If you receive income with no withholding on it — freelance work, 1099 contract income, side-hustle revenue, rental income, or investment gains — the IRS does not take a cut each paycheck. Instead it expects you to pay estimated tax four times a year, by April 15, June 15, September 15, and January 15 of the following year. Miss the right amount and the IRS adds an underpayment penalty on top of the tax you already owe. This quarterly tax calculator estimates how much you should send each due date, checks whether you pass the safe-harbor test, and projects the penalty if you fall short.
The single most important idea is the safe harbor: if you pay in enough during the year, the IRS will not charge a penalty even if your final bill is larger. You satisfy the safe harbor by paying the lesser of two numbers — 90% of the tax you actually owe this year, or 100% (110% if your prior-year adjusted gross income was over $150,000) of the tax you owed last year. Enter your expected current-year tax, last year's tax, the amounts you have already paid each quarter, and the current IRS interest rate, and every figure updates instantly.
How to Use
- Enter your Expected Total Tax This Year — your best guess of federal income tax plus self-employment tax on your 1099/side income. If you are not sure, run last year's number up or down by how much your business grew.
- Type Last Year's Total Tax from line 24 of your prior Form 1040. This is the anchor for the safe-harbor calculation.
- Set AGI Over $150,000? to yes if your prior-year adjusted gross income exceeded $150,000 (it is $75,000 if you are married filing separately). High earners must hit 110% of last year's tax, not 100%.
- Fill in the four quarterly payment boxes with what you have actually sent — Q1 by April 15, Q2 by June 15, Q3 by September 15, and Q4 by January 15. If a date has not arrived yet, leave the amount you plan to pay.
- Adjust the Underpayment Interest Rate only if the IRS has published a newer quarterly rate; 8% is a reasonable default.
- Read the result card: the Required Per Quarter tells you the even amount you should have paid each voucher to stay penalty-free, and the Estimated Underpayment Penalty shows your exposure.
The engine computes the safe-harbor threshold, compares it against 90% of this year's expected tax, takes the lower of the two as the required annual payment, divides it by four, subtracts what you have already paid, and then applies the annual interest rate to the shortfall.
How the Safe Harbor Works
The IRS publishes estimated-tax rules in Form 1040-ES and Publication 502. Two tests protect you from the underpayment penalty:
- Current-year test: you have paid at least 90% of the tax you actually owe for this year through withholding and timely estimated payments.
- Prior-year safe harbor: you have paid in 100% of your previous year's total tax (110% when your prior-year AGI was over $150,000).
The required annual payment is the smaller of those two numbers. For example, if you earned far more this year than last, the prior-year safe harbor is usually the easier bar to clear — you pay last year's tax in four equal installments and avoid the penalty even though your real bill is higher. If you earned less than last year, the 90% current-year test becomes the lower bar.
Each quarterly voucher is treated as due on its date, and the IRS charges interest on any quarter where your cumulative payments are behind the required line. The penalty is not a flat fee; it accrues daily at the IRS short-term rate plus 3%, compounded quarterly. This calculator uses an approximate half-year average accrual to give you a planning number, not a final IRS bill.
Why Quarterly Payments Matter
W-2 employees have taxes withheld automatically, so the IRS gets paid throughout the year. People who work for themselves have to mimic that process voluntarily. If you wait until April 15 to settle the whole year, you will not only write a large check but also pay interest on the months the money should have been in the Treasury. For a freelancer earning $120,000 who owes $12,000 in tax, skipping the April and June vouchers can add roughly $100–$200 of penalty — annoying, but easily avoided by paying $3,000 each quarter.
Self-employed filers also owe the 15.3% self-employment tax on top of income tax, so "expected total tax" should include both. A common mistake is to estimate only the income-tax piece and then discover at filing that the SE tax pushes them well below the 90% mark.
Examples
Example 1 — Meeting the safe harbor. A freelancer expects $12,000 of total tax this year, owed $10,000 last year, and is not over the $150,000 AGI threshold. The safe harbor is $10,000 (100% of last year), while 90% of this year's tax is $10,800. The required annual payment is the smaller number — $10,000, or $2,500 per quarter. They have paid $3,000 each quarter ($12,000 total), so they owe $0 of underpayment and no penalty.
Example 2 — High earner underpaying. A consultant expects $12,000 this year, owed $10,000 last year, and their AGI is over $150,000, so the safe harbor jumps to 110% — $11,000. Because 90% of this year is only $10,800, the required payment is $10,800, or $2,700 per quarter. If they paid just $2,000 each quarter ($8,000 total), they are $2,800 short. At an 8% annual rate over roughly half a year, the estimated penalty is about $112.
Example 3 — Large bill. A business owner expects $2,000,000 of tax this year and owed $1,500,000 last year. The 110% high-income safe harbor is $1,650,000, versus $1,800,000 at 90% of the current year, so they must pay in $1,650,000 — about $412,500 per quarter. Paying $400,000 each quarter leaves a $50,000 shortfall and an estimated penalty near $2,000.
FAQ
How much should I pay quarterly?
Pay one quarter of the smaller of (a) 90% of your expected current-year tax and (b) 100% of last year's tax — or 110% if your prior-year AGI was over $150,000. Enter those two numbers above and the calculator shows the exact amount per voucher.
What is the quarterly tax safe harbor?
The safe harbor is the amount of tax you must prepay during the year so the IRS does not charge an underpayment penalty. It is the lesser of 90% of the current-year tax or 100%/110% of the prior-year tax, split across the four 1040-ES vouchers.
What are the 2026 quarterly tax due dates?
Vouchers are generally due April 15 (Q1), June 15 (Q2), September 15 (Q3), and January 15 of the following year (Q4). When a due date falls on a weekend or holiday, it moves to the next business day.
How is the underpayment penalty calculated?
The IRS charges the federal short-term interest rate plus 3%, compounded daily on any quarter where your cumulative payments are below the required line. This tool applies that annual rate to your estimated shortfall over an average half-year; the exact IRS figure depends on your actual payment dates.
Do I have to make quarterly payments?
You generally owe estimated tax if you expect to owe at least $1,000 when you file and your withholding and refundable credits will cover less than 90% of your current tax or 100%/110% of last year's tax. W-2 employees can often cover the shortfall by increasing withholding, which counts as paid evenly throughout the year.
What if my income is uneven through the year?
The basic safe harbor assumes equal quarterly payments, but if your income is seasonal you can use the annualized income installment method (Form 2210, Schedule AI) to pay larger vouchers after your busy season instead of before it. The equal-installment result above is the conservative default.
Disclaimer
This quarterly tax calculator is provided for informational purposes only and does not constitute tax, accounting, or legal advice. Estimates rely on the inputs you enter and the simplified safe-harbor and underpayment rules in IRS Form 1040-ES; actual penalties, rates, brackets, and due dates are set by the IRS and change every quarter. Always verify your payment requirements and any penalty exposure with a qualified tax professional before filing.