Quarterly Estimated Taxes for 1099 Contractors: 2026 Due Dates, Safe Harbor, and Illinois Rules

Short answer: If you expect to owe $1,000 or more for 2026 after withholding, you generally must pay estimated tax. The 2026 federal due dates are April 15, June 15, and September 15, 2026, and January 15, 2027. To avoid the penalty, pay 90% of your 2026 tax or 100% of your 2025 tax (110% if 2025 AGI topped $150,000).

No one withholds tax from a 1099 check. If you're a locum physician, NP, PA, CRNA, or any other independent contractor, you pay your income tax and self-employment tax yourself during the year with Form 1040-ES. Illinois works the same way with Form IL-1040-ES. This guide covers the 2026 dates, how much to pay, what changes after an S-Corp election, and the Illinois rules. All figures come from the IRS and the Illinois Department of Revenue (links in Sources).

2026 estimated tax due dates (Form 1040-ES)

The IRS splits the year into four payment periods. They aren't equal quarters.

Source: Form 1040-ES (2026) and Publication 505 (2026), Table 2-1.

• Weekends and holidays. If a due date falls on a Saturday, Sunday, or legal holiday, the payment is on time if you make it the next business day (Publication 505). None of the four 2026 dates do: April 15, 2026 is a Wednesday, June 15 is a Monday, September 15 is a Tuesday, and January 15, 2027 is a Friday.
• Skipping the January payment. You don't have to make the January 15, 2027 payment if you file your 2026 return by February 1, 2027 and pay the whole balance with it (Form 1040-ES). January 31, 2027 is a Sunday, so the form uses Monday, February 1.
• More than four payments is fine. You can pay weekly, every two weeks, or monthly, as long as you've paid enough by each due date (IRS estimated taxes page). That suits locum work, where pay comes in uneven chunks.
• Mailed payments. A U.S. postmark by the due date counts as on time. The 2026 Form 1040-ES warns that the postmark date is the date USPS processes the mail at a facility, which may be later than the day you drop it off.

If you start 1099 work partway through 2026

You don't owe a payment for a period before you had income subject to estimated tax. Publication 505 sets out when your first payment is due:

This matters if you finished residency or fellowship in June and started locums in July. Your first 2026 payment was due September 15, 2026. If your income starts after March 31, the 2026 Form 1040-ES points you to the annualized income installment method (covered below).

Who has to make estimated tax payments (the $1,000 rule)

Under the 2026 Form 1040-ES, you generally must pay estimated tax if both of these apply:

1. You expect to owe at least $1,000 for 2026 after subtracting withholding and refundable credits.
2. You expect your withholding and refundable credits to be less than the smaller of 90% of your 2026 tax or 100% of your 2025 tax (110% for higher earners; see the next section).

The IRS says this applies to sole proprietors, partners, and S corporation shareholders (IRS estimated taxes page). Estimated tax covers more than income tax: it also covers self-employment tax and alternative minimum tax.

Exception: You don't have to pay 2026 estimated tax if you were a U.S. citizen or resident alien for all of 2025 and had no tax liability for the full 12-month 2025 tax year (Form 1040-ES). This can apply to a new attending whose 2025 tax was zero, but most physicians coming out of training had some 2025 tax.

If you also have a W-2 job, you can skip some or all estimated payments by asking that employer to withhold more. File a new Form W-4 and enter the extra amount on the line for additional withholding (IRS estimated taxes page).

How much to pay: the safe harbor rules (90%, 100%, 110%)

You won't owe an underpayment penalty if your withholding plus timely estimated payments add up to at least the smaller of these amounts:

• The $150,000 AGI line is $75,000 if you're married filing separately for 2026 (Form 1040-ES).
• The prior-year safe harbor only works if your 2025 return covered all 12 months.
• Under the regular method, you pay one-fourth of the required annual amount by each due date (Publication 505).
• Owing less than $1,000 at filing time also keeps you clear of the penalty (IRS Topic 306).

