Education

Before Buying a Stock, Check Sector Concentration in Your Portfolio

By Walid Mograbi · 2026-04-11 · 2 min read

A portfolio can look diversified by number of positions while still depending on a single sector driver.

Why this lesson matters

A portfolio can look diversified by number of positions while still depending on a single sector driver.

The core idea

Counting stock names is not enough, because several positions can still move with the same sector story.
Review sector weight and sector drivers to see whether the portfolio is truly diversified.
A broader fund or a wider mix can reduce sector concentration when you do not want one theme to decide the whole outcome.

Practical example

An investor owns several technology stocks and discovers that the portfolio is still one sector bet, so the next allocation goes into a broader mix instead of another similar name.

Common mistakes to avoid

Counting positions instead of measuring sector exposure.
Assuming different company names mean different risk drivers.
Ignoring broader-fund options when sector exposure is already high.

What to do next

This reveals risk that does not appear from the number of positions alone and gives a more honest measure of diversification.

Important caution

Having many holdings does not mean real diversification if the sector driver is the same.