The ChatGPT prompt that estimates your quarterly tax in 2 minutes

Quarterly estimated taxes are the worst part of being self-employed.

Not the worst because they're hard — they're not, mathematically. The worst because they sneak up on you four times a year, demand a precision calculation across income types and deductions you barely tracked, and the IRS punishes you for getting it wrong. Most freelancers either pay too much (interest-free loan to the government) or pay too little (penalties).

I built one prompt that handles 95% of the calculation work. You paste your income and expenses, hit run, and get a structured estimate with the exact amount to wire to the IRS and your state. It takes two minutes. Here it is.

What this prompt actually does

You give Claude or ChatGPT three things: your year-to-date income, your year-to-date business expenses, and your state. The prompt then walks through the standard freelance tax math — self-employment tax (15.3% of net earnings), federal income tax (based on your projected annual income), and an estimate for state tax. It outputs a specific dollar amount for your next quarterly payment.

The reason it works is structure. AI is unreliable when asked open-ended questions about taxes. But when given a precise calculation framework and the exact numbers to plug in, it performs consistently. This prompt is essentially a guided calculator with a friendly interface.

The prompt

Why the structured format matters

If you ask ChatGPT "how much should I pay in quarterly taxes" without structure, you'll get a vague answer about consulting a tax professional. The prompt above works because it removes ambiguity. You're not asking for tax advice — you're asking the AI to perform a defined calculation on numbers you've already gathered.

The "show your work" instruction is the most important line in the prompt. It forces the AI to walk through each step, which means you can spot if it skipped or miscalculated anything. If a number looks wrong, you can immediately see where the error happened.

The numbers you actually need to gather

Before running the prompt, spend ten minutes collecting:

1. Year-to-date income: Total of all 1099 payments, direct client payments, and any other freelance revenue. Check your business bank account or Stripe dashboard.
2. Year-to-date expenses: Software subscriptions, professional services, home office portion of rent (if applicable), equipment, mileage, marketing costs, business meals (50% deductible).
3. Filing status: Single, married filing jointly, head of household, etc.
4. State of residence: Affects state income tax calculation.
5. Anything already paid: If this isn't your first quarterly payment of the year, sum what you've already paid in federal and state estimated taxes.

You can run this prompt with rough numbers if exact figures aren't handy — even a ballpark output is better than panic-paying on April 14th.

When to run this prompt

Quarterly estimated tax due dates (US):

• Q1: April 15 (for January–March income)
• Q2: June 15 (for April–May income)
• Q3: September 15 (for June–August income)
• Q4: January 15 of the following year (for September–December income)

Run the prompt two weeks before each deadline. That gives you time to verify the numbers with your tax software or CPA, and time to actually wire the payment through the EFTPS system before the cutoff.

The safety-net version

If you don't want to deal with this prompt every quarter, here's the freelancer's safe rule of thumb: set aside 30% of every payment you receive into a separate savings account labeled "Taxes." When quarterly deadlines hit, pay from that account. You'll over-save slightly in most cases, but you'll never be caught short and you'll never panic-borrow to make a tax payment.

The prompt above gives you more precision. The 30% rule gives you peace of mind. Use both — the prompt for accuracy, the rule for protection.