Capital Gains Tax on a Colorado House Sale: Exclusion & Rates

Capital gains tax on a Colorado house sale usually comes to nothing for owner-occupiers, because federal law lets a single filer exclude up to $250,000 of gain on a primary residence and a married couple filing jointly exclude up to $500,000.¹ Any gain above that exclusion is taxed at the federal long-term capital gains rate and again by Colorado at its flat 4.40% income tax rate.²

Figuring Out Your Gain

Your gain is the net sale price minus your adjusted basis. The net sale price is what the buyer pays minus selling costs: agent commissions, title fees, attorney fees, and any transfer taxes you cover. Your adjusted basis starts with what you originally paid for the home and goes up by the cost of capital improvements you’ve made along the way.³

Improvements vs. Repairs

Only improvements raise your basis. An improvement adds value, extends the home’s useful life, or adapts it to a new use: adding a bathroom, replacing the roof, installing central air, building a deck, finishing a basement, putting in a new fence or driveway.⁴

Routine maintenance doesn’t count. Interior and exterior painting, patching cracks, fixing leaks, and replacing broken hardware are non-deductible repairs. One useful exception: if repair-type work is part of a larger remodeling project, it can be rolled into the improvement cost. Replacing a single broken window pane is a repair. Replacing every window in the house as part of an energy-efficiency overhaul is an improvement.⁴

Keep receipts and contractor invoices for every project. The difference between a $100,000 gain and a $60,000 gain can be the $40,000 kitchen renovation you can’t document.

The Primary Residence Exclusion

The Section 121 exclusion is the main reason most Colorado sellers owe no capital gains tax. Single filers exclude up to $250,000 of gain. Married couples filing jointly exclude up to $500,000. To qualify, you need to pass two tests during the five-year period ending on the sale date: you must have owned the home for at least two of those years, and you must have lived in it as your primary residence for at least two of those years. The two years don’t have to be consecutive.¹

For a married couple to get the full $500,000, both spouses must meet the use test, at least one must meet the ownership test, and neither spouse can have used the exclusion on another home sale within the past two years.¹ Because Colorado conforms to the federal treatment, anything excluded federally is also excluded from your Colorado taxable income. If your entire gain fits under the exclusion, you owe no state tax on the sale either.

Partial Exclusion for Early Sales

Sell before you’ve met the full two-year ownership or use requirement and you may still get a proportional exclusion if the sale was triggered by a change in employment location, a health condition, or certain unforeseen circumstances. Qualifying unforeseen events include divorce or legal separation, becoming eligible for unemployment compensation, the death of a spouse or co-owner, destruction or condemnation of the home, and giving birth to multiple children from the same pregnancy.⁴

The partial exclusion is prorated by the fraction of the two-year period you met. Fifteen months of ownership and use before a qualifying job relocation, for example, gets you 15/24 of the full $250,000 or $500,000.

Military and Foreign Service Extension

Members of the uniformed services or Foreign Service on qualified extended duty can elect to suspend the running of the five-year test period for up to 10 years, stretching the lookback window to 15 years. The election is made simply by excluding the gain on your return for the year of sale.⁵

The Depreciation Catch

If you claimed depreciation on part of the home because you rented out a room or took a home office deduction, the exclusion does not cover gain attributable to that depreciation taken after May 6, 1997. That portion is taxed as unrecaptured Section 1250 gain at a maximum federal rate of 25%, even though the rest of your gain qualifies for the exclusion.¹ This catches sellers off guard, particularly those who took a home office deduction for years without tracking the depreciation implications at resale.

Federal Rates on Gain Above the Exclusion

Gain above the Section 121 exclusion is taxed at the federal long-term capital gains rate if you owned the home for more than a year. For 2026, the rates are 0%, 15%, or 20%, depending on your overall taxable income.⁶ The approximate 2026 thresholds:

0% rate: taxable income up to about $49,450 single, $98,900 joint, $66,200 head of household.
15% rate: taxable income from those thresholds up to roughly $545,500 single, $613,700 joint, $579,600 head of household.
20% rate: taxable income above those ceilings.

Most Colorado homeowners with gain left after the exclusion land in the 15% bracket. The 0% rate shows up more often for retirees or people with a low-income year, and 20% typically affects only high earners. Owned the home a year or less? The gain is short-term and taxed as ordinary income at your marginal rate, a much worse outcome.

The 3.8% Net Investment Income Tax

Higher-income sellers face an additional 3.8% Net Investment Income Tax on the taxable portion of their gain. The NIIT kicks in when modified adjusted gross income exceeds $200,000 single, $250,000 married filing jointly, or $125,000 married filing separately. The surtax applies to the lesser of your net investment income or the amount by which your MAGI exceeds the threshold.⁷ It’s computed on Form 8960 and reported on your return.

Colorado’s 4.40% Tax on the Leftover Gain

Colorado taxes modified federal taxable income at a flat 4.40% as of the 2025 tax year, and that rate applies to capital gains the same as any other income.² The rate has moved recently (4.25% for 2024 before reverting to 4.40% for 2025), so confirm the rate for the year you actually sell. Only the gain that exceeds your federal Section 121 exclusion gets swept into your Colorado return.

