An independent quarterly tax calculator.

Who runs this

quarterlytaxplan.com is published by Red Goggles LLC, an independent operator of free web calculators and reference tools. We are not the IRS, a state tax agency, a tax-preparation company, or a tax-software vendor, and we are not affiliated with or endorsed by any of them. We don't sell tax software, we don't collect leads, and we don't take your information — the calculator runs on your device and nothing you type is sent to us.

Why this site exists

Most people who owe quarterly estimated taxes don't think of themselves as "quarterly filers" — they're gig workers, freelancers, consultants, S-Corp owners, retirees with conversion income, or people who left a W-2 job partway through the year. The IRS expects tax to be paid as income is earned, and the underpayment penalty catches people who wait until April. The rules that let you avoid it — the safe harbor and the four staggered due dates — are well defined but unfamiliar. The reason this tool exists is to answer one question quickly and correctly: how much should I send this quarter?

How it's calculated

The estimate is built from published federal figures, applied in the open:

• Safe harbor — the lower of two amounts. You only need to pay the smaller of 90% of the current year's projected tax, or 100% of the prior year's tax (110% if your prior-year AGI was over $150,000, or $75,000 if married filing separately). The threshold is prior-year AGI, not current. The tool computes both and uses whichever is lower, per IRS Publication 505 and Form 1040-ES.
• Self-employment tax on top of income tax. Net self-employment earnings carry a 12.4% Social Security component up to the annual Social Security wage base (announced each October by the SSA) plus 2.9% Medicare on all earnings, with an additional 0.9% Medicare above the filing-status thresholds. SE tax is separate from income tax but paid in the same quarterly voucher.
• The four due dates. April 15, June 15, September 15, and January 15 of the following year — not calendar-quarter ends. When a date falls on a weekend or federal holiday it shifts to the next business day, which the tool computes dynamically.
• State schedules. Most states with an income tax mirror the federal schedule; some (such as California) use a non-uniform split; nine states have no income tax and no quarterly requirement. State figures use each state's published brackets; verify against your state's department of revenue.
• Underpayment interest. The IRS underpayment interest rate is set under Internal Revenue Code Section 6621 and changes every quarter, so any penalty figure is an estimate at the rate shown and should be checked against the current published rate.

How we stay accurate and current

We model current enacted federal law and cite primary sources — the IRS (Publication 505, Form 1040-ES, Form 2210), the SSA for the wage base, and each state's department of revenue. Several inputs change on a schedule: the Section 6621 interest rate quarterly, the Social Security wage base annually in October, and the federal brackets and standard deduction annually. We refresh those figures as the official releases come out and date every page. Where a figure is an approximation (a rough state estimate, or a rate that has since changed), we say so rather than imply precision we don't have.

How the site is funded

quarterlytaxplan.com is free and supported by display advertising. Advertising never mixes with your inputs — see our privacy page for exactly what is and isn't collected.

Questions or corrections? We take accuracy seriously on a topic this consequential — reach us on the contact page.