Which one should you use? The prior-year number is fixed and already on your 2025 return, so you know it in advance. The 90% number depends on a guess about 2026 income, which is hard to pin down with locum work, sign-on bonuses, or a new contract partway through the year. If your income is rising, 110% of last year's tax is usually the easy, predictable choice. If your income is dropping, 90% of this year's tax may mean smaller payments. You can switch at any time by redoing the 2026 Estimated Tax Worksheet (IRS estimated taxes page).

Retirement contributions change the math too. Pre-tax Solo 401(k) contributions lower the income tax part of your estimate. See Solo 401(k) contribution limits for 2026.

Not sure which safe harbor fits your year? Run your numbers in the free IndieVaults tax savings calculator, or get a free tax analysis and we'll go through it with your CPA.

The underpayment penalty (Form 2210)

If you didn't pay enough by any due date, you can owe a penalty for that period, even if you get a refund when you file (IRS estimated taxes page). You figure it on Form 2210.

• How it's figured. The penalty applies to each late or short installment, for the number of days it stays unpaid (Form 1040-ES). The Form 2210 worksheet multiplies the underpayment by the days late and by the IRS underpayment interest rate (Instructions for Form 2210, 2025).
• 2026 rates. The IRS underpayment rate is 7% for January–March, 6% for April–June, 7% for July–September, and 7% for October–December 2026 (IRS quarterly interest rates).
• What that means in dollars. A $17,000 installment paid 92 days late at 7% costs about $300 ($17,000 × 7% × 92 ÷ 365).
• Waivers are narrow. The IRS can waive the penalty if the underpayment came from a casualty, disaster, or other unusual circumstance, or if you retired after age 62 or became disabled during the year or the year before and had reasonable cause (IRS estimated taxes page). The IRS says the penalty generally can't be waived for reasonable cause alone.

Missed the first three 2026 payments? Pay what you owe as soon as you can. The penalty runs per installment and per day, so paying now stops it from growing on the missed amounts. Then make the January 15, 2027 payment, or file and pay in full by February 1, 2027.

Uneven income? The annualized income installment method

The regular method assumes you earn evenly all year. If most of your income comes late in the year (for example, a big fall locum block or a contract that starts in July), the annualized income installment method can lower or eliminate the earlier required payments (Form 1040-ES; Publication 505, chapter 2).

It works by measuring your actual income through the end of each period and scaling it up to a full year:

Source: Publication 505 (2026), Worksheet 2-9 (annualization amounts and applicable percentages).

• You must attach Form 2210 with Schedule AI to your return if you use this method, even if you don't owe a penalty (Form 1040-ES).
• If you use Schedule AI for any payment due date, you must use it for all of them (Instructions for Form 2210).
• Your self-employment tax is annualized separately on the same schedule.
• Good records help: you'll need income and deductions by period, not just for the year.

Estimated taxes after an S-Corp election

An S-Corp election changes how you pay during the year more than whether you pay. Here's what moves where:

Your salary. The S-Corp withholds federal income tax, Social Security, and Medicare from your W-2 pay and deposits it through payroll. Illinois withholding on wages is 4.95% of net income under the state's withholding rules (IL DOR income tax rates).

Your K-1 profit. Profit that passes through to you on Schedule K-1 has no withholding, and it isn't subject to self-employment tax (see how S-Corp status reduces self-employment tax). You still owe income tax on it. The IRS says S corporation shareholders generally have to make estimated payments if they expect to owe $1,000 or more (IRS estimated taxes page).

The withholding advantage. For the penalty calculation, federal income tax withheld from wages is treated as paid one-fourth on each due date unless you choose to show otherwise (Instructions for Form 2210, 2025). Estimated payments count only on the date you make them. So an S-Corp owner who's behind in the fall can raise the federal withholding on the last payrolls of the year, and that withholding gets spread back across all four periods. Many S-Corp owners do one of these:

• Withholding only: set extra withholding on your W-4 high enough to cover the K-1 income tax.
• Withholding plus estimates: normal withholding on salary, plus 1040-ES payments for the K-1 tax.
• Year-end true-up: pay estimates during the year, then fix any shortfall with extra withholding in December.

