Methodology

How TruePITI calculates, what we assume, where data comes from, and how we keep it current. Last updated: 2026-09-17.

Mortgage Payment (P&I) Formula

Monthly principal + interest uses the standard amortization formula:

P = L × [r(1+r)ⁿ] / [(1+r)ⁿ − 1]
where L = loan amount, r = annual rate ÷ 12, n = months

The amortization schedule is generated month by month from this formula — interest = current balance × r, principal = payment − interest. Balance shown after each year in the schedule table.

PITI Components

Property tax: default 1.1% of home price annually (national median of effective property tax rates, 2023-2025 Census ACS data). State pages use state-level effective rates from the same source. You can override in Advanced Options.
Homeowners insurance: default $120/month ($1,440/yr) — near the national average for a $350K home (NAIC 2023 data, ~$1,400-1,500). Overridable.
PMI: conventional loans above 80% LTV — tiered: 0.50% (85-80% LTV), 0.75% (90-85%), 1.00% (95-90%), 1.50% (>95%) of loan balance annually, ÷12 monthly. Assumes 700-759 credit band; your actual rate varies by credit score.
FHA MIP: 1.75% upfront (financed) + 0.55% annual (HUD 2026 schedule, 30-year loans >15% LTV under $726,200).
VA funding fee: 2.15% first use with <5% down (va.gov 2026 rates); exempt for disability-rated veterans.
USDA guarantee fee: 1.0% upfront + 0.35% annual (USDA RD 2026).
HOA: included if you add it in Advanced Options — never assumed by default.

Rate Methodology

Rate anchors come from the Freddie Mac Primary Mortgage Market Survey® (PMMS) weekly release. TruePITI is not a lender and does not quote live rates — we display the most recent PMMS benchmark plus a note that your actual rate depends on credit, down payment, loan type, and location. State page benchmarks are PMMS national averages adjusted with state-level spreads; they are estimates, not quotes.

Rounding & Currency Rules

All dollar figures rounded to whole dollars in displayed results (intermediate calculations keep full precision).
Percentages displayed to one decimal (rates to three, e.g. 6.625%).
Annual totals = monthly × 12; lifetime totals summed from the month-by-month schedule (not multiplied approximations).
Total interest is the sum of every month's interest charge — verified against the amortization identity (total = payment × n − principal).

Data Update Rules

Rate anchors: updated when the PMMS weekly release changes materially.
Loan limits (conforming $832,750, FHA floor $541,287 / ceiling $1,249,125): updated annually when FHFA/HUD announce (typically November-December).
State tax/insurance/price data: annual review against Census, NAIC, and state sources.
Every page shows "Last updated" via the build date — we never claim an update that did not happen.
Errors found are logged on the corrections page.

Limitations

All results are estimates for educational purposes — not quotes, offers, or financial advice.
Your lender's underwriting, escrow calculation, and closing fee schedule will differ.
PMI tiers assume a 700-759 credit band; sub-700 borrowers pay more, 760+ often less.
Property tax and insurance defaults are national medians — always override with your local figures.
See Sources for every data provider used on the site.