If you earn money without an employer withholding taxes for you, the IRS expects a payment four times a year, not once in April.
The next deadline is September 15, and it catches a surprising number of freelancers, gig workers, and small business owners off guard.
Here is the part that trips people up: the penalty for skipping these payments is not a flat fee you can shrug off.
The IRS charges interest that compounds daily on the amount you should have paid, and the rate has been hovering around 7% to 8% in recent quarters.
On a $10,000 shortfall, that can quietly add several hundred dollars to your bill.
The rule of thumb is that you owe quarterly payments if you expect to owe at least $1,000 in taxes for the year.
That threshold is low, which means side hustlers with a modest Etsy shop or a few DoorDash weekends can land in the crosshairs without realizing it.
There are two safe ways to calculate what you owe.
You can pay 90% of this year's total tax bill across the four quarters, or you can pay 100% of last year's bill, whichever is smaller.
If your adjusted gross income topped $150,000, that second option jumps to 110% of last year's figure.
Meeting either target shields you from the underpayment penalty, even if you end up owing more in April.
Each payment covers income earned during a specific window, so a huge December freelance check does not have to be paid until the January deadline.
But if you had a windfall back in March and skipped that quarter, you cannot fully fix it by overpaying later—the IRS tracks the timing.
A simple way to stay ahead is to set aside 25% to 30% of every payment you receive into a separate savings account.
When the deadline arrives, the money is already there and you are not scrambling.
Many online banks let you label sub-accounts, which makes this nearly automatic.
If you also hold a regular job with a W-2, you have another lever.
You can ask your employer to withhold extra from each paycheck by filing a new W-4.
Because withholding is treated as paid evenly throughout the year, bumping it up can erase an underpayment penalty from freelance income without you writing a single quarterly check.
The IRS takes payments through IRS Direct Pay, its online account system, and the Electronic Federal Tax Payment System.
Credit card payments are accepted through third-party processors, but expect a convenience fee near 2%, which usually wipes out any rewards you were chasing.
One more thing worth checking: if you live in a state with income tax, most states run their own quarterly system with deadlines that mostly mirror the federal dates.
Missing the state payment can mean a second penalty stacked on top of the federal one.
My take: quarterly taxes feel like a chore invented to punish people for working for themselves, but the penalty math makes ignoring them genuinely expensive.
Setting aside a slice of each payment takes ten minutes to arrange and saves real money.
Final Thoughts
Treat the September date like any other bill, and April stops being a nasty surprise.