If you made money on the side this year, the tax bill you're imagining is probably too small.
The IRS doesn't wait until April to collect from people who work for themselves.
It wants a slice every few months, and the next installment lands September 15.
Miss that date and the penalty isn't a slap on the wrist.
The agency charges interest on what you should have paid, compounding daily, and the rate has been hovering around 7% to 8% — the highest it's been in years.
Most people who owe this money don't realize it until their accountant tells them.
The rule is simple: if you expect to owe at least $1,000 when you file, you're supposed to pay as you go.
That covers freelancers, gig drivers, consultants, and anyone with a side hustle that doesn't withhold taxes.
The tricky part is figuring out how much to send.
The safe harbor rules let you dodge penalties if you pay at least 90% of this year's tax or 100% of last year's — 110% if your income topped $150,000.
Paying last year's number is often the easier math when your earnings are unpredictable.
Self-employment tax runs 15.3% on top of regular income tax, covering Medicare and Social Security.
A freelancer who nets $60,000 can owe more than $9,000 just for that piece.
Most states with income taxes run their own quarterly system, often on different dates.
California, for instance, doesn't always line up with the federal calendar, which is how people end up with two penalties instead of one.
The good news is that adjusting is easy if you catch it now.
You can pay through IRS Direct Pay, set up an account at EFTPS, or just mail a check with a voucher.
If you've already underpaid, you can increase your next installment to close the gap.
If you had a job with withholding for part of the year, you can also ask your employer to take more out of each paycheck using a new W-4.
That's a quiet way to catch up without writing a big check.
One more thing worth knowing: the penalty is calculated per quarter, not per year.
Paying everything in January doesn't erase the charges from earlier missed deadlines.
If you're not sure where you land, the IRS has a worksheet in Form 1040-ES, and most tax software will estimate it for you in a few minutes.
A quick run-through beats a letter from the agency in the spring. **The bottom line:** If you're earning money without an employer withholding for you, the calendar is not your friend.
Final Thoughts
Mark September 15 and January 15 now, and pay something rather than nothing — partial payments still cut the penalty, and the IRS applies them where they help most.