When Victor sold a rental property he’d owned for fourteen years, he called his accountant in the spring expecting a straightforward conversation about the sale. What he got instead was a request for documentation going back to 2010 — purchase records, settlement statements, improvement receipts, and fourteen years of depreciation schedules.
Victor had assumed his old records didn’t matter anymore. Three years had passed since the earliest ones. He’d heard the IRS could only go back three years, so he’d stopped keeping most of his older paperwork.
His accountant explained something he’d never understood: the three-year audit window limits when the IRS can reopen old tax returns — but it doesn’t close the door on historical data that affects what you owe today. Victor’s gain calculation for the 2024 sale depended entirely on what he paid in 2010 and how much depreciation he’d taken over fourteen years. The IRS couldn’t audit 2010 directly. But it could absolutely ask him to prove his basis in 2024.
This distinction — between audit windows and documentation requirements — is what most investors miss entirely.
The standard rule: three years
For most returns filed accurately and completely, the IRS has three years from the filing date to initiate an examination and assess additional tax. File your 2023 return on April 15, 2024, and the standard window closes April 15, 2027.
This three-year rule covers the vast majority of ordinary investment situations — reported capital gains from stock sales, dividend income, interest, mutual fund distributions. When the data matches what brokerages reported and there are no substantial omissions, most investment-related issues are either caught quickly through automated matching or not at all.
In practice, automated mismatch notices — CP2000 letters from the IRS’s matching program — typically arrive within 12 to 24 months after filing, well inside the three-year window.
When the window extends to six years
The three-year window doubles to six years when the IRS determines that gross income was substantially understated — specifically, when the omitted amount exceeds 25% of the gross income reported on the return.
For investors, this rule has a nuance that often gets missed: it applies to gross proceeds, not net gain. If you sold stock for $120,000 with a $90,000 basis and a $30,000 gain, but didn’t report the sale at all, the IRS may see $120,000 in omitted gross proceeds — not just $30,000 in omitted gain. Whether that exceeds 25% of your total reported income depends on your specific numbers, but for large transactions relative to other income, the six-year window can apply even when the actual taxable gain was modest.
The six-year rule appears most often in cases involving unreported brokerage 1099-B sales, large cryptocurrency transactions that were never disclosed, foreign investment income, and major real estate transactions.
When there’s no time limit at all
Two situations remove the statute of limitations entirely. The first is a fraudulent return — one filed with intentional misrepresentation to evade tax. Fraud requires proof of deliberate intent, not just errors, and is relatively rare outside of significant criminal cases.
The second is more common than people realize: never filing a return. The three-year clock starts when a return is filed. If no return is filed, the clock never starts. An investor who had substantial capital gains in 2015 and simply didn’t file that year remains exposed to assessment indefinitely — even a decade later.
This is particularly relevant for cryptocurrency investors during the early years of the asset class, when reporting norms were unclear and many investors assumed crypto transactions didn’t need to be reported. Filing those years, even late, starts the clock. Not filing leaves them permanently open.
The critical distinction: audit windows vs. documentation requirements
This is the part Victor didn’t understand, and it’s where most long-term investors make a costly mistake.
The statute of limitations governs when the IRS can reopen a specific tax year and assess additional tax for that year. It does not govern your obligation to substantiate information that affects a current-year return.
When you sell an asset in 2024, the gain or loss on that sale depends on your cost basis — what you paid for the asset, adjusted for any improvements, depreciation, dividend reinvestments, or other factors. If you bought the asset in 2010, the IRS cannot audit your 2010 return. But it can absolutely require you to prove your 2010 purchase price when reviewing your 2024 return. If you can’t provide that documentation, it may calculate your gain using zero or an alternative basis, potentially resulting in a much larger taxable gain than actually occurred.
| Situation | IRS review window | Records needed until |
|---|---|---|
| Accurate return, all income reported | 3 years | 3 years after filing |
| Substantial income omission (25%+) | 6 years | 6 years after filing |
| Fraudulent return | Unlimited | Indefinitely |
| No return filed | Unlimited | Until filed + 3 years |
| Long-term stock/investment purchase | N/A for old year | Until asset is sold + 3 years |
| Rental property with depreciation | N/A for old years | Until property is sold + 3 years |
Real estate and the depreciation problem
Victor’s situation illustrates the most common long-term documentation issue in real estate. Rental property owners claim depreciation over 27.5 years for residential property. That annual deduction reduces both taxable income each year and the property’s adjusted basis. When the property is eventually sold, the IRS calculates gain based on the adjusted basis — original cost minus total depreciation taken.
If depreciation records are incomplete or lost, reconstructing them accurately is difficult. If the wrong depreciation amount is used, the gain calculation is wrong. And if accumulated depreciation was understated in prior years, there may be questions about whether the tax benefits those deductions generated were accurate — questions the IRS can raise in the sale year even though the individual depreciation years are closed.
Real estate investors should retain all purchase documentation, improvement records, and depreciation schedules for the entire ownership period plus the standard three years after the sale year’s return is filed.
Cryptocurrency and multi-year basis complexity
Crypto investors face the same fundamental issue in an even more fragmented context. A Bitcoin purchased in 2017, transferred between multiple wallets, partially sold in 2021, and partially sold again in 2024 requires documentation spanning seven years — even though only the most recent sales years may be within the standard audit window.
If records from 2017 are incomplete or the platform where the purchase was made has since closed, calculating accurate basis for the 2024 sale becomes difficult. Without basis, the gain defaults to the full sale proceeds. The statute of limitations offers no protection here because the IRS isn’t auditing 2017 — it’s asking you to prove the basis you’re claiming on your 2024 return.
Frequently asked questions
Does the three-year window mean I can discard investment records after three years? Only for records related purely to reporting on that year’s return. Records that establish the cost basis of assets you still hold must be kept until you sell those assets, plus the applicable audit window after the sale.
What if I can’t find records of a purchase I made fifteen years ago? Try to reconstruct it from available sources — old brokerage statements, bank records, email confirmations. If records are truly unavailable, document your best reasonable estimate and the steps you took to establish it. The absence of records doesn’t eliminate the tax obligation, but demonstrating a good-faith effort to substantiate basis is better than claiming zero.
Does filing an extension affect the three-year window? The window runs from the filing date. If you file on October 15 after an extension, the three-year window closes October 15 three years later — not April 15.