Do you have to? I'll be 45 in a few days, but even at that age, I'm still not expecting to need anything I have invested for at least 20 years, the ratio of the value of the broad overall market then to now is still likely to be a larger multiple than for any other asset class I can expose myself to. If there's really a bubble, maybe that won't be true in 5 years, but I've yet to see a downturn that didn't recover in 20. Even if your predictions are directionally correct eventually, if you're not clairvoyant, trying to time the market is still not a great idea.