Your first S-Corp year. The safe harbor still uses your 2025 total tax, which may include a full year of self-employment tax as a sole proprietor. That can make 110% of last year's tax higher than you need, which is one reason to rerun the 90% figure once payroll is set up. If you haven't elected yet, start with our S-Corp election guide and LLC vs. S-Corp for 1099 contractors.

Illinois credits. The IL-1040-ES worksheet subtracts pass-through withholding and the pass-through entity tax credit before you test the $1,000 threshold (IL-1040-ES, 2026). If your S-Corp pays Illinois pass-through entity tax, have your CPA include that credit when sizing your Illinois estimates. The S-Corp's own 1.5% Illinois replacement tax (IL DOR income tax rates) is a company tax, separate from your IL-1040-ES.

Thinking about an S-Corp and wondering how payroll would change your estimates? See the numbers for your profit level in the IndieVaults calculator, or book a free tax analysis.

Illinois estimated tax payments (IL-1040-ES)

Illinois residents make separate state estimated payments with Form IL-1040-ES.

• Who must pay. You must make Illinois estimated payments if you reasonably expect your 2026 Illinois tax to be more than $1,000 after subtracting Illinois withholding, pass-through withholding, and credits such as income tax paid to other states, the Illinois property tax credit, and the pass-through entity tax credit (IL-1040-ES, 2026). The IL DOR adds that you'll likely need to pay if your income is partly or fully exempt from Illinois withholding, which describes 1099 income.
• How the estimate works. The worksheet takes your expected Illinois base income, subtracts your exemption allowance, multiplies by 4.95%, and divides by four (IL-1040-ES, 2026). The exemption allowance was $2,850 for 2025, and it isn't allowed if federal AGI is over $250,000 ($500,000 married filing jointly) (2025 IL-1040 Instructions). For 2026, the exemption allowance is $2,925 (IL DOR Informational Bulletin FY 2026-15).
• Due dates. April 15, 2026, June 15, 2026, September 15, 2026, and January 15, 2027 (IL-1040-ES, 2026). If a date falls on a weekend or holiday, use the next business day (IL-2210 Instructions).
• Safe harbor. The IL DOR waives the estimated tax penalty if you paid the lesser of 100% of last year's tax or 90% of this year's tax on time (IL-2210 Instructions; IL-1040-ES). Illinois forms don't include a 110% rule for high earners.
• Penalty. Illinois charges a late-payment penalty of 2% if a payment is 1–30 days late and 10% if it's 31 or more days late (IL DOR Publication 103).
• Uneven income. Illinois has its own annualization on Form IL-2210. If you annualize, you must do it for all four installments (IL-2210 Instructions).
• How payments are applied. The IL DOR applies each payment to the earliest due date until that one is paid, unless you tell it otherwise (IL-1040-ES).

How to pay estimated taxes (Direct Pay, Online Account, EFTPS)

Federal options (Form 1040-ES, 2026; IRS payment pages):

• IRS Online Account: make estimated payments and see your payment history in one place.
• IRS Direct Pay: free transfers from your checking or savings account. Choose "estimated tax" and tax year 2026.
• EFTPS: free, and it lets you schedule payments up to 365 days ahead. However, the IRS now says individual taxpayers can no longer create new EFTPS accounts. Current users can keep using it for now, and new individual payers are pointed to their Online Account or Direct Pay (IRS EFTPS page). EFTPS is still relevant for business tax deposits, including some S-Corp payroll taxes.
• Debit card, credit card, or digital wallet: available through IRS-approved processors, who charge a fee.
• Check or money order: mail it with the 2026 Form 1040-ES voucher, payable to "United States Treasury," with "2026 Form 1040-ES" and your SSN on it.
• Overpayment credit: you can apply part or all of a 2025 refund to your 2026 estimated tax (Publication 505).

