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Methodology & Editorial Standards

Last updated: June 9, 2026

We hold our calculators to a simple standard: if a number appears on this site, it should trace back to an official formula, law, or government publication - not a rule of thumb.

A deterministic rules engine

Every calculation runs through a deterministic rules engine. Inputs, thresholds, rates, and eligibility conditions are defined as data and evaluated the same way every time, so a given set of inputs always produces the same, reproducible result. We use AI only to explain a result in plain language or to translate it - never to decide an amount or whether you qualify.

Official sources we rely on

By region, the primary sources behind our tax, benefit, and property calculators are:

  • United States: Internal Revenue Service (IRS), Social Security Administration, Medicaid.gov, state revenue departments, and county assessors.
  • United Kingdom: GOV.UK, HM Revenue & Customs (HMRC), and local councils.
  • Canada: Canada.ca, the Canada Revenue Agency (CRA), and provincial benefit and tax authorities.

Transparency on every calculator

  • Last verified date - when we last confirmed the figures against the source.
  • Official source links - so you can check the rule yourself.
  • Confidence level - high, medium, or low, reflecting how clearly the rules apply to your inputs.
  • Clear disclaimers - every result states that an estimate is not tax, legal, or financial advice.

Keeping figures current

Tax years change, credits are adjusted for inflation, and thresholds move. When that happens we update the affected calculators and refresh their "last verified" date. Our flagship US Child Tax Credit calculator, for example, reflects the figures in force for the 2025 tax year.

When we can't be exact

Some situations are genuinely complex - multiple dependents with different statuses, foreign income, or rules that vary by county. In those cases we tell you that local review is needed rather than presenting a falsely precise figure. The tools are a fast, well-sourced starting point, not a replacement for the relevant agency or a qualified professional.

Reporting an error

Found a figure that looks wrong? Please tell us at hello@online-calc.com with the calculator, your inputs, and the result you expected. We investigate every credible report and correct confirmed issues promptly.