Ask anyone who traded in January 2008. They will tell you the same thing. Everybody knew the market only went up. The Sensex had crossed 21,000. Your neighbour had a demat account, your barber had a tip, and nobody wanted to hear a warning.
Then, ten months later, it had lost more than half its value. Those who bought at the top spent years just getting back to even.
There was a number, back then, that had quietly gone to an extreme. Hardly anyone in India could see it at the time. Today, that same number is easy to check, and on the world's largest market, it’s climbing again. That is worth ten minutes of your evening. Not to sell anything. To know what you are holding.
One number, one honest question
Start with the question every investor is really asking. ‘Am I paying too much?’
The usual answer is the price-to-earnings ratio, the PE. Take the price, divide by last year's profit. It’s simple, and in a normal year, it’s fine.
The problem is that profits swing. In a boom, they look fat, the PE looks small, and shares look cheap right when they are dangerous. In a slump, profits vanish, the PE explodes, and shares look dear when they are cheap. The tool lies loudest when you most need the truth.
An American professor, Robert Shiller, had a fix. Use ten years of profit instead of one. Adjust each year for inflation, so old and new dollars meant the same thing. Then divide the price by that 10-year average.
Ten years hold a full boom and a full bust. The lies cancel out, leaving a cleaner read on whether a market is expensive or cheap. He called it the cyclically adjusted price-to-earnings ratio (CAPE).
Why the big names swear by it
This is no fringe gauge. Shiller is a Nobel Prize winner.
In March 2000, Shiller published Irrational Exuberance, arguing American shares had lost touch with reality. The Nasdaq peaked that same month, then fell more than 80%. The book came out days before the top.
Even Warren Buffett, who distrusts most ratios, judges the market against the economy and warns when prices race ahead of the value underneath. When a whole market gets pricey relative to the profits backing it, future returns tend to shrink. That is CAPE in a nutshell.
Where the needle sits today
The CAPE on America's S&P 500 reads about 42, against a long-run average of 17.8. American shares cost roughly two and a half times their own history.
Only one month has ever been dearer: December 1999, at 44.2, the very top of the dot-com mania. Today's reading is higher than 99% of every month since 1881.
What holds it up is no mystery. American profits tied to artificial intelligence keep beating expectations, and investors keep paying up. So far, the profits keep arriving.
Six warnings in 145 years
Here is the important part. The ratio has stayed above 30 for two months or more on just six occasions in 145 years. This is the sixth. The other five all ended the same way.
The first ran through 1929, before the crash that began the Great Depression. The second built into the dot-com bust, when the S&P 500 lost 49% and the Nasdaq lost 77%. The third came before the sharp fall of late 2018, the fourth just ahead of the pandemic crash of 2020, the fifth into the bear market of 2022.
Five earlier warnings. Five painful falls. The gentlest still cost investors a fifth of their money.
The ratio does not promise a crash. It has simply never been this high without one eventually arriving.
Now the part nobody tells you
A high CAPE says the price is rich. It does not say when the reckoning comes.
Back in December 1996, a central banker borrowed Shiller's own phrase, irrational exuberance, to warn that American markets looked frothy. He was right, and almost four years early. The market climbed another 71% before it cracked. Anyone who sold on that warning missed one of the greatest rallies ever recorded.
So, treat CAPE as a weather forecast, not a fire alarm. It tells you the odds of a storm have risen, not the day.
Now bring it home to India
Here is what almost no Indian investor knows. We have our own CAPE. And our own history with it is more dramatic than America's.
Two researchers, Joshy Jacob of the Indian Institute of Management, Ahmedabad and Rajan Raju of Invespar, built a CAPE series for India and put it online for free, running on the BSE Sensex and the Nifty 500.
Their study found the same pattern Shiller found abroad. When Indian CAPE is high, the returns that follow tend to be lower, and the falls deeper.
In December 2007, at the height of that everybody-knows bull run, India's CAPE hit 48.45.
Read that number again. India in 2007 was dearer than America has ever been, even at the dot-com peak of 44.2. Our bubble was the bigger one. Yet a public India CAPE series like this one only appeared in 2024, so at the time, almost no one could see how stretched things had become.
What came next still haunts anyone who lived through it. The Sensex peaked near 21,207 in January 2008. By October, it had more than halved. By March 2009, the CAPE had collapsed to 17.94, a fall of 63% from the top. India's valuation in 2007 was steeper than anything Wall Street has recorded.
The Harshad Mehta episode of 1992 taught an early version of the lesson: money pulled from the banking system drove share prices to levels the profits could not support, until it unravelled.
2007 was the same lesson in a bigger classroom. Every Indian boom seems to rhyme. Easy money finds a thrilling story, a crowd decides prices only rise, and valuation climbs to a place it cannot hold.
The good news, for once
Now the twist, and it favours us.
India's CAPE read 29.22 in July 2026, against a long-run average on this series of around 25. So, we sit modestly above our own history.
Dear, yes. Extreme, no.
We are a world away from the 2007 madness.
Better still is the direction. This number peaked at 37.21 in September 2024 and has fallen about a fifth since. Indian shares have already been through a quiet valuation squeeze over almost two years. Prices moved sideways. Profits caught up. That is the healthy way for the froth to leave a market.
One market has already cooled. The other has not.
The plain PE agrees. The Nifty 50 traded at 20.36 on 19 August 2026, below its ten-year average of about 23.4. The large-cap index is not the problem.
So where is the danger hiding?
Not in the large-caps but in the small-caps.
The Nifty Smallcap 250 traded at a PE of 33.6 on 20 August 2026, around 20% above its own five-year median. The Nifty 50 sits below its average; small-caps sit well above theirs.
In June, small-caps carried a premium of roughly 71% over large-caps on trailing profits. History says such gaps tend to close, usually with the small-caps giving way.
So, the risk in an Indian portfolio today is not the headline index. It’s the tail, the small, story-driven stocks bought on hope rather than profit. That is also the easiest part of a portfolio to check tonight.
What checking this ratio actually gives you
Not a tip. Not a target. Something quieter and more useful.
It gives you a way to ask whether you are paying for a business or for a mood, whether the price tracks earnings or floats on a story.
You can’t control when a market turns. You can control what you own when it does.
So, you can take two facts out of this. America's dial is at a 145-year extreme; ours is not, and that gap favours the patient Indian investor.
But one wire still connects the two markets. When Wall Street cracked in 2008, India fell harder, not softer. Foreign money flees the riskier market first, and we are the riskier market.
None of this is a signal to sell. Shiller never treated it as one. A high CAPE simply buys thinner future returns and a bumpier road to collect them.
The warning bell is ringing on someone else's street. We can hear it clearly from here.
That, in itself, is an edge.
Disclaimer: This article is for information purposes only. It is not a stock recommendation and should not be treated as such.
This article is syndicated from Equitymaster.com