Payable on Arrival: Do I need to make estimated tax payments?
Income tax is due four times a year, not once in April. A salary satisfies all four automatically; everything else is yours to send.
If a salary is all you've ever earned, you've probably never once paid your taxes on purpose. Your employer did it for you, every two weeks, in roughly the right amount, on a schedule you never needed to know about.
Payroll reads your W-4, guesses your bracket, sends a slice of every paycheck to the Treasury, and by December it's satisfied four separate deadlines you never had to see.
Which means April is when you reconcile what payroll already paid with what you actually owed.
But outside of W-2 employment, the picture gets more complicated. A savings account pays interest, a brokerage throws off dividends and gives you a few realized gains. RSUs start vesting. You exercise options, a consulting invoice clears.
None of it runs through payroll the way a paycheck does, and some of it isn't withheld at all. Which is when the schedule underneath becomes your problem.
The federal income tax has four due dates: April 15, June 15, September 15, and January 15. Miss one and interest starts running on that installment the next morning, even if you pay the entire bill on time the following spring. The IRS calls it an underpayment penalty; it's really just interest.
Withholding and estimated payments are not two different obligations. They are the same one, arriving by two different routes — automatically, out of a paycheck, or manually, from you. Whatever the first route doesn't cover, the second one has to.
Why do I owe a penalty if I paid by April 15?
Whether you knew it or not, the tax on anything your employer didn't withhold for you was due before April 15.
Each installment stands on its own, and the interest on a missed one runs from its own deadline to the day you finally pay, so a shortfall in April is still accruing eleven months later when you sit down to do your return.
The quarters are also not quite quarters:
- 3 monthsFirst payment
- due April 15
- covers January to March · 3 months
- 2 monthsSecond payment
- due June 15
- covers April and May · 2 months
- 3 monthsThird payment
- due September 15
- covers June to August · 3 months
- 4 monthsFourth payment
- due January 15
- covers September to December · 4 months
The second window is two months long, the fourth is four. The first payment of the year is due before you know almost anything about the year, and the last arrives two weeks after it ends.
For a salary, withholding satisfies all four without you touching it. For anything that doesn't run through payroll, meeting them is on you.
How do I avoid the penalty?
There is a threshold, and it's more forgiving than it sounds. Send in at least this much across the four deadlines and the penalty is zero, no matter how big the real bill turns out to be. The tax code calls that threshold the safe harbor.
Two numbers qualify, and you only have to reach the smaller one:
- 90% of what you owe this year. Exact, and it requires knowing in April what your year will look like in December.
- 100% of what you owed last year. A number already printed on a form you have. If last year's adjusted gross income was over $150,000, it becomes 110%.
Everything above that minimum is still due on April 15, in full. It just arrives with no interest attached.
"Last year's tax" means the whole tax you owed for the year, not the check you wrote in April. The check was only the part your withholding hadn't already covered, so it is much smaller. Aim at that by mistake and you underpay all year.
There is also a floor underneath all of this. If the balance left after withholding comes to less than $1,000, there is no penalty at all — which is why most people with a salary and a small brokerage account never think about any of this.
What does it cost if I come up short?
The interest runs about 7% a year, compounded daily, separately on each installment, from that installment's own deadline. It is not deductible, and you pay it on the amount you were short, for exactly the days you were short it.
It is also the one penalty you cannot argue with. There is no reasonable cause relief for it in any ordinary situation, no first-time abatement, no phone call that makes it go away. It is arithmetic on a form, and a good preparer will simply add it to your return.
That cuts both ways. Because it is only interest, it is survivable — on a large bill, a missed installment costs less than people fear. What it is not is optional.
How much do I send?
It comes down to four numbers: what you earned and what you owed last year, what you expect to owe this year, and what your paychecks are already covering.
Your safe harbor this year
$40,370
is 110% of last year’s tax, the smaller of the two numbers that qualify. Pay it in and the rest of the bill waits until April, free.
What to send, and what skipping costs
Per quarter, four times
$2,593
On April 15, June 15, September 15, and January 15.
Or skip all four, and April costs
$30,496
The whole bill in one check, carrying $496 of interest you never had to pay.
If your withholding already clears the bar, you are done, and the rest of the bill waits until April with no interest attached. The most common reason it doesn't clear is an RSU vest: payroll withholds those at a flat 22% regardless of your bracket, and that trap gets its own letter, arriving next week.
What's your next move?
Payroll has been meeting these four deadlines on your behalf since your first paycheck. That is the whole reason you have never had to know they exist.
Nothing about the deadlines changes when your money starts arriving from somewhere else. Only who is responsible for them does.
The tax was never due in April. April is when they check.