Safe-harbor target
The tool uses a simplified annual target based on prior-year total tax, with a 110% toggle for higher-income cases.
Public help / FAQ
How QuarterlyTaxCheck works
QuarterlyTaxCheck helps US freelancers, 1099 contractors, and solo business owners estimate safe-harbor coverage, next payment gap, and underpayment risk using a simplified public model.
What you need before you start
- Your prior-year total federal tax
- Whether your prior-year AGI was above the higher-income safe-harbor threshold
- Estimated federal payments already made this year
- Expected full-year federal withholding
- Year-to-date and expected full-year net self-employment income
Coverage
The tool compares your annual target against estimated payments already made and expected withholding.
Catch-up baseline
You see the remaining gap, remaining installments, the next due date, and a suggested next payment baseline.
FAQ
What is prior-year total tax?
Use the total federal tax amount from your prior-year return. This is the baseline the tool uses for a simplified safe-harbor check.
What is safe harbor?
In this tool, safe harbor means a simplified annual payment target based on prior-year total tax. Many taxpayers use this concept to reduce underpayment-penalty risk.
Does withholding count?
Yes. The tool includes expected federal withholding because it can materially change how much estimated tax you still need to send.
What if my income is uneven?
The result becomes less reliable when income varies heavily during the year. Annualized-income methods or professional review may be more appropriate.
Does this calculate my exact tax bill?
No. It gives a planning baseline, not a full tax calculation or filed return.
Does this include state estimated taxes?
No. QuarterlyTaxCheck is focused on federal planning only.
Important limitations
- Not tax advice, legal advice, or accounting advice
- Not a filing tool or bookkeeping platform
- Does not fully model credits, deductions, multiple income streams, or state taxes
- Does not guarantee penalty avoidance
If your case is complex, use this tool as a starting point and review the result with a tax professional.