The Illinois capital gains tax is not a separate tax at all. Illinois folds capital gains into your ordinary income and applies its flat 4.95% individual income tax rate, whether you held the asset for two weeks or twenty years.1Illinois Department of Revenue. Income Tax Rates The federal preferential rates for long-term gains do not exist at the state level here, which is the detail that surprises most sellers.
The Flat 4.95% Rate and Why It Applies to Every Gain
Illinois starts its calculation with your federal adjusted gross income, makes certain modifications, and taxes the result at 4.95%.1Illinois Department of Revenue. Income Tax Rates Any capital gain that lands in your federal AGI — a stock sale, a rental property sale, a cryptocurrency trade — flows straight onto your Illinois return.
The federal system draws a sharp line at one year. Assets held one year or less produce short-term gains taxed as ordinary income; assets held longer produce long-term gains taxed at 0%, 15%, or 20% depending on income.2Internal Revenue Service. Topic No. 409, Capital Gains and Losses Illinois ignores the line entirely. So even when your long-term federal rate is 0%, Illinois still wants 4.95% of the gain.
Figuring the Gain
Your gain is your net sale price minus your basis. Basis usually starts with what you paid for the asset, plus acquisition costs like commissions, plus the cost of improvements. For real estate, that means capital improvements like a new roof; for stocks, it can include reinvested dividends. Selling costs come off the sale price before you subtract basis.
Depreciation makes rental real estate more complicated. Depreciation deductions you took over the years reduce your basis, and when you sell, the IRS recaptures that depreciation and taxes it at a federal rate of up to 25%. That recaptured amount sits inside your federal AGI, so Illinois taxes it at 4.95% along with everything else.
What Actually Reduces Your Illinois Bill
Almost every meaningful reduction happens at the federal level and flows through to Illinois because it never enters your AGI in the first place.
The Home Sale Exclusion
If you owned and lived in your home for at least two of the five years before selling, you can exclude up to $250,000 of gain, or up to $500,000 filing jointly if both spouses meet the use test.3Office of the Law Revision Counsel. 26 USC 121 – Exclusion of Gain From Sale of Principal Residence Because the excluded gain never reaches your federal AGI, it never reaches your Illinois return either. A married couple with $400,000 of gain on their home typically owes no Illinois tax on the sale.
Capital Losses
Losses offset gains dollar-for-dollar within the year. If your losses exceed your gains, you can deduct up to $3,000 of the net loss against other income ($1,500 if married filing separately), with the rest carried forward.4Office of the Law Revision Counsel. 26 USC 1211 – Limitation on Capital Losses The reduction reaches Illinois automatically through your AGI.
Qualified Small Business Stock
Stock in a qualifying domestic C corporation with under $50 million in assets at issuance, held more than five years, can qualify for a federal exclusion of up to 100% of the gain.5Office of the Law Revision Counsel. 26 USC 1202 – Partial Exclusion for Gain From Certain Small Business Stock Illinois follows the federal Internal Revenue Code on a rolling basis, so this exclusion passes through to your state return as well.6Illinois General Assembly. 35 ILCS 5/203 – Base Income Defined
Section 1031 Like-Kind Exchanges
Selling investment or business real estate and reinvesting the proceeds into similar property within the federal time limits defers the gain. You have 45 days to identify replacement properties and 180 days to close. The deferred gain never enters your federal AGI, so Illinois defers it too. A personal residence does not qualify. This is a deferral, not an exclusion: the gain lands on you when you eventually sell without exchanging.
Inherited Property vs. Gifted Property
These get treated very differently, and confusing them is expensive.
Inherited assets receive a stepped-up basis equal to the fair market value on the decedent’s date of death.7Office of the Law Revision Counsel. 26 USC 1014 – Basis of Property Acquired From a Decedent If a parent bought a house for $150,000 and it was worth $400,000 at death, your basis is $400,000. A sale at $400,000 produces no gain; a sale at $450,000 produces $50,000 of gain. Illinois follows the same basis, so the step-up cuts both taxes.
