If you made money this year without an employer withholding it, the IRS expects a check four times a year — and the third one is due September 15.
Miss it, and the penalty doesn't arrive as a scary letter.
It quietly compounds as interest until you file next spring.
The rule trips up freelancers, gig drivers, rideshare workers, and anyone earning from a side hustle.
When you're your own boss, that job falls to you, and the government wants its cut as the money comes in, not all at once in April.
You generally owe estimated payments if you expect to owe at least $1,000 in federal tax for the year, according to the IRS.
That number is easier to hit than people think — a few thousand dollars of freelance or 1099 income can do it.
The IRS charges interest on underpayments, and the rate moves with the market.
Right now it's steep enough that ignoring the deadlines can cost more than the tax itself for some filers.
The safer route is the "safe harbor" trick.
Pay at least 100% of last year's total tax, or 90% of this year's, whichever is smaller, and you dodge the underpayment penalty even if you end up owing more.
Higher earners — generally above $150,000 — need to cover 110% of last year's bill.
There's a shortcut if math isn't your thing.
The IRS Direct Pay tool and your online account let you schedule a payment in minutes.
You can also bump withholding from a regular job by filing a new W-4, which is often the cleanest fix for people with a salary plus a side gig.
One more thing worth checking: if your income swung wildly this year, the "annualized income installment method" can shrink what you owe for a given quarter.
It's more paperwork, but it can keep you from overpaying early.
A 15-minute payment now beats a surprise bill plus interest later.
Set a calendar reminder for the remaining deadlines — September 15 and January 15 — and treat them like any other bill you can't skip.
Final Thoughts
Your future self, staring at a smaller tax bill in April, will thank you.