What Happens If a Broker Reports a Different Basis Than Your Records?
Filing a tax return with a cost basis figure that doesn’t match what a broker separately reported to the IRS is the kind of small discrepancy that can trigger an outsized amount of correspondence later.
The short answer
If a crypto broker reports a cost basis to the IRS that differs from the basis you use on your own return, the mismatch can trigger an automated notice comparing the two figures, since the IRS receives the broker’s reported numbers independently of what you file. Resolving it typically means providing your own transaction records showing how you calculated basis, which is why keeping thorough, independent documentation matters even when a broker also reports on your behalf.
Why mismatches happen
Brokers report cost basis based only on the information available to them, which usually covers transactions that occurred entirely within their own platform. If crypto was purchased on one platform and later transferred to another before being sold, the receiving broker often has no reliable way to know the original purchase price, since tracking cost basis is widely recognized as one of the harder parts of crypto recordkeeping. In that situation, a broker may report a basis of zero or an estimated figure based only on when the asset arrived on its platform, which can be very different from the actual amount originally paid.
What a notice from the IRS typically looks like
When reported figures don’t match, the IRS commonly sends an automated notice pointing out the discrepancy and proposing an adjustment based on the broker’s reported numbers, which, if a broker reported an artificially low or zero basis, can significantly overstate the actual taxable gain. This isn’t necessarily an audit in the deeper sense; it’s often an automated comparison flagging a numeric mismatch that requires a documented response rather than an in-depth examination. Responding with clear, dated records is usually enough to resolve the discrepancy in the taxpayer’s favor when the taxpayer’s basis is accurate.
How to respond to a basis mismatch
- Gather your own transaction records. Purchase dates, prices paid, and any transfer history between platforms are the core evidence needed to support your reported basis.
- Identify why the mismatch occurred. Often it traces back to a transfer between platforms where the receiving broker lacked the original purchase information.
- Respond within the stated deadline. IRS notices typically specify a response window, and providing documentation promptly avoids the matter escalating further.
- Consider working with a tax professional. Since tax rules in this area continue to change and depend on individual circumstances, a professional can help make sure a response is complete and properly framed.
Why keeping independent records matters even with broker reporting
Broker reporting is meant to make tax compliance easier, but it isn’t a substitute for a taxpayer’s own records, particularly for anyone who moves crypto between platforms or uses self-custody wallets in between. Keeping a personal log of transaction dates, amounts, and prices at the time of each purchase is what actually resolves a mismatch quickly, since a broker’s incomplete information isn’t something a taxpayer can fix after the fact without evidence of their own.
The risks of not having documentation ready
Without independent records, a taxpayer may have little choice but to accept a broker’s inaccurate reported basis, potentially resulting in an overstated gain and a larger tax bill than actually owed. Reconstructing basis long after the fact, from memory or scattered exchange statements, is far harder than maintaining a running record from the start, and gaps in that reconstruction can leave real uncertainty about what was actually paid.
The takeaway
Broker reporting adds a layer of oversight to crypto tax compliance, but it’s only as accurate as the information a specific broker actually has, which is often incomplete once assets move between platforms. Maintaining independent, contemporaneous records is the most reliable way to resolve a basis mismatch quickly and support the figures reported on a tax return.