fidelity网页上有解释这问题 https://scs.fidelity.com/webxpress/help/topics/learn_account_cost_basis.shtml What cost basis methods are approved by the IRS? The cost basis methods approved by the IRS include: 1） Average Cost Using the average cost, cost basis is calculated based on the average price paid for all shares held, regardless of holding period. Gains or losses are defined as short-term or long-term based on the assumption that the oldest shares are sold first, even though the average cost is the same for all shares. This method of calculating cost basis is permitted for mutual funds only and cannot be used to calculate cost basis for individual securities such as stocks and bonds. Fidelity uses the average cost method when calculating your cost basis for all mutual fund shares. 2）First In, First Out (FIFO) Using FIFO, cost basis is calculated using the specific amount paid for shares. This method assumes that the first shares you sell are the first you bought. Fidelity uses FIFO when calculating your cost basis for individual securities, such as stocks and bonds. 3）Specific Shares Using specific shares, cost basis is determined by you, the shareholder, when you sell the shares. This method lets you identify which shares you are selling, giving you the most control over the amount of realized gains and losses. The IRS requires you to identify specific shares to Fidelity at the time you sell them. You may identify specific shares for sales of individual securities when you submit the trade. You are not permitted to make the determination after the fact.
真的是这样那就太坑了！ 因为会不断买入
你可以选择卖哪一笔的 在你的股票账户里操作
What cost basis methods are approved by the IRS? The cost basis methods approved by the IRS include:
1） Average Cost Using the average cost, cost basis is calculated based on the average price paid for all shares held, regardless of holding period. Gains or losses are defined as short-term or long-term based on the assumption that the oldest shares are sold first, even though the average cost is the same for all shares. This method of calculating cost basis is permitted for mutual funds only and cannot be used to calculate cost basis for individual securities such as stocks and bonds. Fidelity uses the average cost method when calculating your cost basis for all mutual fund shares.
2）First In, First Out (FIFO) Using FIFO, cost basis is calculated using the specific amount paid for shares. This method assumes that the first shares you sell are the first you bought. Fidelity uses FIFO when calculating your cost basis for individual securities, such as stocks and bonds.
3）Specific Shares Using specific shares, cost basis is determined by you, the shareholder, when you sell the shares. This method lets you identify which shares you are selling, giving you the most control over the amount of realized gains and losses. The IRS requires you to identify specific shares to Fidelity at the time you sell them. You may identify specific shares for sales of individual securities when you submit the trade. You are not permitted to make the determination after the fact.