A rate of tax above which it is unprofitable to engage in a transaction. After the tax is paid, there would not be enough profit or financial benefit for the parties involved to justify the time and effort required to transact business. The break even tax rate in and of itself is essentially a conceptual threshold; a rate below this rate would give investors or other parties incentive to engage in a transaction, whereas a rate above this will not. This rate is not a set numerical rate, such as the Social Security tax rate.

An example of a break even tax rate is illustrated in the following example:

Investor A owns 1,000 shares of stock in ABC Company, and the price is starting to decline. He originally paid $25 per share for the entire lot, and the stock is now trading at about $100 per share.

However, a major financial crisis has hit the company, and the share price is starting to fall rapidly. The investor has held the shares for nearly a year, which means that he can either sell them now and pay tax on his gain as ordinary income, or wait for the one-year holding period date and then sell and pay tax at the lower capital gains rate.

But of course, paying a higher rate on stock sold at $75 per share is probably better than waiting for the stock to fall to $50 per share and then paying a lower rate on less gain.

Of course, the movement of the stock price will ultimately determine which path is better, but there will be a stock price at which the investor will come out the same either way, regardless of whether he reports a short or long-term gain.