Illinois options (IL-1040-ES, 2026):

• MyTax Illinois: pay from your checking or savings account. You need your IL-PIN.
• Credit card: the processor charges a convenience fee.
• Electronic funds transfer: sign up with Form EFT-1.
• Check: mail it with the IL-1040-ES voucher. If you pay electronically, don't send the voucher.

Worked example: a $250k locum physician (illustrative)

Illustrative only. This simplified, hypothetical example shows how the 2026 rules fit together. It assumes single filing status, the standard deduction, no other income, no retirement contributions, no credits, and no qualified business income (QBI) deduction. A physician's QBI deduction may be limited or unavailable at this income level, so ask your CPA. It isn't a recommendation of what you should pay.

Facts (hypothetical): Dr. A is a single locum hospitalist who lives in Illinois. All work is on 1099s. Expected 2026 net profit after business expenses is $250,000. Dr. A's 2025 AGI was $200,000 and 2025 total tax was $64,000 (assumed).

Step 1: Estimate 2026 federal tax.

Where the numbers come from: the 92.35% factor and the $184,500 Social Security wage base are on the 2026 Form 1040-ES. The 0.9% Additional Medicare Tax applies above $200,000 for single filers (IRS SE tax page). The AGI line subtracts half of the regular SE tax ($29,573 ÷ 2 = $14,787). The $16,100 single standard deduction and the Schedule X brackets come from the 2026 Form 1040-ES. Income tax is $41,024 + 32% × ($219,113 − $201,775).

Step 2: Pick the safe harbor. Dr. A's 2025 AGI was over $150,000, so the prior-year option is 110%.

The smaller required amount is $68,781 (90% of the 2026 estimate), but it's only safe if the $250,000 projection holds. If Dr. A picks up extra shifts and ends up earning more, payments based on 90% of the old projection could fall short. Paying $17,600 a quarter (110% of 2025 tax) protects Dr. A from the federal penalty no matter how high 2026 income goes. Any extra comes back as a refund or a credit toward 2027.

Step 3: Illinois. Assuming Illinois base income equals federal AGI, Illinois tax is about ($235,213 − $2,925 exemption) × 4.95% = $11,498. That's about $2,875 per quarter on IL-1040-ES. Because Illinois' prior-year safe harbor is 100%, Dr. A could instead pay 100% of the 2025 Illinois tax.

Step 4: It's October 1 and Dr. A hasn't paid anything. The April, June, and September installments are already late, and the federal penalty grows daily on each one at the 7% Q4 2026 underpayment rate. Dr. A should pay the missed federal and Illinois amounts now, then make the January 15, 2027 payments. For Illinois, payments 31 or more days late already fall in the 10% penalty tier (IL DOR Publication 103).

Same doctor with an S-Corp (no numbers): If Dr. A ran the work through an S-Corp and took a reasonable W-2 salary, payroll would withhold federal and Illinois tax from that salary. Dr. A would cover the tax on K-1 profit with 1040-ES and IL-1040-ES payments or extra W-2 withholding. Because federal wage withholding is treated as paid evenly through the year, a December withholding increase could fix an earlier shortfall. Estimated payments can't do that.

Want your own version of this table? Use the free IndieVaults calculator, or request a free tax analysis. We work alongside your existing CPA.

Common mistakes

1. Using 100% of last year's tax when your AGI was over $150,000. For 2026, the prior-year safe harbor is 110% if your 2025 AGI topped $150,000 ($75,000 married filing separately).
2. Thinking a refund means no penalty. The penalty is figured per installment. You can owe it even if you're due a refund at filing.
3. Treating the quarters as equal. The second period covers only April and May, and the fourth payment is due in January of the next year.
4. Forgetting self-employment tax. Estimated tax covers SE tax as well as income tax. At $250,000 of 1099 profit, SE tax alone is about $29,600.
5. Skipping Illinois. IL-1040-ES is separate from Form 1040-ES, has its own $1,000 test, and its late-payment penalty jumps to 10% after 30 days.
6. Assuming an S-Corp ends estimated taxes. Payroll handles tax on your salary, not on K-1 profit, unless you raise your withholding to cover it.
7. Not adjusting after a big change. A new contract, a sign-on bonus, or a mid-year S-Corp election means you should redo the worksheet before the next due date.
8. Using the annualized method without Schedule AI. You must attach Form 2210 with Schedule AI, even if no penalty is due.
9. Counting on EFTPS as a new user. Individuals can't open new EFTPS accounts. Use your IRS Online Account or Direct Pay.
10. Mailing a check on the due date. The postmark is the date USPS processes it, which may be later than the day you mail it. Pay electronically, or mail early.

