How much does not timing the market affect you? Look at this chart (Info from Fidelity Investments). It shows the effects of missing the 10 best days of the market can have on your portfolio - cut your portfolio value into half. Well, such a great timer who can call all the best days correctly will obviously be a God in Investing, but it is impossible! Moreover, this portfolio does not seem to show the effect of calling just 10 days incorrectly for your investing career! A simpler way is obviously to look at the value of the companies you invest in and see if the price makes sense on the long term perspective? If it does, go ahead. If it doesn't, chuck it! Or, one can simply do dollar cost averaging all the way through for at least 10 years. That can obviously give you a good advantage in terms of cost while spending least amount of time. The time would have been spent on just initially choosing a stock that can survive the competition for 10 long years (in today's world!). As this guy de Aenlle says, such studies are not rooted in realities on ground: "The problem with this study, and others like it, is that they have little grounding in real-world investing," he wrote. "For example, as far as we know, no one with both feet on the ground has ever put together a market timing system without considering how it would have done in the past. Obviously, every system is going to miss some up moves, but you would have to be an incredibly perverse genius to miss every good month in 62 years." Read more