Re:Half of US stock fund assets are now invested in index funds
by OscarCunningham on Tuesday May 28, 2019 @04:47AM
(#20028335)
Let's try an example. Suppose company A has 1000000 shares in total, each with market value of $100. Then its market cap is $100 million. Suppose company B has 2000000 shares total, each with market value of $150. Then its market cap is $300 million.
Index funds own shares in proportion to the market cap. So an index fund will own shares of B worth three times as much as their shares in A. Lets say we're looking at a fund that owns $6 million of B and $2 million of A.
Now suppose A's share price doubles to $200 and B's share price falls to $125. Then the value of the index funds shares will now be $2 million × ($200/$100) = $4 million of A, and $6 million × ($125/$150) = $5 million of B. Meanwhile A's market cap has changed to 1000000 × $200 = $200 million, and B's market cap has changed to 2000000 × $125 = $250 million.
Then B's market cap is 1.25 of A's market cap, so the index fund wants to be holding shares in B worth 1.25 the value of its shares in A. It currently has $4 million of A, so it wants to be holding 1.25 × $4 million = $5 million of B, which in fact is the amount that it is already holding.
Index funds own shares in proportion to the market cap. So an index fund will own shares of B worth three times as much as their shares in A. Lets say we're looking at a fund that owns $6 million of B and $2 million of A.
Now suppose A's share price doubles to $200 and B's share price falls to $125. Then the value of the index funds shares will now be $2 million × ($200/$100) = $4 million of A, and $6 million × ($125/$150) = $5 million of B. Meanwhile A's market cap has changed to 1000000 × $200 = $200 million, and B's market cap has changed to 2000000 × $125 = $250 million.
Then B's market cap is 1.25 of A's market cap, so the index fund wants to be holding shares in B worth 1.25 the value of its shares in A. It currently has $4 million of A, so it wants to be holding 1.25 × $4 million = $5 million of B, which in fact is the amount that it is already holding.