Methodology

Primary sources

Our verification standard requires a tax calculation to reference at least one relevant primary source, such as:

• IRS Publications and Revenue Procedures (Pub 15-T, Pub 590-A/B, Pub 560, Rev. Proc. 2025-32 and successors)
• Social Security Administration publications (annual COLA / wage base notices)
• National and state revenue department tax or withholding schedules
• Government pension, social-insurance, and central-bank publications
• Statutory law where agency guidance is missing or ambiguous

We do not cite secondary sources (news articles, other calculator sites) as primary authority. Where we need to interpret ambiguous guidance, we say so on the page.

Review process

1. Author drafts. PennyCompass Team writes the calculator and the on-page explainer based on the primary source.
2. Sources and dates on verified pages. A calculator that has completed review lists the primary sources used and its material review date, so the figures can be checked independently. Pages identified with unverified inputs are restricted rather than receiving a false verification claim. We are engaging credentialed reviewers per jurisdiction and will name them on a page only after they have actually reviewed it.
3. Pre-publish QA. The production build must complete without errors. The calculator must render results for its default inputs, and its source links, metadata, canonical URL, and mobile layout are checked before release.

Update cadence

• Federal calculators enter the review queue when the IRS publishes annual inflation adjustments or material new guidance.
• State calculators are enabled only after their withholding inputs are reviewed against current state guidance; unsupported states remain unavailable.
• Calculators outside the United States enter review when the relevant authority publishes annual rates or rule changes.
• Material mid-year legislation triggers a focused review of the affected formulas and explanations.
• The displayed update date records a material content or calculation change. Source links and explicit review status provide the verification evidence.

Known limitations

Our calculators are accurate for the most common cases but are not full tax returns.

• We do not handle every uncommon edge case (estate-and-trust, foreign income exclusions on hybrid US/foreign filers, etc.) unless the calculator explicitly targets that case.
• We assume the user can pick the correct filing status. We do not check IRS rules on who qualifies for Head of Household.
• We do not compute tax credits (EITC, CTC, education credits, premium tax credit, etc.) unless the calculator is explicitly about a credit.
• Enabled state calculators estimate withholding from the reviewed inputs documented on the page, not a precise dollar-for-dollar return liability. States without reviewed current inputs are not calculated.

When in doubt, the IRS Withholding Estimator and your tax preparer are authoritative. Our calculators are educational.

Corrections

If you find an error in any of our calculators or explanations, please email the address listed on our contact page. We treat finance corrections as priority bugs. Confirmed errors are fixed within 5 business days, and we will publish a correction notice on the affected page if the change is material to results.