How to Reconstruct Missing Crypto Cost Basis (And Why the IRS Assumes Zero)
Missing crypto cost basis means the IRS treats your entire sale as profit. Learn step-by-step methods to reconstruct your records and avoid paying phantom gains.
You sold some crypto. You know you bought it years ago. But when you sit down to do your taxes, you realize you have no record of what you originally paid. The IRS may treat your entire sale as pure profit.
Why the IRS Assumes Your Cost Basis Is Zero
If you cannot prove what you paid for an asset, your cost basis defaults to zero. The burden of proof is on you under IRC Section 1012.
How Cost Basis Goes Missing
- Transfers between exchanges — receiving exchange does not know purchase price
- Exchanges that shut down — Mt. Gox, FTX, Cryptopia
- Early crypto with no paper trail — cash purchases, mining in 2013
- DeFi activity — tokens from pools, farming, bridges
- Airdrops you forgot to record
Step-by-Step Reconstruction Methods
- Check old exchange accounts — many retain history for years
- Search your email — purchase confirmations, trade notifications
- Review bank/credit card statements — match fiat deposits with dates
- Use blockchain explorers — find transaction dates, pair with historical prices
- Reference historical price data — CoinGecko, CoinMarketCap snapshots
- Reasonable estimation — document your methodology carefully
What the IRS Considers "Adequate Records"
Date acquired, date sold, proceeds, and cost basis — applied consistently. A reconstruction file showing your methodology demonstrates good faith effort.
The Specific Identification Advantage
If you can prove which specific coins you sold, you can choose your highest-cost lots first, minimizing taxable gains. See our crypto tax checklist before filing.
How Blockchain Smart Tax Catches Missing Cost Basis Before You File
Our Tax Health page automatically scans every transaction and flags anything with missing, zero, or suspicious cost basis.
- Auto-detects transfers between your own wallets and carries cost basis forward
- Historical price lookups across all 550+ supported chains
- Manual cost basis entry for items that cannot be auto-resolved
- "Mark as Worthless" for dead tokens
Get started for free and see where your cost basis stands — before the IRS does. Check our pricing page for plans that fit your portfolio size.
Handle Cost Basis Reconstruction Automatically
Blockchain Smart Tax automates the hard parts of cost basis reconstruction — connecting to 550+ blockchains, classifying every transaction, enforcing per-wallet cost basis tracking (as required by the IRS), and generating the forms you need to file.
How we compare to other crypto tax platforms:
- Koinly ($49+/year) — established platform with strong exchange integrations and a large user community
- CoinTracker ($59+/year) — polished interface with strong Ethereum and exchange support
- CoinLedger ($49+/year) — competitive pricing with good NFT and exchange support
- Blockchain Smart Tax (from $25/year) — all cost basis methods free on every plan, automatic wallet discovery across 550+ chains, spam filtering, free during beta with 10,000 transactions
Start your free import — 10,000 transactions included during beta →