Expertise & Methodology
How Amortio mortgage calculators work — data sources, calculation methods, editorial standards, and update cadence.
Why this page exists
A home is the largest financial commitment most people make. When a calculator influences a 30-year decision, you deserve to know exactly where the numbers come from and how they were computed. This page documents Amortio's data sources, methodology, editorial process, and update cadence so you can decide for yourself whether to trust an output.
Primary data sources
Amortio is built on government and primary-source data.
- Freddie Mac Primary Mortgage Market Survey (PMMS)
National 30-year fixed and 15-year fixed mortgage rates. Updated weekly Thursdays. Used as base rate input on /mortgage-calculator/ and /mortgage-rates/.
- FHFA House Price Index (HPI)
Quarterly home price appreciation data by state and metro area. Powers /home-value/[city]/ trend analysis.
- Census Bureau ACS
Median home value, median household income, and homeownership rate by city. Used for affordability context across 3,300+ city pages.
- CFPB Mortgage Database
Consumer complaint data, originator reports, and average APR vs note rate spreads to flag predatory pricing.
- IRS Publication 936 (Mortgage Interest Deduction)
Federal mortgage interest deduction rules — $750K cap (loans after 2017), grandfathered $1M cap (pre-2018).
- State property tax registries
Effective property tax rates by state for PITI calculations on /affordability-calculator/ and /closing-cost-estimator/.
Calculation methodology
Amortization schedule
Standard fully-amortizing fixed-rate mortgage formula M = P[r(1+r)^n]/[(1+r)^n−1] where M=monthly payment, P=principal, r=monthly rate (APR/12), n=total payments (years×12). Bi-weekly payment option computes 26 half-payments per year for ~13 monthly equivalents.
PMI (Private Mortgage Insurance) drop-off
Per Homeowners Protection Act (HPA), PMI must be removed automatically at 78% LTV based on original amortization schedule, or by borrower request at 80% LTV. We track both in /pmi-calculator/ output.
PITI vs total cost of homeownership
Principal + Interest + Property Tax + Insurance is industry standard. We add HOA fees, mortgage insurance, and reserve maintenance at 1% of home value/year for true total-cost view in /affordability-calculator/.
Refinance break-even
Break-even months = total closing costs / monthly savings. We disclose lender credits and prepaid items separately. Cash-out refi shows tax-deductible interest treatment per IRS §163(h)(3).
Editorial standards
- All calculators run client-side. No PII (income, SSN, address) is transmitted off-device.
- Mortgage rate inputs allow user override — we never quote the user a "personalized rate" from third-party brokers.
- When rate data shown is more than 7 days old, we display the publication date prominently.
- PMI and tax assumptions disclose state-specific variation (TX/NJ/IL high; HI/AL/CO low).
- Articles cite primary sources (Freddie Mac, FHFA, CFPB, IRS) — not aggregator listings.
- Affiliate/referral relationships, if any, are disclosed in footer and at top of relevant articles.
Update cadence
| What | When |
|---|---|
| Freddie Mac PMMS rates | Weekly (Thursday release) |
| FHFA House Price Index | Quarterly (60-day lag) |
| Census ACS city data | Annual (December 5-year estimate release) |
| IRS deduction limits | Annual (November/December IRS Rev. Proc.) |
| State property tax effective rates | Annual + ad-hoc when assessment laws change |
| Article fact-checks | Quarterly review + within 14 days of major rate move (>50bp Fed action) |
Corrections and feedback
If you spot an error, an outdated rate, or a methodology that does not match the cited source, email [email protected]. We respond to factual corrections within 14 days.
Who builds Amortio
See /about/team/ for team backgrounds. Read /about/ for project mission and privacy commitments.