People keep talking about how crazy the market is, up more than 25% this year. It's a big year to be sure. But on the the other hand, even though the market has been decent in recent years, it hasn't been particularly bubblicious.
To put the 25% return into context, I think it's a good idea to look at it over 2 years or 3 years. Since the end of 2017, for example, the market has return an annualized 8.4%/year. Pretty good to be sure. Since the end of 2016, its up around 12%/year. Going back five years, it's up 8.8%/year (these figures exclude dividends).
Not bad at all, but not bubble-like either. If you were going to train an AI machine to look for bubbles, you would look at valuations (interest rate adjusted), sentiment etc. But one of the biggest factors that I would include would be historical returns over various time frames; strong performance reinforces the positive loop of increasing positive sentiment -> higher prices -> better-looking historical returns -> increasing optimism and 'proof' (both statistical and social) of the greatness of stocks etc.
The 10-year return is 10.9%/year, but that's off a depressed level due to the great recession. Over 20 years, the market has gone up only 4%/year.
Here is a table of the S&P 500 index change over various time periods.
S&P 500 Annualized Returns Through November 2019 (excl. dvd)
1-year return: 25.30%
2-year return: 8.39%
3-year return: 11.95%
4-year return: 11.34%
5-year return: 8.81%
10-year return: 10.91%
20-year return: 3.87%
30-year return: 7.55%
50-year return: 7.31%
S&P 500 Annualized Returns Through December 1999 (excl dvd)
1-year return: 19.53%
2-year return: 23.05%
3-year return: 25.64%
4-year return: 24.28%
5-year return: 26.18%
10-year return: 15.31%
20-year return: 13.95%
30-year return: 9.67%
50-year return: 9.36%
This is pretty insane. The annualized return over 5 years to December 1999 was 26%! And we are sort of freaking out that the market is up over 25% year-to-date in a single year, and not even double digits annualized over 2 years.
So anyway, that's why it doesn't really feel like a bubble. People aren't quitting their jobs (to trade stocks), buying new cars (with their capital gains), bigger houses and things like that we saw back in 2000. Most people I talk to still tend to hate stocks, the financial crisis still fresh in their minds.