Grant Bishop

Tuesday, 10 November 2026 · Markets closed · Edition 20

Join (free)
Menu
Toolkit · Draft, not published

How much of my account rides on its largest few holdings?

Add up the shares of the largest few holdings; that sum is how much of the account moves when they do.

Concentration is a plain sum. List the holdings from largest to smallest by value, take each one’s share of the account, and add the first few. The total says how much of the account rides on those names.

It matters because of the position math in the first lesson. Each holding’s move reaches the account in proportion to its share, so when the largest few holdings move together, the account moves by their combined share times that move.

Worked example

An account of $80,000 holds eight positions. The largest three are worth $20,000, $12,000 and $8,000: shares of 25, 15 and 10 percent. Together the three are 50 percent of the account.

If those three fall 20 percent on the same day and the other five stand still, the account falls 50 percent times 20 percent: 10 percent, or $8,000. The other five holdings, between them the other half of the account, did not move the total at all that day.

Combined share of the account —
Account’s move from them —

The math: the shares added, then times the move, with everything else unchanged. Nothing you enter is stored or sent. This is arithmetic, not a recommendation.

Funds and indexes

A fund is concentrated in the same way, one level down. A broad stock index weighted by company size gives its largest companies the largest shares, and a fund that tracks it holds them in those shares. The provider of each index publishes its largest constituents and their weights on its own pages, usually monthly; the sum of the top ten weights is the index’s top-ten concentration on that date.

To carry that through to an account, multiply: if an index fund is 40 percent of the account and the index’s top ten names are a given share of the index, those ten names are 40 percent times that share of the account, before counting any of the same companies held directly.

What the sum does not say

Combined share describes exposure. It does not say whether the largest holdings will move together, or how often they have; the lesson on correlation will take that up. And it says nothing about what share is right for anyone: it is a measurement, to be read alongside the position math.