Frequently asked questions

When are 2026 quarterly estimated taxes due?

For 2026 income, federal Form 1040-ES payments are due April 15, 2026, June 15, 2026, September 15, 2026, and January 15, 2027. None of those dates falls on a weekend or holiday. You can skip the January payment if you file your 2026 return by February 1, 2027 and pay the full balance. Illinois IL-1040-ES uses the same four dates.

Do 1099 contractors have to pay quarterly estimated taxes?

Usually, yes. Under the 2026 Form 1040-ES, you generally must pay estimated tax if you expect to owe at least $1,000 after withholding and refundable credits, and your withholding won't cover the safe harbor amount. Nothing is withheld from 1099 income, so most contractors with meaningful profit need to pay. Estimated tax covers income tax and self-employment tax.

What is the estimated tax safe harbor if my income is over $150,000?

You avoid the federal penalty by paying the smaller of 90% of your 2026 tax or 110% of your 2025 tax, if your 2025 AGI was more than $150,000 ($75,000 if married filing separately for 2026). Below that AGI, the prior-year figure is 100%. Pay the amount in four equal installments by the due dates unless you use the annualized method.

What is the penalty for underpaying estimated taxes?

The IRS figures the penalty on Form 2210 for each installment that was late or short, for the number of days it stayed unpaid, at the IRS underpayment interest rate. That rate is 7% for October through December 2026. You can owe the penalty even if you get a refund. Illinois charges a separate 2% or 10% late-payment penalty.

I missed the first three 2026 estimated payments. What should I do now?

Pay the missed amounts as soon as you can. The federal penalty is figured per installment and per day, so paying now stops it from growing. Then make the January 15, 2027 payment, or file and pay in full by February 1, 2027. If your income came mostly late in the year, the annualized income installment method on Form 2210, Schedule AI, may reduce the penalty.

Do S-Corp owners still have to make estimated tax payments?

Often, yes. Payroll withholds tax from your W-2 salary, but nothing is withheld from your K-1 profit, and the IRS says S corporation shareholders generally must pay estimated tax if they expect to owe $1,000 or more. You can cover it with Form 1040-ES payments or by raising your W-2 withholding. Wage withholding is treated as paid evenly through the year.

Does Illinois require estimated tax payments?

Yes, if you reasonably expect your 2026 Illinois tax to be more than $1,000 after Illinois withholding, pass-through withholding, and credits. You pay with Form IL-1040-ES on the same four dates as the federal payments. The rate is 4.95% of net income. Illinois waives the penalty if you paid on time the lesser of 90% of this year's tax or 100% of last year's tax.

Can I still pay estimated taxes through EFTPS?

Only if you already have an account. The IRS says individual taxpayers can no longer create new EFTPS accounts, though current users can keep using it for now. New individual payers can use their IRS Online Account or IRS Direct Pay, which are free from a bank account. For Illinois, use MyTax Illinois.

Plan your 2026 estimates

Want to see how S-Corp payroll, Solo 401(k) contributions, and safe harbor choices would change your quarterly payments? Try the free IndieVaults tax savings calculator. Or book a free tax analysis, and we'll go through it with your existing accountant. You can also reach us at hello@indievaults.com or (773) 617-5359.