Inherited retirement accounts are an exception. Traditional IRAs and 401(k)s do not step up, and withdrawals are ordinary income to the heir at both the federal and Illinois levels.
Gifts carry the donor’s basis with them.8Office of the Law Revision Counsel. 26 USC 1015 – Basis of Property Acquired by Gifts and Transfers in Trust If a parent bought stock for $10,000 and gave it to you when it was worth $50,000, your basis is $10,000. Sell it for $55,000 and you owe tax on $45,000. Nothing about receiving the gift resets the clock the way an inheritance does. A separate rule limits loss transfers: if fair market value at the time of the gift was below the donor’s basis, your basis for computing a loss is that lower fair market value.
Non-Residents Who Sell Illinois Property
You can owe Illinois capital gains tax without living here. Gains from the sale of real property located in Illinois are allocated to Illinois regardless of the seller’s residence, including mineral interests like oil and gas.9Legal Information Institute (LII) / Cornell Law School. Allocation of Certain Items of Nonbusiness Income by Persons Other Than Residents – IITA Section 303
Non-residents file Form IL-1040 with Schedule NR to report Illinois-source income.10Illinois Department of Revenue. 2025 IL-1040 Instructions, Illinois Individual Income Tax The 2026 personal exemption is $2,925, phased out entirely once federal AGI exceeds $500,000 (joint) or $250,000 (all other statuses).11Illinois Department of Revenue. What Is the Illinois Personal Exemption Allowance? If your home state taxes the same gain, you generally claim a credit there for the Illinois tax paid, which prevents double taxation. The mechanics of that credit are set by your home state.
Filing and Deadlines
Capital gains land on Line 7 of Form IL-1040, pulled from your federal Form 1040. Attach your federal return and Schedule D.10Illinois Department of Revenue. 2025 IL-1040 Instructions, Illinois Individual Income Tax The filing deadline tracks the federal one: April 15, or the next business day when that falls on a weekend or holiday.
Illinois grants an automatic six-month extension to file, moving the deadline to October 15 for calendar-year filers with no separate form required.12Illinois Department of Revenue. Due Date/Extension to File Income Tax Return (2025 IL-1040) The extension covers filing, not paying. If you owe, you must pay by April 15 using Form IL-505-I to avoid penalties and interest.13Illinois Department of Revenue. Need More Time to File Your Tax Return? Here’s What You Need to Know
Estimated Payments on Large Gains
Investment income usually has no withholding. If you expect to owe more than $1,000 in Illinois tax after withholding and credits, you are required to pay quarterly estimates.14Illinois Department of Revenue. Pub-105, Estimated Payments Requirements For calendar-year individual filers, the due dates are:
- First quarter: April 15
- Second quarter: June 15
- Third quarter: September 15
- Fourth quarter: January 15 of the following year
A weekend or holiday pushes the due date to the next business day. The safe harbor from underpayment penalties is paying at least 90% of your current-year tax or 100% of last year’s tax in four equal installments.14Illinois Department of Revenue. Pub-105, Estimated Payments Requirements When gains are unpredictable, paying to last year’s number is the simpler route.
Penalties and Interest
Illinois charges separate penalties for filing late and paying late. The late-filing penalty is the lesser of $250 or 2% of the tax owed, reduced by timely payments and credits.15Illinois Department of Revenue. 2025 Form IL-2210 Instructions
The late-payment penalty starts at 2% of the unpaid tax if paid within 30 days of the due date and jumps to 10% after that.16Illinois Department of Revenue. Pub-103, Penalties and Interest for Illinois Taxes Paying whatever you can by April 15 is worth it even when you cannot pay in full.
Interest runs from the day after the due date until the balance is paid, calculated on a daily basis at a rate tied to the federal underpayment rate under IRC Section 6621 and reset twice a year.16Illinois Department of Revenue. Pub-103, Penalties and Interest for Illinois Taxes Unpaid balances after notice can be pursued through liens and levies.17Illinois Department of Revenue. Collection Process