什么是虚卖（wash sale）？虚卖是指个人，个人的配偶或个人控制的公司亏本出售了证券，并在此次出售之前或之后的 30 天内，购买相同或基本相同的股票或证券。之所以有这么一说，是因为资本投资的亏损在美国税务上是可以作为抵税的项目扣除的。为了防止投资者故意在投资亏损时卖出造成可抵税投资亏损再买入保持仓位而设置的。一旦61天的期限结束，洗售规则将不适用于相同或相似证券的交易。

不过，虽然触发了虚卖的资本损失无法抵税，但会被加入再次购买的证券成本中去，之后再次售出的时候便可以计入损失。因此损失并不是消失了，只是被延迟了。

为了帮助大家理解，举个简单的例子。我在时间a, 以每股200美金的价格购买了100股苹果. 到了时间b，苹果股价降为150美金，我卖出所有股份，并在一周后以每股170美元的价格再次买入100股。那我第二次购买就实现了虚卖，因为距离上次卖出只有一周时间。因此我的第一次卖出损失100×（200-150）=5000美金，就被计入了后一次购买的成本，成本是170×100+5000=22000。后一次购买的成本变成了220每股。

我第一次进行虚卖操作的时候，以为不小心违法了。我当时并不是为了实现资本损失抵税。纯粹是因为资金不够，短期只能通过卖出亏损的股票期待在股价下跌更多的时候以更低的成本再次买入。结果收到交易商的通知，说我有虚卖的操作。虚卖本身是没问题的，想要降低持仓成本的各位大可以高买低卖更低买。但操作本身涉及择时，要是不小心落得高买低卖再高买的境地就不划算了。

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What is wash sale? Wash sale occurs when an individual, individual’s spouse or individual owned company sells a security at a loss and, within 30 days before or after this sale, buys the same or an identical security back, or does so through a contract or option. Because capital loss is tax deductible, wash sale rule is to prevent a taxpayer from taking a tax deduction for a loss on a sold yet immediately bought back security. Once the 61-day rule expires, wash sale rule does not apply anymore.

However, even though loss in a wash sale is not tax deductible, it will be added to the cost of the repurchased security. When those get sold, the capitol loss is eventually realized. Therefore, the capitol loss does not disappear. It is just postponed.

To make it easier to understand, I’ll give an example. I bought 100 shares of apple stocks at $200 per share at time point a. At time point b, apple stocks price went down to $150 per share, and I sold all my 100 shares. I ended up with a 100*($200-$150)=$5000 loss. Just after a week, I bought back 100 apple shares at $170 per share. This exact purchase violated the wash sale rule because it happened only a week away from my last sale. Therefore, my $5000 loss will not be tax deductible, but it will be added to the cost of my later purchase, which increased my repurchase cost basis to (100*$170+$5000)/100=$220 per share.

The first time I was notified of a wash sale violation, I was so worried I did something illegal. Back then, I was just trying to lower my security cost basis through selling shares and repurchasing them at a even lower price. Selling at a loss and shortly buying back is not problematic at all if you do not claim tax deduction. If you think you could buy the security back at a lower price you can definitely do it. However, the reality usually ends up the opposite – having to repurchase the shares at a even higher price after selling at a loss. After all, it is not wise to time the market.