Tax diagnostic
Why do I owe Federal taxes?
Pick the cause that fits your situation. Each calculator uses current IRS brackets to estimate your withholding gap and a sample W-4 adjustment. No account needed — everything runs in your browser.
Choose your cause
Multiple W-2 Jobs
Each employer withholds as if it is your only job. See the real gap when you combine them.
Run this calculator1099 / Gig Income
No employer withholds taxes on freelance or gig income. See how much you owe in Federal income tax and self-employment tax.
Run this calculatorSpouse Started Working
When a spouse starts a new job, both employers withhold too little. Your combined income lands in a higher bracket.
Run this calculatorRaise / New Bracket
A raise can push part of your income into a higher bracket. Your employer may not adjust withholding enough.
Run this calculatorRead the guides
Frequently asked
What is a tax diagnostic?
A tax diagnostic is a short set of questions that isolates why your Federal withholding may not match your liability. You pick the cause that fits your situation and the calculator estimates the gap based on current IRS brackets.
What if more than one cause applies to me?
Pick the one that had the biggest change in the past year — a new second job, new 1099 income, a spouse starting work, or a raise. You can return and run a different calculator any time; your numbers are not saved to our servers.
Do I need to create an account?
No. Each diagnostic calculator runs entirely in your browser. Accounts are only required if you purchase a W-4 Withholding Report, which generates per-employer adjustment details.
Is this tax advice?
No. WhyDoIOwe.com is a calculator, not a tax advisor. Results are estimates based on current IRS brackets and the numbers you enter. You are solely responsible for deciding whether to submit any Form W-4. Consult a tax professional for advice tailored to your situation.
What if my situation is not listed?
The four diagnostic calculators cover the most common causes of unexpected Federal tax bills. If none fit, start with the full calculator on the homepage — it walks through the same questions in a single flow.
Not sure which cause fits?
Run the full calculator on the homepage. It walks through the same questions in a single flow and estimates your Federal tax gap in about two minutes.
Start the full calculatorFree. No signup required.
This is an estimate based on current IRS brackets. You are solely responsible for deciding whether to submit any Form W-4. Consult a tax professional for advice tailored to your situation.