Is the 'perfect' timing strategy truly perfect?

In the presence of transaction cost, the 'perfect' timing strategy which holds stocks in a period with positive excess return and holds cash in a period with negative excess return is not necessarily perfect. Using the optimal growth criterion, this paper derives the truly perfect timing strategy which can achieve the maximum long term growth. It is found that such a perfect timing strategy can achieve a much higher annual return than the 'perfect' timing strategy under reasonable transaction cost. Also, it can achieve a return of over 80% when a review period is as short as a day and when transaction cost is low. Using the truly perfect timing strategy as a benchmark, the likely gains from imperfect timing can be more accurately assessed. For a less frequent review schedule, a market timer needs a very high correct prediction probability in order to be at par with the buy-and-hold strategy. However, the needed correct prediction probability is much less when the review schedule is more frequent. Also, the correct prediction probability needed to be at par with the buy-and-hold strategy increases with the transaction cost.