Colorado does have a capital gains subtraction, but it almost certainly won’t help on a house sale. For tax years 2022 and later, the subtraction is limited to gains from the sale of agricultural land located in Colorado, acquired between May 9, 1994 and June 4, 2009, and held for at least five uninterrupted years.⁸ Residential property, rental property, and non-agricultural land don’t qualify.

Inherited or Gifted Homes Work Differently

How you got the property changes the math. Inherited homes get a “stepped-up basis”: your basis is generally the fair market value on the date the previous owner died, which wipes out decades of appreciation in one step.⁹ If the home was worth $450,000 when the owner passed and you sell it for $475,000, your taxable gain is $25,000, not the difference from a purchase price long ago.

Gifts work the opposite way. Your basis is the donor’s original basis plus any improvements they made, so you inherit their entire built-up gain. This is called carryover basis.¹⁰ If the home’s fair market value at the time of the gift was lower than the donor’s basis, you must use that lower fair market value as your basis when calculating a loss. Ask the donor for their purchase records and improvement documentation before they’re lost.

Reporting the Sale and Paying On Time

You must report a home sale on your federal return if the closing agent or title company issued you a Form 1099-S. The 1099-S triggers the reporting obligation even when the entire gain is excludable. The closing agent is only exempt from issuing the form if you provide written certification that the gain is fully excludable and the sale price is $250,000 or less, or $500,000 or less for a certified married seller.¹¹

Report the sale on Form 8949, listing the sale price, your adjusted basis, the gain, and the exclusion as a negative adjustment. The totals flow to Schedule D of Form 1040.

Estimated Tax Payments

A large taxable gain can create a bill that your paycheck withholding won’t cover. If you expect to owe more than $1,000 in net Colorado tax for the year after withholding and credits, you’re expected to make quarterly estimated payments to the Colorado Department of Revenue.¹² The IRS uses the same $1,000 threshold federally.

You can avoid the federal underpayment penalty by paying at least 90% of the current year’s tax liability or 100% of the prior year’s tax. If your AGI last year was above $150,000, that prior-year safe harbor rises to 110%.¹³ A $600,000 gain in a year where you normally earn $120,000 means regular withholding won’t come close. Making an estimated payment shortly after closing is the simplest way to stay ahead of penalties.

Rentals, Second Homes, and 1031 Exchanges

The Section 121 exclusion doesn’t apply to rental homes, vacation properties, or any real estate you didn’t use as a primary residence. The full gain is taxable, and two layers of federal tax often apply.

Depreciation claimed on a rental is taxed at a maximum federal rate of 25% as unrecaptured Section 1250 gain when you sell.¹⁴ The remaining gain above the depreciation amount is taxed at the standard long-term capital gains rate of 0%, 15%, or 20%.⁶ Colorado then taxes the entire gain at 4.40%. The NIIT applies to investment property gains too if your MAGI exceeds the thresholds.⁷ Stacked together, the effective rate on an investment property sale can approach 50% of the gain for high-income sellers.

A Section 1031 like-kind exchange lets you defer the entire capital gains tax by rolling the proceeds into another investment property. The timeline is strict: 45 calendar days from the sale to identify potential replacement properties in writing, and 180 calendar days to close.¹⁵ A qualified intermediary must hold the proceeds throughout the process; if you touch the money, the exchange fails. The replacement property must be held for investment or business use, not personal use.

Nonresident Withholding at Closing

If you’re not a Colorado resident and you sell Colorado real property for more than $100,000, the state requires withholding at closing of the lesser of 2% of the sale price or the net proceeds that would otherwise go to you.¹⁶ The title company sends the money to the Colorado Department of Revenue, and you claim it as a credit when you file your Colorado return. Any overpayment is refunded. It’s a prepayment mechanism, not an extra tax, but it reduces the cash you walk away with at closing.

1
Office of the Law Revision Counsel. 26 USC 121 – Exclusion of Gain From Sale of Principal Residence
2
Department of Revenue – Taxation. Individual Income Tax Guide
3
Internal Revenue Service. Property (Basis, Sale of Home, etc.) 3
4
Internal Revenue Service. Publication 523, Selling Your Home
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eCFR. 26 CFR 1.121-5 – Suspension of 5-Year Period for Certain Members of the Uniformed Services and Foreign Service
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Internal Revenue Service. Topic No. 409, Capital Gains and Losses
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Internal Revenue Service. Topic No. 559, Net Investment Income Tax
8
Colorado Department of Revenue. Income Tax Topics – Colorado Capital Gain Subtraction
9
Office of the Law Revision Counsel. 26 USC 1014 – Basis of Property Acquired From a Decedent
10
Office of the Law Revision Counsel. 26 USC 1015 – Basis of Property Acquired by Gifts and Transfers in Trust
11
Internal Revenue Service. Instructions for Form 1099-S (04/2025)
12
Cornell Law Institute. Colorado Code 39-22-605 – Estimated Tax Penalty
13
Internal Revenue Service. Underpayment of Estimated Tax by Individuals Penalty
14
Office of the Law Revision Counsel. 26 USC 1 – Tax Imposed
15
Office of the Law Revision Counsel. 26 USC 1031 – Exchange of Real Property Held for Productive Use or Investment
16
Colorado Department of Revenue. FYI Income 5 – Nonresident Real Estate Transactions – Required Withholding