Quarterly Estimated Taxes for Locums
By Cory Kleinschmidt
Because no tax is withheld from 1099 pay, you send the IRS estimated payments on four set dates a year. Hit a safe harbor (100% of last year’s tax, or 110% if your prior-year AGI topped $150,000) and you avoid the underpayment penalty, even if you still owe a balance at filing.
If you’re a 1099 locum, the IRS expects its money four times a year, not once at filing. Miss the schedule and you owe a penalty on top of the tax. This guide is the payment mechanics; deductions and entity choice live in the 1099 taxes guide.
4
Payment Deadlines a Year
$1,000
Owe-Threshold to Trigger Estimates
110%
High-Income Safe Harbor
$150,000
AGI Trigger for the 110% Rule
Do Locums Have to Pay Quarterly Estimated Taxes?
Yes, if you expect to owe at least $1,000 in tax for the year and don’t have enough withheld elsewhere, which describes nearly every full-time 1099 locum. Estimated payments cover both your income tax and your self-employment tax, filed on Form 1040-ES. Unlike a W-2 employee, a 1099 clinician calculates and remits these payments across the year to stay penalty-free.
Disclosure: The Doctor’s CPA is a Locumpedia partner.
The one common exception: if you also hold a W-2 job (moonlighting, a part-time employed role), the withholding from that paycheck counts toward your total. You can even increase it to cover your locum income instead of writing quarterly checks. Withholding is treated as paid evenly across the year, which is occasionally useful for fixing a missed quarter.
When Are Quarterly Estimated Taxes Due?
For the 2026 tax year, federal estimated payments are due on four dates:
- April 15, 2026
- June 15, 2026
- September 15, 2026
- January 15, 2027
Note the uneven spacing: the second payment lands only two months after the first, which catches people who assume even quarters. If a date falls on a weekend or holiday it moves to the next business day.
States that have an income tax mostly copy the concept but change the numbers. A few use a different installment split. If you work across state lines (and most locums do), each state’s rule needs its own check.
How Much Should a Locum Set Aside Each Quarter?
Start by setting aside a conservative 30% to 35% of net income as you earn it, then size the actual payments off one of two IRS methods. That range isn’t a rule from the tax code. It’s 15.3% self-employment tax, plus your federal income tax bracket, plus any state tax, rounded up for safety. A separate savings account you don’t touch is the single habit that prevents an April cash crisis.
The two methods:
- Prior-year safe harbor (simplest): take last year’s total tax and pay 100% of it across the four quarters, or 110% if your prior-year adjusted gross income was over $150,000 ($75,000 if married filing separately). It’s a known number, so you can’t miscalculate it.
- Current-year method (more accurate): estimate this year’s total tax and pay 90% of it. Better if your income dropped, since paying 110% of a bigger prior year ties up cash you’ll get back as a refund.
Your self-employment tax rides inside these estimates too, so the roughly 15% you owe as your own employer is remitted quarter by quarter rather than in one April lump.
What Is the Safe-Harbor Rule and the 110% High-Income Version?
The safe harbor is a payment target that keeps you from owing an underpayment penalty. Under IRC Section 6654 you generally avoid the penalty if your timely payments reach the smaller of 90% of the current year’s tax or 100% of the prior year’s tax. For higher earners the prior-year figure rises to 110% once your prior-year AGI tops $150,000.
The distinction that trips people up: the safe harbor protects you from the penalty, not from the balance due. If your income jumped this year, you can hit the safe harbor perfectly and still write a large check in April. That’s not a penalty, it’s a cash-flow event. Fast-growing locums should plan for it rather than be surprised by it.
What Happens if You Underpay or Skip a Quarter?
The IRS charges an underpayment penalty, calculated as interest on the shortfall from each quarter’s due date until it’s paid. Each installment is tested on its own, so a missed second quarter doesn’t ruin the third and fourth. Catching up as soon as you notice stops the meter on that one shortfall. Generally, you may owe the penalty if you still owe at least $1,000 after subtracting withholding and refundable credits and haven’t paid enough to meet a safe harbor.
How This Differs for NPs, PAs and CRNAs
The rules are identical for every 1099 clinician. Only the amounts change with income.
The 110% safe-harbor trigger catches earners differently. The higher prior-year requirement kicks in above $150,000 AGI, which sweeps in most locum physicians and many CRNAs. Fewer NPs and PAs are affected; they more often stay on the 100% figure. See the CRNA guide.
Lower-income APPs may not owe the full quarterly load if a spouse’s withholding or a part-time W-2 role already covers the safe harbor. The math is the same; the inputs are smaller. See the nurse practitioner guide and physician assistant guide.
Key Takeaways
- 1099 locums pay estimated tax four times a year on Form 1040-ES: April 15, June 15 and September 15, 2026, then January 15, 2027.
- The estimates cover both income tax and the 15.3% self-employment tax; nothing is withheld for you.
- Avoid the penalty with a safe harbor: 100% of last year’s tax, or 110% if your prior-year AGI topped $150,000.
- The safe harbor stops the penalty, not the balance due. A big income jump still means a check at filing.
- Each quarter is tested on its own, so a lump sum in Q4 doesn’t fix earlier quarters.
Frequently Asked Questions
What are the 2026 estimated tax due dates?
April 15, 2026, June 15, 2026, September 15, 2026 and January 15, 2027.
Is it better to pay 100% or 110% of last year’s tax?
You must use 110% if your prior-year AGI was over $150,000; otherwise 100% is enough. Both are safe harbors that prevent the penalty.
Can I just pay it all at the end of the year?
No. Estimated tax is tested quarter by quarter, so a lump sum in Q4 still leaves earlier quarters underpaid and penalized.
What if my income is way higher this year?
Hit the prior-year safe harbor to avoid the penalty, but set aside extra, because you’ll still owe the difference at filing.
Do I owe estimated tax if I also have a W-2 job?
Maybe not directly. Withholding from a W-2 paycheck counts toward your total and can be increased to cover your locum income, which some clinicians use instead of writing quarterly checks.
This guide explains how the rules work; it isn’t tax advice for your situation. A CPA can size your specific quarterly payments.