Last updated October 24, 2026.

Why Your Crypto Cost Basis Is Probably Wrong (2026)

The Alt Desk · Rails · Checked against official sources, October 2026 · Educational only, not financial advice

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Ask most crypto holders what a coin is worth and they'll tell you to the cent. Ask what they paid for it and you get a rough number from memory. That number is your cost basis, and it decides how much gain you report when you sell.

For US tax purposes, digital assets are property, not currency.^[2] So the same basic rule applies as with any property: gain or loss is what you received minus your adjusted basis.^[1] If the basis is wrong, the gain is wrong. Usually it's wrong in a way that costs you.

Here are the four places basis goes wrong most often, and a short check you can run tonight.

The 20-minute basis check

Pick your single largest holding. Then answer four questions for it:

1. Do I know every purchase, with date, units and price?
2. Did I add the fees I paid to buy each lot?
3. Did any of these units come from a swap, a reward, or a transfer from another wallet?
4. Do I know which wallet or account each lot sits in today?

If you can't answer all four, that holding's basis is a guess. The sections below show what each gap does to the number.

Leak 1: you left out the fees

The IRS says your basis is what you spent to acquire the coin, including fees, commissions and other acquisition costs.^[1] Exchange screens often show the coin price and the fee on separate lines. People write down the first and forget the second.

Made-up example. You buy 2 units of a coin for $1,000 and pay a $15 fee. Your basis is $1,015, not $1,000. Later you sell both units for $1,300. On these example numbers the gain is $285, not $300.

Fifteen dollars looks small. Across a few years of small, frequent buys, the missing fees can add up to real money. And every missing dollar of basis is a dollar of gain you report that you didn't actually make.

Leak 2: you treated a swap as a non-event

Trading one coin for another feels like moving money around. The IRS treats it as disposing of the first coin. You recognize a gain or loss on it, and the coin you receive starts with a basis equal to its fair market value at the time of the swap.^[1]

Made-up example. You bought Coin A for $500. Months later you swap it for Coin B when your Coin A is worth $900. That swap is a $400 gain on Coin A, even though no dollars hit your bank. Your basis in Coin B is $900, not $500.

Miss the swap and you make two mistakes at once. You skip a gain you should have reported. And you carry the wrong basis into Coin B, so the next sale is wrong too.

Leak 3: you moved coins between your own wallets

Moving coins from an exchange to your own wallet, or between two wallets you own, is generally not a taxable event.^[1] That part is good news. Two details make it messy.

The fee. The IRS says a transfer between your own wallets is not a digital asset transaction, unless you paid the transaction fee with digital assets. Paying the fee in crypto counts as a transaction.^[2] So the network fee on a self-transfer is its own small event to log.

The history. The receiving wallet knows nothing about what you paid. If you don't carry the purchase records across, those units arrive with no visible basis. Years later, when you sell from that wallet, it can look like the whole amount is gain.

This matters more now. Starting January 1, 2025, the IRS rules track basis wallet by wallet, or account by account, instead of across everything you own. Rev. Proc. 2024-28 gave holders a way to assign their unused basis to each wallet and account as of that date.^[2][4] If you never did that exercise, it's worth asking a tax pro about it.

Leak 4: you forgot the rewards, and the forms won't save you

Coins you receive from staking, mining or similar activity are income, reported when you receive them.^[2] Write down the date and the US dollar value on that day. You need it for the income line now and for the basis of those coins later.

Then there's Form 1099-DA. US brokers must report gross proceeds for digital asset sales made on or after January 1, 2025, and basis on certain sales made on or after January 1, 2026.^[2] That sounds like the broker will do the work for you. It won't do all of it:

• For 2025, the filing rules generally apply to US brokers. A foreign exchange may not send you a 1099-DA.^[3]
• The rules don't cover non-custodial wallets and other brokers that never hold your coins.^[2]
• A broker can only report basis it knows about. Coins you moved in from somewhere else arrive with no history on its side.

The IRS is clear that you must report all digital asset income, gains and losses whether or not you get a 1099-DA, and that you must work out basis before you file.^[3] The form is a starting point, not your records.

Which units did you sell?

One more quiet leak. If you hold the same coin bought at different prices, the units you count as sold change the gain. Under the IRS FAQ for earlier years, you can pick specific units only if you can identify them and prove their basis. If you don't, the default is first in, first out.^[1] The rules for 2025 and later add detail on how this works by wallet and at brokers.^[2] Either way, the choice depends on records you kept at the time. Ask a tax pro which method applies to your sales.

What good records look like

For every lot, the IRS lists what you need: the asset, date and time, number of units, fair market value in dollars, and basis.^[2] In practice that means one row per purchase or receipt, with the fee, the wallet it sits in now, and a transaction ID you can point to.

That's what the free checklist below builds. It walks you through every wallet you've ever used, one row per lot, and the events people forget: swaps, spending, rewards, self-transfers and broker forms. It ends with a three-question year-end test.

What it doesn't do is tell you what to do with those records next. Choosing a custody setup, planning a move to cash, and leaving a usable note for your family are a bigger job. A deeper guide on custody is coming.

Sources

1. IRS, Frequently asked questions on virtual currency transactions (Q7 gain or loss, Q8 basis includes fees, Q16 to Q18 exchanges, Q38 transfers between your own wallets, Q39 to Q41 specific identification and FIFO). The IRS notes these FAQs generally apply to transactions before January 1, 2025: irs.gov
2. IRS, Digital assets (property treatment, the tax return question, fees paid in digital assets, staking and mining income, records, Form 1099-DA phase-in, Rev. Proc. 2024-28): irs.gov
3. IRS, Understanding your Form 1099-DA: irs.gov
4. IRS, Revenue Procedure 2024-28, allocating basis to wallets and accounts as of January 1, 2025: irs.gov

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This article is educational and informational only. It is not financial, tax, or legal advice, and it is not tailored to your situation. The tax notes are general US notes only, based on IRS guidance. Ask a tax pro how they apply to you. Rules and figures described are current as of October 2026 and can change.

Rules in Brazil and the US change. Check current rules with a qualified professional in Brazil and a US tax pro before acting.

TAD, The Alt Desk. Brazil. Tangibles. Rails.