Pay-As-You-Go
The US tax system requires taxes to be paid throughout the year as income is earned, either through employer withholding or quarterly estimated tax payments.
The pay-as-you-go principle means the IRS expects you to pay taxes on income as you earn it, not in one lump sum at the end of the year. For W-2 employees, this is handled automatically through withholding. For self-employed individuals, freelancers, and those with significant non-wage income, it means making quarterly estimated tax payments.
Estimated tax payments are due four times per year: April 15, June 15, September 15, and January 15 of the following year. If you do not pay enough throughout the year, you may face an underpayment penalty, even if you pay the full balance by the filing deadline.
There are safe harbor rules that can protect you from penalties. If you pay at least 100% of your prior year's tax liability (110% if your AGI exceeds $150,000) or 90% of the current year's liability through withholding and estimated payments, you will generally avoid the underpayment penalty.
How it works
Pay-As-You-Go describes the underlying principle of the US tax system: you are expected to pay tax on income as you earn it during the year, not in a single lump sum when you file your return the following spring. For W-2 employees, this happens automatically through paycheck withholding. For the self-employed, freelancers, and anyone with substantial income that is not subject to withholding — investment gains, rental income, or 1099 earnings — the system relies instead on quarterly estimated tax payments made directly to the IRS.
Estimated tax payments are due four times a year: April 15, June 15, September 15, and January 15 of the following year, and each payment is meant to cover roughly a quarter's worth of your expected annual tax. You calculate and remit these using Form 1040-ES, and the amounts you pay show up as a credit against your total liability when you file, the same way withholding does for an employee. Someone with both a job and significant freelance income may need to combine extra W-4 withholding with quarterly payments to stay current.
Missing or underpaying quarterly estimates can trigger an underpayment penalty even if the full balance is paid by the April filing deadline, because the pay-as-you-go rule is about timing, not just the final total. Safe harbor rules offer protection: paying at least 100% of your prior year's total tax liability (110% if your AGI exceeded $150,000) or 90% of the current year's actual liability through withholding and estimated payments together will generally shield you from the penalty, which is why many self-employed taxpayers base their quarterly payments on last year's return rather than trying to forecast the current year exactly.
Example: quarterly payments for a freelancer
A freelancer expects to owe about $12,000 in total federal tax for the year, with no employer withholding at all, and last year's total tax liability was $10,000.
To stay in the safe harbor, they pay 100% of last year's liability — $10,000 — spread evenly across the four quarterly due dates (April 15, June 15, September 15, and January 15), or $2,500 per payment, then settle any remaining balance when they file.
Frequently asked questions
When are quarterly estimated tax payments due?
What happens if I don't make estimated tax payments?
How do I avoid an underpayment penalty as a self-employed person?
Related Terms
Withholding
The amount of federal and state income tax your employer deducts from each paycheck and sends to the IRS on your behalf throughout the year.
Quarterly Estimated Tax
Tax payments made four times a year by self-employed individuals and others with income not subject to withholding. Due dates are April 15, June 15, September 15, and January 15.
Safe Harbor
IRS rules that protect you from underpayment penalties if you pay at least 100% of the prior year's tax (110% if AGI over $150,000) or 90% of the current year's tax.
Penalty
A charge imposed by the IRS for filing late, paying late, or underpaying estimated taxes. Common penalties include failure-to-file (5% per month) and failure-to-pay (0.5% per month).