains) can run several times the national average and are increasingly difficult to insure outright.
• PMI applies to conventional loans when the loan-to-value ratio (LTV) exceeds 80%. Typical rates run 0.3–1.5% of the loan annually. PMI auto-cancels at 78% LTV under federal law (the Homeowners Protection Act) and can be requested at 80%.

The calculator sums all four into a single total monthly payment. Measured against gross monthly income, under 28% on housing alone is the conventional comfort threshold.

Amortization

After each payment, part covers interest and part reduces principal. Early in the loan most of the payment is interest; over time the proportion reverses as the balance shrinks. The remaining balance at month m has a closed form:

where PMT_eff = P&I + any extra monthly payment. The amortization chart sweeps m across the loan term and plots three curves: remaining balance, cumulative principal paid, and cumulative interest paid.

Extra-payment payoff

An extra monthly payment goes entirely to principal, which shortens the term. The closed-form payoff month is:

When the extra is zero, this reduces to the original term. When it is positive, n* arrives earlier, and the interest on every month no longer paid is avoided. Because a dollar of principal retired early removes all the interest that dollar would have accrued over the remaining term, even modest extras accumulate substantial savings.

Worked example

On a $300,000 home with a 30-year 6.5% loan, comparing the same rate across two terms shows the lifetime-interest difference:

• $300k @ 6.5% × 30y → $382k interest, $1,896/mo P&I
• $300k @ 6.5% × 15y → $170k interest, $2,613/mo P&I

The 15-year term costs $212k less in interest but adds $717 to the monthly payment. Adding $200/month to the 30-year loan instead pays it off about 6 years 2 months earlier and saves roughly $108k in lifetime interest — an effective return of 6.5%, fixed and free of market risk.

Variations and exclusions

• Adjustable-rate mortgages (ARMs): the model assumes a fixed rate. For an ARM, the current rate gives today's payment; re-running with the lifetime cap (typically the start rate plus 5–6 percentage points) shows the stress-test ceiling. The amortization shape changes once the rate adjusts.
• Closing costs (typically 2–5% of the loan) are excluded and should be budgeted separately.
• HOA fees, maintenance, and repair reserves: a 1–2% annual maintenance reserve on home value is a common planning figure.
• Tax benefits: the mortgage interest deduction (subject to the $750k cap and the itemization-versus-standard-deduction trade-off) and the points deduction are post-tax effects, not modeled here.
• Biweekly schedules, balloon payments, and graduated-payment programs use different math.
• Refinancing: modeling a refi means running two separate scenarios and comparing the break-even.

Applying the result

The all-in PITI figure, not the headline P&I, is the number that reflects actual cash flow. On a $300k home in Texas (2.0% property tax) with $1,500/yr insurance and a 10% down payment (PMI ~0.5%), the all-in monthly is ~$2,512 — about 32% higher than the $1,896 P&I. Underwriting may approve a loan that strains the monthly budget, so the PITI total is the more relevant constraint for planning.

To work the question from the income side instead — what loan size keeps the debt-to-income ratio below a target given a salary — see the Mortgage Affordability Calculator, which computes the maximum loan amount for a given income, rate, and term.

A few common decisions follow from the same model. Choosing a 15-year over a 30-year term roughly halves lifetime interest at the cost of a higher monthly payment; the trade-off worsens if the higher payment crowds out retirement contributions or an employer 401(k) match. Extra principal payments and a re-appraisal after local prices rise are the two routes to reaching 80% LTV sooner and ending PMI, which typically costs $50–$150/month. A refinance becomes worthwhile when the monthly savings recover the closing costs (2–5% of the new loan) before the home is sold — running the current loan and a hypothetical refi side by side gives the break-even month.

This calculator provides a clean, realistic baseline for the structural cost of the loan. Specific lender quotes, tax brackets, and personal circumstances should be layered in when finalizing a decision.