Related guides

• Self-Employment Tax: How It Works and How to Reduce It Legally
• S-Corp Election for Independent Contractors
• LLC vs. S-Corp for 1099 Contractors
• Solo 401(k) Contribution Limits for 2026
• Solo 401(k) vs. SEP-IRA

Sources

• IRS, Form 1040-ES (2026), Estimated Tax for Individuals (who must pay, safe harbor, 110% rule, due dates, February 1, 2027 filing exception, postmark caution, payment methods, 2026 tax rate schedules, standard deduction, $184,500 Social Security wage base): https://www.irs.gov/pub/irs-pdf/f1040es.pdf
• IRS, Publication 505 (2026), Tax Withholding and Estimated Tax (Table 2-1 due dates, weekend and holiday rule, first-payment table, annualization amounts and applicable percentages, overpayment credit): https://www.irs.gov/pub/irs-pdf/p505.pdf
• IRS, "Estimated taxes" (who must pay, including S corporation shareholders; more than four payments; Form W-4 extra withholding; penalty waivers): https://www.irs.gov/businesses/small-businesses-self-employed/estimated-taxes
• IRS, Topic no. 306, Penalty for underpayment of estimated tax: https://www.irs.gov/taxtopics/tc306
• IRS, "Underpayment of estimated tax by individuals penalty": https://www.irs.gov/payments/underpayment-of-estimated-tax-by-individuals-penalty
• IRS, Instructions for Form 2210 (2025) (withholding treated as paid one-fourth on each due date; penalty worksheet; Schedule AI): https://www.irs.gov/pub/irs-pdf/i2210.pdf
• IRS, "Quarterly interest rates" (2026 underpayment rates: 7%, 6%, 7%, 7%): https://www.irs.gov/payments/quarterly-interest-rates
• IRS, "Direct Pay with bank account": https://www.irs.gov/payments/direct-pay-with-bank-account
• IRS, "EFTPS: The Electronic Federal Tax Payment System" (no new individual enrollments): https://www.irs.gov/payments/eftps-the-electronic-federal-tax-payment-system
• IRS, "Self-employment tax (Social Security and Medicare taxes)" (Additional Medicare Tax thresholds): https://www.irs.gov/businesses/small-businesses-self-employed/self-employment-tax-social-security-and-medicare-taxes
• Illinois Department of Revenue, Form IL-1040-ES (2026), Estimated Income Tax Payments for Individuals: https://tax.illinois.gov/content/dam/soi/en/web/tax/forms/incometax/documents/currentyear/individual/il-1040-es.pdf
• Illinois Department of Revenue, "Income Tax Rates" (4.95% individual rate; 1.5% replacement tax for S corporations): https://tax.illinois.gov/research/taxrates/income.html
• Illinois Department of Revenue, 2025 Form IL-1040 Instructions (exemption allowance and income limits): https://tax.illinois.gov/content/dam/soi/en/web/tax/forms/incometax/documents/currentyear/individual/il-1040-instr.pdf
• Illinois Department of Revenue, 2025 Form IL-2210 Instructions (safe harbor waiver, annualization, weekend rule): https://tax.illinois.gov/content/dam/soi/en/web/tax/forms/incometax/documents/currentyear/individual/il-2210-instr.pdf
• Illinois Department of Revenue, Publication 103, Penalties and Interest for Illinois Taxes (2% and 10% late-payment penalty): https://tax.illinois.gov/content/dam/soi/en/web/tax/research/publications/pubs/documents/pub-103.pdf

Disclaimer

This guide is for general educational purposes only and is not tax, legal, or investment advice. The worked example is hypothetical and illustrative, and it leaves out deductions and credits that may apply to you, including the QBI deduction and retirement contributions. Due dates, safe harbor rules, and rates are the 2026 figures published by the IRS and the Illinois Department of Revenue as of the date modified above, and rules can change. Some Illinois figures come from 2025 instructions where 2026 versions weren't yet available. Before you set or change your estimated payments, check with your CPA or tax advisor. IndieVaults works alongside your existing accountant and doesn't replace one.