Tax Checkup & S-Corp Calculator by M.F. Witherspoon

Free tax checkup & tracker for business owners: estimate your taxes, test an S-Corp, and never miss a quarterly payment.

Am I overpaying in taxes? Find out in two minutes. Built by the CPAs at M.F. Witherspoon & Co., this free toolkit gives business owners, freelancers and self-employed professionals a clear picture of their taxes. Your numbers never leave your browser. TAX CHECKUP Enter your revenue, expenses, filing status and state to see: • Your estimated total tax: federal income tax, self-employment tax and state tax • How much you've paid so far, and whether you're facing a shortfall • Your effective rate and what your next $1,000 of profit will cost • Personalized savings opportunities, each with an estimated dollar value. Examples include an S-Corp election, Solo 401(k) contributions, the 20% QBI deduction, hiring your children, the state PTE tax election, equipment and vehicle write-offs, and home office deductions S-CORP CALCULATOR Is an S-Corp worth it for you? • Side-by-side comparison: self-employment tax vs. S-Corp payroll tax • Includes the effect on your QBI deduction, state taxes and added payroll costs • A salary slider and sensitivity table show how "reasonable compensation" changes your savings • A break-even profit estimate MY YEAR TRACKER Keep an eye on your taxes all year, not just in April. • Your numbers are saved, so they're waiting every time you open the extension • Enter "year to date" figures and get a full-year projection • One-tap buttons to log new income, expenses and tax payments, with undo • "Since your last update" changes and a chart of your estimated tax vs. payments • Quarter-by-quarter payment tracker, plus a reminder badge on the icon before each deadline • Carry your settings into the new year in one click • Download a backup anytime QUARTERLY TAX PLANNER Avoid IRS underpayment penalties. • Calculates your safe-harbor amount (90% of this year's tax, or 100%/110% of last year's) • Exact due dates, adjusted for weekends and holidays • Shows if you're behind and how much to catch up • Add every deadline to your calendar in one click ALWAYS UP TO DATE • Uses the latest IRS brackets, standard deductions, Social Security wage base and retirement limits (currently 2025 and 2026 under the One Big Beautiful Bill Act) • All 50 states plus DC • When the IRS releases a new year, official federal figures arrive automatically from the open-source PSL Tax-Calculator project. They're verified against built-in IRS data first, and future years are projected until then PRIVATE BY DESIGN • All calculations run locally on your computer • No account, no sign-up, no tracking, no ads • Your numbers are saved only on your computer, never uploaded or synced • No warnings at install. It can't see the websites you visit WANT A CPA TO CHECK YOUR NUMBERS? Book a free consultation with M.F. Witherspoon & Co. right from the extension. We serve clients in Florida and nationwide, in English and Spanish. mfwitherspoon.cpa · 786-568-7255 Estimates are for educational purposes only and are not tax advice.