The fourth payment is the one you can get right on purpose. By now you know your income, your expenses, and what you already paid. This guide turns that into a number you can pay with confidence, plus the year-end moves that lower it.
Find yours. Each one tells you which part of this page to use and the thing most likely to trip you up.
Q4 covers income from September 1 through December 31, 2026. Most states share the January 15 deadline. A few differ, so check yours.
Dec 31, 2026
Last day for moves that count for 2026
Retirement contributions, equipment, and any state payment you want deducted on your 2026 return.
Jan 15, 2027
Q4 federal payment due
Pay online by 11:59 pm Eastern. Most states match this date.
Feb 1, 2027
Skip-the-payment exception, and 1099s arrive
File your full return and pay everything by this date and the IRS waives the January payment. Few can, since 1099-NECs ($2,000 and up this year) land the same day.
Mar 15, 2027
S corp returns due
Form 1120-S. An extension pushes this to September. Also the deadline to elect S corp status for 2027.
Apr 15, 2027
2026 return due, and Q1 2027 payment due
Both on the same day. If Q4 came out high, build that into your Q1 estimate.
Safe harbor is the number to pay. It protects you from penalties and takes five minutes with last year's return. The ballpark tab is for anyone whose income changed a lot this year and wants to know roughly what April holds.
The IRS will not charge an underpayment penalty if your 2026 payments add up to at least 100% of your 2025 total tax, or 110% if your 2025 adjusted gross income was over $150,000 ($75,000 married filing separately). Income going up this year changes nothing here. Hit this number and you are protected, even if you owe more in April.
2025 total tax
Form 1040, line 24
2025 adjusted gross income
Form 1040, line 11. Includes a spouse's income if you file jointly
Safe harbor target
A × 100%, or A × 110% when B is over $150,000
Federal estimated payments made in 2026
Your IRS online account lists them, or add up your receipts
Federal tax withheld from any W-2 job
Yours or a spouse's. Year-to-date on the latest pay stub, projected to Dec 31
Your Q4 safe harbor payment (C minus D minus E)
$0
Federal only. Add your state's Q4 estimate on top.
A therapist's 2025 return shows $14,200 total tax and $96,000 AGI, so her target is $14,200. She paid $3,600 in April and $3,600 in June, then skipped September during a slow stretch. No W-2 withholding. Her Q4 safe harbor payment is $7,000. She can pay it by January 15 and owe no penalty on the year, even though the skipped quarter created a small one for September through whenever she pays.
Two things to know. The IRS counts estimated payments quarter by quarter, so a missed Q3 still generates a small penalty until you catch up. W-2 withholding is treated as paid evenly through the year, which is why raising it in December can erase a shortfall that an estimated payment cannot. And if your practice grew a lot in 2026, safe harbor avoids penalties but leaves a balance for April. That is what the ballpark tab is for.
If 2026 looks very different from 2025, safe harbor keeps you penalty-free but tells you nothing about April. This gives you a range for the real bill so January's decision (pay it now or hold it) is an informed one. An actual number needs your categorized books, the federal brackets, the QBI deduction, and your state, which is what a quarterly estimate from Heard runs.
2026 net profit, best guess
Everything paid to you this year minus practice expenses. Round it. Estimate Sept through Dec if your books lag
How your practice is taxed
S corp owners pay Social Security and Medicare through payroll, so the range drops
Already paid in 2026
Estimated payments plus any W-2 withholding
Likely 2026 federal total, before what you paid
$0
Likely still owed after what you paid
$0
Federal only, built from a 15.3% self-employment tax (sole props) and a 12 to 18% income tax band that fits most solo therapists. A spouse's salary, a second state, or a big deduction moves you outside it. Pay at least the safe harbor number either way; this range tells you how much more to set aside.
Q4 is the only payment you can still shrink before you make it. Every item here has to happen in 2026 to count for 2026.
Federal payments go through your IRS Individual Online Account at irs.gov, which also lists every estimated payment you made this year. Choose tax year 2026 and the reason "estimated tax." Direct Pay from a bank account is free. State payments go through your state's department of revenue site. Pay both from the business bank account and save both confirmation pages somewhere you will find them in March. The IRS does not mail a receipt.
If you cannot pay the full amount, pay what you can by January 15. The penalty works like interest on the shortfall, currently in the 7 to 8% range annualized, and stops accruing on whatever you pay.
Forgetting a W-2
Withholding from your job or your spouse's counts toward safe harbor. Leave it out and you overpay in January and wait until April to get it back.Using 100% when the rule is 110%
The $150,000 line is based on your 2025 return and includes a spouse's income if you file jointly. Many therapist households cross it without noticing.Treating the state as an afterthought
State penalties are separate, and some states have lower thresholds than the IRS. Practice in two states and each wants its share.Planning to sort it out in April
The penalty clock runs from January 15. April costs three months of interest on the full amount plus whatever Q3 shortfall already exists.Already underpaid earlier in the year? Pay the full catch-up amount by January 15, keep the receipts, and let your preparer file Form 2210 if a small penalty applies. If your income was uneven, the annualized income method on Form 2210 can shrink or erase the penalty by matching each quarter's required payment to what you earned then. Ask about it if your fall was much busier than your spring.
The math above is already done for you. Your estimate is built from what is in Heard, and December is when most of the things it cannot see yet happen. Run this list before you pay and your Q4 number reflects the year you had.
Missed the checklist deadline this quarter? The Safe Harbor Calculator in your account gives you the same number as the safe harbor tab above, so you can still pay on time.
Heard keeps your books current, calculates your federal and state estimate from how your practice is doing this year, reminds you a week before each deadline, holds your receipts, and carries every payment into your return at filing time. The number you pay in January is the number that shows up on your return in April.
See how quarterly estimates workHeard's Q4 quarterly taxes webinar is November 19. We run the calculation live, take questions on the edge cases (uneven income, multi-state, S corps, spouses), and show what the estimate looks like inside Heard.
Register for November 19General tax information for therapists in private practice, current as of November 2026. It does not account for your full situation. For advice specific to your practice, work with a licensed tax professional.