Knowledge guide
German tax knowledge

What is cost basis — and why must it not be zero?

Last reviewed: August 15, 2026
Cost basis is what the sold lot cost you: purchase price plus incidental acquisition costs, or market value for a swap, reward or airdrop. If that value is missing, many tools assume zero. Then the entire sale proceeds become the gain. That is the most common reason for a tax bill that is far too high — not the tax rate.
The facts in brief
Cost basis 0The lot’s purchase price is unknown
EffectThe entire proceeds become the gain
ProofA contemporaneous market price, CSV or trade

When is cost basis unknown?

Very old exchange exports without a price column, delisted tokens, ICO buys before public prices, deposits instead of purchases, airdrops without an inflow value. Even large coins can sit without a price in gap years.

What will the tax office accept as evidence?

Exchange CSVs, wallet history, contemporaneous market prices, documented ICO payments. A later estimate needs a source and a date. “About today’s price” is not enough. Prefer an archived chart or a nearby trade from the same wallet.

How does chain.report fix missing prices?

CleanUp lists every movement without a price, with coin, date and wallet. Known pairs can be reloaded; exotic ones you enter once. The report is generated only after open price gaps are closed or deliberately documented.

Sources

Section 23 EStG — private disposals

Frequently asked questions

Is cost basis zero the same as a tax-free inflow?

No. Cost basis zero means the tool does not know a value. A genuinely unpaid event must be classified as such, not as a purchase without a price.

Can I ignore missing prices if the amount is small?

Small gaps add up. A single old lot without cost basis can turn an entire sale into gain.

Does the fee belong in the cost basis?

Incidental acquisition fees generally increase cost basis. Selling fees reduce proceeds. Deducting them twice understates the gain.

Read next

Why does CoinTracking set cost basis to zero?

Cost basis zero in CoinTracking comes from missing purchases or prices. How you stop the phantom gain in the tax report.

Why is my crypto tax bill unrealistically high?

An unrealistically high crypto tax bill almost never comes from the tax rate. Usually cost basis, purchases or classification are wrong.

FIFO or LIFO: which method applies to crypto in Germany?

FIFO is the usual German method for private crypto disposals. What LIFO and average cost change — and why missing buys break every method.

This guide structures the data issues and common German administrative practice. It is not tax advice. The assessment in your case stays with you and your tax advisor.

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