Methodology

Primary sources

Every US tax calculation references at minimum one of:

• 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)
• State revenue department withholding schedules
• Statutory law where IRS guidance is missing or ambiguous (Internal Revenue Code, state codes)

We do not cite secondary sources (news articles, other calculator sites) as primary authority.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 every page. Each calculator lists the specific primary sources it is built from and the date it was last checked, so the figures can be verified independently. We are engaging credentialed reviewers per jurisdiction and will name them on the page once they are in place.
3. Pre-publish QA. Each page is checked for: brand-new schema markup validation, Lighthouse 90+ on Performance / SEO / Accessibility, mobile rendering, working calculator under edge inputs (0, very large, negative).
4. Search Console gate. New programmatic pages are not scaled until pilot batches reach 80%+ indexing within 4 weeks and at least one is generating organic clicks.

Update cadence

• Federal calculators are re-reviewed annually when the IRS publishes new inflation adjustments (typically October).
• State calculators are re-reviewed annually after the state DOR publishes new withholding schedules.
• Mid-year legislative changes (TCJA-style updates, ARPA-style stimulus) trigger ad-hoc reviews within 30 days of enactment.
• The "Last updated" date on every page is the most recent verification date, not the publish date.

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.
• State calculators reflect the published withholding schedule, not the precise dollar-for-dollar return liability (some states have complex deduction phase-outs that we approximate).

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.