Estimated Taxes
for Physicians

Calculating your quarterly estimated tax payment involves three major components: federal income tax, self-employment tax, and state income tax. Let's break each one down.

Step 1: Estimate Your Net Self-Employment Income

Start with your expected gross income from all 1099 sources, then subtract your anticipated business deductions. For most locum physicians, this includes:

• Travel expenses (airfare, lodging, meals, rental cars)
• Professional licensing and credentialing fees
• Malpractice insurance (if you pay your own)
• Home office expenses
• Continuing medical education
• Health insurance premiums (self-employed deduction)
• Business phone, internet, and supplies

The result is your net self-employment income—the starting point for both income tax and self-employment tax calculations.

Step 2: Calculate Self-Employment Tax

Self-employment tax consists of Social Security tax (12.4%) and Medicare tax (2.9%), totaling 15.3%. However, you only pay the 12.4% Social Security portion on income up to the Social Security wage base ($184,500 for 2026). The 2.9% Medicare tax applies to all self-employment income, with an additional 0.9% Medicare surtax on earnings above $200,000 ($250,000 for married filing jointly).

The calculation:

1. Multiply net self-employment income by 92.35% (this is the "self-employment tax base")
2. Apply 15.3% on the first $184,500 of the base
3. Apply 2.9% on amounts above $184,500
4. Add 0.9% Additional Medicare Tax if applicable

Step 3: Calculate Federal Income Tax

Your federal income tax is calculated on your taxable income, which is your adjusted gross income (AGI) minus either the standard deduction ($15,000 single / $30,000 married filing jointly for 2025) or itemized deductions. Key adjustments for self-employed physicians:

• Deductible half of SE tax — You can deduct 50% of your self-employment tax from your gross income
• Self-employed health insurance deduction — 100% of premiums for you, spouse, and dependents
• Retirement plan contributions — Solo 401(k) or SEP-IRA contributions reduce taxable income
• Qualified Business Income (QBI) deduction — Potentially up to 23% of qualified business income (subject to phase-outs for physicians)

The IRS offers two "safe harbor" methods that, if followed, guarantee you won't owe an underpayment penalty—even if you still owe taxes when you file your return. Understanding which safe harbor to use is critical for physician tax planning.

Safe Harbor Method 1: Prior-Year Tax Liability

Pay at least 100% of your prior year's total tax liability through estimated payments and withholding during the current year. If your prior-year AGI exceeded $150,000 ($75,000 for married filing separately), the threshold increases to 110%.

Since virtually every practicing physician has an AGI above $150,000, the 110% rule is the one that matters for you.

Safe Harbor Method 2: Current-Year Tax Liability

Pay at least 90% of your current year's actual tax liability through estimated payments and withholding. This method requires accurately estimating your current-year income and deductions—which can be challenging for locum physicians whose income varies month to month.

Which Safe Harbor Should You Use?

For most physicians, we recommend the following decision framework:

• Your income is growing year over year → Use the 110% prior-year method. It's simple (you know last year's tax), and even though you'll likely owe some additional tax at filing, you won't owe penalties.
• Your income is declining or staying flat → Use the 90% current-year method. Paying 110% of a higher prior-year tax means unnecessarily tying up cash.
• Your income is highly variable → Consider the annualized income installment method (Section 3), which lets you adjust payments quarter by quarter.
• First year of 1099 income → You have no prior-year self-employment tax liability to base the 110% method on. Estimate current-year income conservatively and aim for 90%.

The annualized income installment method is tailor-made for locum physicians whose income fluctuates significantly from quarter to quarter. Instead of dividing your annual estimated tax into four equal payments, this method calculates each quarter's payment based on the income you actually earned during that period.

When to Use the Annualized Method

• You take locum assignments with gaps between them (earning $0 in some months and $50,000+ in others)
• You started your 1099 career mid-year
• You earn significantly more in certain seasons (e.g., holiday coverage)
• You have a large one-time income event (selling equipment, receiving a signing bonus)

How It Works: Step by Step

For each quarter, you calculate the tax as if your year-to-date income were annualized (multiplied to represent a full year), then figure the tax on that annualized amount, then take the appropriate fraction.

Example: Variable Locum Income

Dr. Kim earns the following locum income (after deductions) by quarter:

• Q1 (Jan–Mar): $120,000 (busy winter assignment)
• Q2 (Apr–May): $40,000 (took time off in April)
• Q3 (Jun–Aug): $100,000 (summer assignment)
• Q4 (Sep–Dec): $140,000 (holiday coverage, high rates)

Without the annualized method, Dr. Kim would need to estimate her full-year income ($400,000) and pay roughly $25,000 per quarter in estimated taxes—even in Q2 when she barely worked.

With the annualized method:

• Q1: Annualize $120,000 x 4 = $480,000. Tax on $480,000 ≈ $160,000. Q1 payment = 22.5% x $160,000 = $36,000
• Q2: Annualize $160,000 x 2.4 = $384,000. Tax on $384,000 ≈ $124,000. Cumulative = 45% x $124,000 = $55,800. Q2 payment = $55,800 - $36,000 = $19,800
• Q3: Annualize $260,000 x 1.5 = $390,000. Tax on $390,000 ≈ $126,000. Cumulative = 67.5% x $126,000 = $85,050. Q3 payment = $85,050 - $55,800 = $29,250
• Q4: Full year $400,000. Tax ≈ $128,000. Cumulative = 90% x $128,000 = $115,200. Q4 payment = $115,200 - $85,050 = $30,150

Federal estimated taxes are only part of the picture. Most states with income tax also require quarterly estimated payments, and if you work locums in multiple states, you may owe estimated taxes to several states simultaneously.

