If you made money on the side this year — driving for a rideshare app, selling crafts online, or picking up freelance writing gigs — the IRS expects a payment soon, and it may be larger than you think.
The third-quarter estimated tax deadline lands on September 15.
Anyone who earns income that isn't automatically taxed by an employer typically needs to send money to the IRS four times a year: April, June, September, and January.
Miss one, and the penalties start stacking up quietly in the background.
Here's the part that catches people off guard.
The penalty rate for underpayment currently sits near 7% annually, and it's calculated daily.
That means a freelancer who owes $6,000 and skips a quarterly payment could rack up real money in interest — all before their accountant even looks at the return.
The confusion usually comes down to who counts as "self-employed." A full-time employee with a weekend Etsy shop, a retiree doing consulting calls, a teacher tutoring after school — all of them may owe estimated taxes on that extra income.
The IRS doesn't care whether it's your main job or your side hustle.
One common mistake is assuming you're safe because taxes were withheld from your regular paycheck.
If your side income pushed you into a higher bracket, or if it was substantial, the withholding usually isn't enough to cover the gap.
So what should you actually do before the deadline?
Take your net self-employment income so far, multiply by about 15.3% for self-employment tax, then add your regular income tax rate on top.
If that math feels overwhelming, the IRS Direct Pay tool and most tax software can walk you through it in minutes.
Second, pay something — even if it's not perfect.
Underpayment penalties are based on how much you should have paid, but partial payments reduce the damage.
Sending $500 when you owe $1,200 is far better than sending nothing.
Third, look at your options if cash is tight.
The IRS offers installment plans, and a payment plan usually costs less than the penalty you'd rack up by ignoring the bill.
You can set one up online without calling anyone.
Finally, adjust your withholding for next year now.
Ask your employer for a new W-4, or bump up your quarterly estimates.
Fixing it in advance beats scrambling every three months.
The September deadline is easy to forget because it doesn't come with a W-2 or a 1099 in the mail.
It just arrives, and the clock starts ticking on interest. **Our take:** The estimated tax system punishes people who are already juggling irregular income, and that's genuinely unfair.
But the penalty math doesn't care about fairness — it only cares whether you paid.
Final Thoughts
Set a calendar reminder, send what you can, and treat the quarterly payment like any other bill.