Cost basis

When crypto is sold, swapped or spent, most tax systems measure the gain or loss as the value received minus the cost basis. Basis normally includes the purchase price plus directly related costs such as trading fees. For coins received as income, such as staking rewards, mining income or some airdrops, the basis is usually the market value counted as income when they were received.

Calculating basis gets complicated in crypto because people buy in many small lots, move coins between exchanges and wallets, and swap tokens frequently. When only part of a holding is sold, a method is needed to decide which lots were sold. In the US, taxpayers can use specific identification or default to first in, first out, and since 2025 basis must be tracked per wallet or account. In Spain, the tax agency requires FIFO for homogeneous assets, and the acquisition value includes the costs and taxes inherent to the purchase.

Missing basis records are a common problem, especially for coins bought years ago on exchanges that no longer exist. Without proof, tax authorities may treat the full proceeds as gain.