States With No Income Tax

Seven states have no individual income tax: Alaska, Florida, Nevada, South Dakota, Texas, Washington, and Wyoming. If you establish your tax home in one of these states, you eliminate state estimated tax payments for your home state entirely.

Multi-State Estimated Tax Obligations

When you work a locum assignment in a state with income tax, that state generally requires you to file a nonresident return AND may require estimated tax payments if your income from that state exceeds certain thresholds. Key considerations:

• Threshold amounts vary — Some states require estimated payments if you expect to owe $1,000+ in state tax; others have lower thresholds
• Due dates may differ from federal — Most states follow the federal quarterly schedule, but some have different dates
• Credits for taxes paid to other states — Your home state typically gives you a credit for taxes paid to other states, preventing double taxation
• Withholding by agencies — Some locum agencies withhold state taxes on your behalf. Check your pay stubs carefully

Strategy 1: The W-2 Withholding Hack

This is the single most powerful penalty avoidance strategy for physician couples. If your spouse (or you, if you also have W-2 income) has taxes withheld from a paycheck, that withholding is treated by the IRS as if it were paid evenly throughout the year—even if the withholding increase happens in December.

Why does this matter? Estimated tax payments are attributed to specific quarters. If you miss Q1, overpaying in Q4 doesn't eliminate the Q1 penalty. But W-2 withholding is spread evenly, so increasing withholding in Q4 effectively "covers" all four quarters retroactively.

How to Implement:

1. Calculate your total estimated tax liability for the year
2. Determine how much will be covered by estimated payments you've already made
3. Increase your (or your spouse's) W-2 withholding for the remaining paychecks to cover the shortfall
4. File a new Form W-4 with your employer to increase withholding

Strategy 2: Automate Your Estimated Payments

The most common cause of underpayment penalties isn't miscalculation—it's simply forgetting to make a payment. Set up automatic payments through EFTPS (Electronic Federal Tax Payment System) to ensure payments go out on time every quarter. Most state tax agencies also offer automatic payment options.

Strategy 3: The "Separate Account" Method

Open a dedicated savings account and automatically transfer 30–35% of every 1099 payment you receive into it. Use this account exclusively for tax payments. This approach ensures you always have the cash available when quarterly payments are due and prevents the common trap of spending tax money on living expenses.

Common Mistakes That Trigger Penalties

1. Forgetting Q2 is only 2 months — The Q2 payment (due June 15) covers only April and May, making it easy to miscalculate
2. Not adjusting for income spikes — A lucrative holiday locum assignment in Q4 can push you well past your estimated payments
3. Relying on year-end "catch up" — Making one large Q4 payment doesn't cover Q1–Q3 underpayments for estimated tax purposes
4. Ignoring state estimated taxes — Federal compliance doesn't protect you from state underpayment penalties
5. Using last year's income for a much higher-earning year — The 110% safe harbor helps, but if your income doubled, you may still owe a large balance at filing

Let's walk through a complete estimated tax calculation for a typical locum tenens physician. We'll calculate federal estimated payments using the 110% prior-year safe harbor method.

Meet Dr. Sarah Thompson

• Filing status: Married filing jointly
• Occupation: Locum tenens emergency medicine physician
• Expected 1099 income: $380,000
• Spouse: W-2 hospitalist earning $280,000 (withholding: $58,000)
• Tax home: Florida (no state income tax)
• Business structure: Sole proprietor (considering S-Corp)
• Prior year total tax liability: $145,000

Safe Harbor Calculation

110% of prior-year tax: $145,000 × 110% = $159,500

90% of current-year tax: $151,581 × 90% = $136,423

Dr. Thompson should use the 90% current-year method ($136,423) since it's lower than the 110% prior-year amount ($159,500). She needs to pay at least $136,423 through estimated payments and withholding.

Her spouse's W-2 withholding covers $58,000. So Dr. Thompson needs to make estimated payments of:

$136,423 – $58,000 = $78,423 in estimated payments

Divided into four equal quarterly payments: $19,606 per quarter

Payment Methods

• IRS Direct Pay (free) — Pay directly from your bank account at irs.gov/directpay. Instant confirmation.
• EFTPS (free) — Electronic Federal Tax Payment System. Requires enrollment but allows scheduled recurring payments.
• Credit/debit card (fees apply) — Processing fee of 1.85–1.98% for credit cards. Only worth it if you're earning rewards that exceed the fee.
• Check by mail — Mail Form 1040-ES voucher with a check. Slowest method; no instant confirmation.

How S-Corp Election Changes the Math

If Dr. Thompson from our walkthrough elected S-Corp status and paid herself a reasonable salary of $180,000, here's how the math changes:

The S-Corp saves Dr. Thompson approximately $9,500 in self-employment/payroll taxes annually because she only pays FICA on her $180,000 salary—not on the full $305,000 of net income. For more details on this strategy, see our S-Corp Election Guide.

Retirement Contributions Reduce Estimated Payments

Contributions to tax-deferred retirement plans directly reduce your taxable income and therefore your estimated tax payments. Here's the impact for Dr. Thompson:

For a comprehensive overview of all available deductions, visit our Physician Tax Deductions Guide.