The point
Market cap is a company's share price multiplied by its number of shares: 200 crore shares at ₹500 make ₹1,00,000 crore. When that number falls, no money leaves anyone's account. It is a valuation of the whole company at the price of the last trade, and what fell is the price the next buyer will pay.
How is market cap calculated?
Market cap is the number of shares outstanding multiplied by the price of one share. Zerodha's support page gives the same rule with a small case: 5,00,000 shares at ₹500 each make a market cap of ₹25 crore. Scale it up and a company with 200 crore shares at ₹500 is worth ₹1,00,000 crore on the screen.
The price in that sum is the price of the most recent trade. One price is applied to every share, including the ones that did not change hands in that session. That explains most of what confuses people about the number.
Why "erased" is the wrong word
Take that same company. The price falls from ₹500 to ₹450, a 10 percent drop, and the headline says ₹10,000 crore erased. The arithmetic is right: 200 crore shares times ₹50 is ₹10,000 crore.
Now look at what changed hands. Suppose 1,000 shares traded at ₹450 that day. Buyers paid ₹4.5 lakh and sellers received ₹4.5 lakh. Every rupee a buyer spent reached a seller. The remaining shares never moved, yet each is now marked ₹50 lower.
Nothing left a bank account to cause that markdown. The last trade set a new price, and the whole company was re-priced to match it.
For a holder, the loss is real in one sense and unrealised in another. Say three percent of a ₹1 crore portfolio, ₹3 lakh, sits in this stock. At ₹450 the position reads ₹2.7 lakh, a mark-down of ₹30,000. That figure becomes a loss in hand only if the position is sold at that price. It moves back if the price does.
What is free-float market cap?
Free-float market cap counts only the shares that are available to trade on the exchange. Shares held by promoters and other locked-in holders are left out, because they are not offered to buyers on any given day.
Take the same ₹1,00,000 crore company and suppose promoters hold 60 percent. The free-float market cap is 40 percent of it, ₹40,000 crore. The full figure says what the company is worth. The free-float figure says how much of it a buyer could actually purchase.
Indices use the second figure. Angel One's report on the NSE Indices review of the Nifty 50 shows how. A stock is admitted on its six-month average free-float market cap, and it needs at least 1.5 times that of the smallest constituent it replaces. One stock was added to the Nifty 50 effective 30 September 2026 on a six-month average free-float market cap of ₹1,40,879 crore, against ₹55,930 crore for the constituent it replaced. That is 2.5 times, above the 1.5 times bar. Only stocks in the NSE Futures and Options segment are eligible.
What are large, mid and small caps?
India ranks companies by full market cap, and the rank gives the label. Zerodha's page summarises the SEBI framework of 6 October 2017. The top 100 companies are large cap. Those ranked 101 to 250 are mid cap, and those from 251st onward are small cap. AMFI publishes the list.
The label follows the rank, and no rupee cutoff sits behind it. A company keeps its label only as long as its rank holds, and the list is re-cut periodically. A large cap that falls hard can be a mid cap on the next list without a single share being sold by anyone who holds it.
How does a market cap index hold less of a falling stock?
A market cap weighted index sets each member's weight by its share of the total value. Take two stocks, A at ₹60,000 crore and B at ₹40,000 crore. Their weights are 60 percent and 40 percent. If A falls 10 percent, A is worth ₹54,000 crore and B is still worth ₹40,000 crore. The total is ₹94,000 crore. A's weight is 54,000 divided by 94,000, or 57.4 percent.
Nobody sold anything. The weight shrank because the price did. That is how a cap-weighted index trims a falling name automatically, and how it grows the weight of a rising one.
The same logic applies to crypto, where market cap is the number of coins in circulation multiplied by the price of one coin. A price move re-values every coin in circulation at once. What a rule-based index does with such a move is a separate question. Qatobit's QSI indices rebalance monthly on a documented methodology, so the basket resets on a schedule instead of on a headline. The crypto index explainer covers how that works.
What to do with the number
Read market cap as a size and a ranking. Two questions make it useful. Is this the full figure or the free-float figure? And how much of it could a buyer actually trade on a bad day? That is a liquidity question, covered in what liquidity is and what it looks like on a bad day.
The same idea appears in what an FII is and what its selling does to the index. Every seller has a buyer, and the price is where they met.
After a crash the next trade happens at a lower price, and market cap reads lower because it is that price applied to every share. The share count is the same, and every rupee a buyer paid reached a seller.
Frequently asked questions
What is market cap?
Market cap is a company's share price multiplied by the number of its shares outstanding. It is the value the market puts on the whole company at the price of the latest trade.
How is market cap calculated?
Multiply the number of shares outstanding by the price of one share. Zerodha's example is 5,00,000 shares at ₹500 each, which gives a market cap of ₹25 crore.
Does money disappear when the market falls?
No. Every rupee a buyer pays reaches a seller. What falls is the price applied to every share, including shares that did not trade, so the market cap reads lower while no money leaves anyone's account. A loss is realised only when a position is sold.
What is free-float market cap?
It is market cap counting only the shares available to trade, leaving out promoter and other locked-in holdings. If promoters hold 60 percent of a ₹1,00,000 crore company, the free-float market cap is ₹40,000 crore. Indices such as the Nifty 50 use it to decide who enters.
What is market cap in crypto?
It is the number of coins in circulation multiplied by the price of one coin. A price move re-values every coin in circulation at once, and that move alone takes no money out of anyone's account.
Crypto investments are subject to market risk. Not financial advice.
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