Most Illinois owners hear the same thing from another owner at some point:
“Have you looked into S-corp yet?”
It usually comes up around tax time, right after seeing what self-employment tax can do to a decent year.
The election can save you real money.
It can also cost you more than it’s worth if you switch too early.
The question worth sitting with isn’t whether an S-corp is a good idea in theory; it’s whether your numbers make it a good idea for you right now.
Here at Thompson Flaherty, we talk with clients about when should an Illinois business switch from sole prop or LLC to S-corp, and what we’re actually looking at when we run the comparison.
What’s the Actual Tax Difference Between a Sole Prop, LLC, and S-Corp?
For taxes, the main difference is how self-employment income gets treated. A sole proprietor and a single-member LLC taxed as a disregarded entity pay self-employment tax at 15.3% on all net profit.
An S-corp lets you split your income between a salary and distributions, and only the salary portion gets hit with payroll taxes.
The IRS requires S-corp owner-employees to pay themselves a “reasonable salary” before taking any distributions, so you can’t just set your salary at zero and take everything as a distribution.
The strategy works because distributions above that salary avoid the 15.3% self-employment tax, and in a strong year, that difference adds up quickly. Illinois charges a flat 4.95% individual income tax rate, which doesn’t change with the entity type, but the federal SE savings can still be significant.
What Income Level Makes the S-Corp Election Worth It in Illinois?
Most CPAs put the threshold somewhere between $50,000 and $80,000 in net self-employment income before an S-corp election starts making mathematical sense.
Below that range, the cost of running payroll, filing a separate corporate return (Form 1120-S), and paying an accountant to maintain the structure tends to eat up whatever tax savings you’d generate.
Let’s look at an example.
A client of ours was running a consulting business as a single-member LLC, clearing about $95,000 in net profit in 2024.
As a disregarded entity, she was paying self-employment tax on the full $95,000.
After we helped her elect S-corp status, set a reasonable salary of $55,000, and run proper payroll, her SE tax exposure dropped to just the salary portion. The tax savings covered the added cost of payroll administration and the corporate return with room to spare.
That’s not a promise of what you’d save, but it’s the math that makes the conversation worth having.
Reasonable Compensation Is Where the IRS Looks First
The IRS standard of “reasonable compensation“ is what an S-corp owner-employee must pay themselves as a salary, and it’s based on what you’d pay someone else to do the same job in the open market.
There’s no fixed number, but the IRS actively audits S-corps where owner salaries look artificially low relative to total distributions.
In practice, reasonable compensation varies a lot by industry.
A freelance graphic designer clearing $90,000 might set a salary around $50,000 to $60,000 based on comparable market rates.
A physician owner might need to set theirs much higher because the going rate for their specialty demands it.
The BLS Occupational Employment and Wage Statistics database is one defensible source for benchmarking what a given role pays. We use a few different tools when we’re helping a client set this up, and it’s worth doing carefully, because a salary that looks too low is an audit flag.
Our business tax planning work always includes a defensible salary analysis before we file.
Making the Election: Form 2553 and the March 15 Deadline
The S-corp election happens at the federal level by filing IRS Form 2553.
For an existing LLC, the entity stays in place as an LLC, but it elects to be taxed as an S-corp. Illinois doesn’t require a separate state-level election because Illinois follows the federal S-corp treatment automatically for most purposes.
The timing rules matter. To have S-corp status apply to a given tax year, you generally need to file Form 2553 by March 15 of that year (or within two months and 15 days of the start of the tax year for newly formed entities).
If you miss the deadline, you can sometimes get late election relief under IRS Revenue Procedure 2013-30, but it requires showing reasonable cause for the delay.
The short version: if you’re thinking about making this switch, earlier in the year is always better than later, and you don’t want to be calling us in October expecting it to apply to the current year.
The Ongoing Costs You’re Trading For the Tax Savings
The ongoing costs of S-corp status are real, and they’re why the election doesn’t make sense at low-income levels.
The main additions are payroll administration, quarterly payroll tax deposits, and a separate federal corporate return (Form 1120-S) plus an Illinois corporate return (Form IL-1120-ST).
Payroll processing for a single owner-employee typically runs $500 to $1,500 per year, depending on the provider and how frequently you run payroll.
The 1120-S return adds to your accounting fees compared to a Schedule C.
Illinois also requires S corporations to file Form IL-1120-ST and pay any applicable pass-through entity tax.
All in, the additional compliance cost for a small Illinois S-corp tends to run $1,500 to $3,500 per year, depending on complexity. That’s the floor you need to clear in tax savings before the switch makes sense.
Can an LLC Stay an LLC and Still Be Taxed as an S-Corp?
Yes, and for most owners we work with in Metro East, that’s exactly how we set it up.
You keep the LLC operating agreement, the limited liability protection, and the simpler state-level maintenance of an LLC, while electing to have the IRS treat the entity as an S-Corp for federal tax purposes.
One thing to watch: once you make the S-corp election, there are restrictions on ownership.
S-corps can have no more than 100 shareholders, all shareholders must be US citizens or resident aliens, and certain entity types (like partnerships and most corporations) cannot be shareholders. For a solo owner or a two-partner operation, none of that is a practical concern.
But if you’re planning to bring on investors or restructure ownership in the future, it’s worth knowing the constraints before you elect.
Clean, well-maintained books also become more important once you’re running payroll and distributing profits, which is one more reason year-round accounting tends to save money over the long run.
Signs You’ve Already Waited Too Long
The clearest sign is consistently paying more than $7,000 to $10,000 per year in self-employment tax on income above what a reasonable salary would be.
That’s money going to FICA on earnings that, as an S-corp owner, wouldn’t be subject to payroll taxes. If you’ve had two or three strong years as a sole prop or LLC and your net income is reliably above the $80,000 to $100,000 range, you’ve likely been leaving money on the table.
Another signal: your business income is starting to look consistent enough to forecast.
The S-corp structure works best when you can run a regular, predictable payroll. If your income swings wildly from month to month, payroll compliance gets more complicated, and the risk of underpaying quarterly payroll taxes goes up.
The owners who benefit most from the switch are the ones who’ve moved from scrappy and variable to stable and growing.
How the Illinois PTE Tax Changes the Math
Illinois has a flat individual income tax rate of 4.95% and a corporate income tax rate of 9.5%. For S-corps, the income passes through to the owners and gets taxed at the individual rate, not the corporate rate, so the pass-through structure is still favorable for most owners in Illinois.
Illinois also allows S-corps to pay a Pass-Through Entity (PTE) tax at the entity level and claim a corresponding credit for owners. This can be a useful workaround for the federal $10,000 cap on state and local tax (SALT) deductions.
Depending on your situation, paying the Illinois PTE tax and taking the full deduction at the entity level may save more at the federal level than what it costs at the state level. It’s not a slam dunk for everyone, but it’s a planning conversation worth having if your Illinois tax bill is significant.
That’s the kind of multi-layer Illinois tax strategy we work through with clients every year.
If you’re at the point where you’re asking whether an S-corp makes sense for your business, that’s usually a sign the conversation is worth having.
We sit down with Metro East and St. Louis owners year-round to run the numbers and figure out whether the structure matches the income.
If you’re ready to look at what the switch would actually mean for your tax bill, reach out to us at Thompson Flaherty, and we’ll walk through it together.
Until next time!
