Quarterly Estimated Taxes for Locum Tenens Clinicians

Yes, if you expect to owe $1,000 or more in tax for 2026 after subtracting your withholding and refundable credits. Estimated taxes are the pay-as-you-go system the IRS uses for income that has no withholding — and 1099 locum pay has none. When you were a W-2 employee, your hospital withheld income tax, Social Security, and Medicare from every paycheck. As an independent contractor, nothing is withheld, so the IRS expects you to send the equivalent in four installments across the year.

This catches most first-year locums off guard for one reason: estimated tax is not just income tax. The IRS is explicit that estimated tax 'is used to pay not only income tax, but other taxes such as self-employment tax and the alternative minimum tax.' That self-employment (SE) tax — the 15.3% that covers Social Security and Medicare — used to be split with your employer and withheld automatically. On 1099 income you owe all of it, and there is no withholding to cover it. If you set your estimates by income tax alone, you will be roughly 14% short before you start.

If you carry a mix of W-2 and 1099 work, the W-2 withholding counts toward your total tax, which can reduce or eliminate the estimates you owe — but only if that withholding is large enough to clear a safe harbor.

The 2026 federal estimated-tax cycle has four payments: April 15, 2026; June 15, 2026; September 15, 2026; and January 15, 2027. Note the quarters are not equal calendar quarters — Q2 covers only two months and Q4 covers four. All four 2026 dates fall on a weekday (April 15 is a Wednesday, June 15 a Monday, September 15 a Tuesday, January 15, 2027 a Friday), so no weekend or holiday shift applies this cycle.

There is a Q4 shortcut worth knowing: if you file your full 2026 return and pay the entire balance due by January 31, 2027 (which becomes February 1, 2027 because January 31 is a Sunday), you can skip the January 15 payment entirely. In practice this is hard for self-preparers to pull off, because it means finalizing your whole return in the first weeks of January.

Each federal date is also when many state estimates are due — but not all. State schedules vary, and some states front-load. Track every applicable state's calendar separately (see the multi-state section below).

Pay the smaller of two targets and you are protected from an underpayment penalty: (1) 90% of the tax shown on your 2026 return, or (2) 100% of the tax shown on your 2025 return — but that prior-year figure rises to 110% if your 2025 adjusted gross income (AGI) was over $150,000 ($75,000 if married filing separately). Divide your chosen target by four and pay that each quarter.

For this audience, the 110% number is the one to internalize. Most full-time locum physicians, CRNAs, and AAs clear $150,000 AGI, so their prior-year safe harbor is 110%, not 100%. Guides that quote a flat '100% of last year' are simply wrong for most readers here — relying on 100% when your AGI was over $150,000 leaves you 10% short and exposed to a penalty.

The prior-year safe harbor is especially useful in your first 1099 year: if 2025 was a lower-tax W-2 year, 110% of that smaller number may be modest, lowering your required quarterly payments. You will still owe the real balance at filing — the safe harbor only protects you from the underpayment penalty, not from the tax itself.

One planning note: don't shrink your estimate by assuming a 20% QBI (§199A) deduction. Physicians, CRNAs, and AAs are a specified service trade or business (SSTB) in the field of health. For 2026 the SSTB deduction fully phases out above $276,750 single / $553,500 MFJ (Rev. Proc. 2025-32) — so most full-time locums get a $0 QBI deduction and should plan their estimates accordingly.

Self-employment tax is 15.3% — 12.4% for Social Security plus 2.9% for Medicare — and it is the single largest line most new locums forget to put in their estimates. You calculate it on 92.35% of your net self-employment earnings (this adjusted figure is your 'SE base'). The 12.4% Social Security portion applies only to the first $184,500 of SE base in 2026 (the Social Security wage base); the 2.9% Medicare portion applies to all of it with no cap.

High earners owe an extra 0.9% Additional Medicare Tax on earnings above $200,000 (single) or $250,000 (married filing jointly). You also get to deduct one-half of your SE tax 'above the line,' which reduces your AGI and therefore your income tax — but not your SE tax.

If you mix W-2 and 1099 work, any Social Security wages from your W-2 job fill the $184,500 cap first, which reduces the 12.4% portion you owe on your 1099 SE base. The Medicare 2.9% (and the 0.9% surtax) still apply to everything.

The practical takeaway: SE tax runs roughly 14% effective on net locum income, and unlike your old W-2 paycheck, nobody withholds a cent of it. Build it into every quarterly payment.

There is no flat fine — the underpayment penalty is interest-based. The IRS calculates it on three things: the amount of each quarter's underpayment, the number of days that shortfall went unpaid, and the published quarterly underpayment interest rate. That rate equals the federal short-term rate plus 3 percentage points, compounds daily, and resets every quarter under IRC §6621. For 2026 it is 7% in Q1, 6% in Q2, and 7% again starting July 1 (Q3).

The critical mechanic is that each quarter is tested separately on Form 2210. You cannot fix an underpaid Q1 or Q2 by sending a big check in December — the earlier quarters were still short for the months they went unpaid, and interest accrues on each one. Backloading does not work.

There is one important exception to the per-quarter rule: tax withheld from wages (yours or, if you file jointly, a spouse's W-2) is treated as paid evenly across the whole year, no matter when it was actually withheld. That makes spousal withholding a useful planning lever — bumping up a spouse's W-2 withholding late in the year can retroactively cover earlier quarters in a way that direct estimated payments cannot.

You owe no penalty at all if your balance due is under $1,000, or if you met one of the safe harbors above.

For a new locum, the answer is IRS Direct Pay or an IRS Online Account — not EFTPS. This is a recent change many older guides miss: EFTPS (the Electronic Federal Tax Payment System) stopped accepting new individual enrollments on October 17, 2025, and individuals are transitioning off EFTPS.gov during 2026. EFTPS remains the workhorse for businesses and S-corporations, and individuals already enrolled before the cutoff can keep using it for now, but a doctor going 1099 for the first time should not try to 'set up EFTPS.'

IRS Direct Pay is free, pulls directly from your bank account, requires no enrollment (there's a guest path), and lets you schedule payments up to 365 days in advance — convenient for locking in all four 2026 dates at once. An IRS Online Account does the same and adds a running record of your payments and balance. Form 1040-ES paper vouchers still work if you prefer to mail a check, and debit/credit card payments are available through IRS-approved processors (which charge a fee).

State estimates are paid separately, through each state's own tax portal — the IRS systems only handle federal tax.

No. You make federal estimates and separate state estimates for every state that taxes your locum income, and the rules are not uniform. State estimated-tax schedules and safe-harbor percentages vary widely — some states track the federal four-date calendar, others front-load their installments, and prior-year safe-harbor percentages differ from the federal figures. Verify each state's current schedule and safe harbor directly with that state's tax authority.

Seven states make this simpler on income they tax: Alaska, Florida, Nevada, South Dakota, Texas, Washington, and Wyoming have no personal income tax (New Hampshire taxes only interest and dividends, not earned income), so work sourced to those states generates no state income tax and no state estimates.

When you work nonresident assignments, your resident state generally gives you a credit for income tax you pay to other states — this prevents double taxation, but it does not relieve you from filing in those other states. Nonresident de-minimis filing thresholds (how little you can earn in a state before you must file), plus how each state recognizes a PLLC or S-corp, also vary by state. If you string together assignments across multiple states, map each one's filing threshold, due dates, and safe harbor — and lean on a CPA, because the interactions are genuinely state-specific.