Editorial policy

What we publish

Keystone publishes 12 real estate and mortgage calculators for the US market, each with a guide that explains the method, and state editions that start from each state's own figures. Everything is free to use, with no sign-up.

How the math is checked

• Formulas are published. Every calculator lists the formulas it uses and the assumptions behind them, next to the tool.
• Worked examples come from the same code. Each guide's example is computed by the same functions as the live calculator, so the text can't drift from the tool. You can check any of them by hand.
• Assumptions are labeled. Where a figure is an estimate rather than sourced data, such as a typical insurance premium, the page says so.

Where the data comes from

State editions and the state rankings use these sources, each cited with its date on the pages that use it:

• Typical home value: Zillow Home Value Index (all homes, mid tier, seasonally adjusted), September 2026.
• Median household income: U.S. Census Bureau, American Community Survey 1-year estimates, table B19013, 2024.
• Median gross rent: U.S. Census Bureau, American Community Survey 1-year estimates, table B25064, 2024.
• Effective property tax rate: Median real estate taxes paid (B25103) ÷ median home value (B25077), Census ACS 1-year, the Tax Foundation's method, 2024.
• Homeowners insurance: Keystone estimate of a typical annual premium. Replace it with a quote for the address, 2026.

We don't invent figures. When a source isn't available, the value is labeled as an estimate.

Reviews and updates

Every calculator page shows the month it was last reviewed. When a loan program rule, limit, or data source changes, we update the affected calculators, their worked examples, and that date.

Corrections

If you find an error, email help@keystonecalculators.com or use the contact page. We check every report, fix confirmed errors, and update the page's review date.

Advertising and independence

• The site is paid for by display advertising from Google AdSense.
• Advertisers don't see or influence our formulas, data, or text. We have no lender partnerships, no paid placements, and no lead forms.
• Ads are labeled “Advertisement” and kept apart from the calculators, so they can't be mistaken for part of a tool.

Not advice

Our calculators produce educational estimates, not financial, tax, legal, or lending advice. A lender's quote, an appraisal, and a tax professional decide the real numbers. See the disclaimer.