FTSE 100 Index

What Is the FTSE 100 Index?

The FTSE 100 Index tracks 100 of the largest eligible companies listed on the London Stock Exchange. It is the most widely cited UK large-cap equity benchmark and is commonly used as shorthand for the performance of the largest UK-listed public companies.

The index is maintained by FTSE Russell as part of the FTSE UK Index Series. Although it is associated with the United Kingdom, many FTSE 100 companies earn significant revenue overseas. That makes the index a large-cap UK-listed benchmark, not a pure measure of the domestic UK economy.

How the FTSE 100 Works

FTSE Russell ranks eligible companies within the UK listed-equity universe and maintains the index through regular reviews. Companies can enter or leave the FTSE 100 as their market value changes or as they meet or fail eligibility requirements. The index is generally market-cap weighted, so larger constituents have more influence on performance.

Because of that weighting, the FTSE 100 can be driven by a small number of large sectors or companies. Energy, financials, consumer staples, pharmaceuticals, mining, and other global industries can affect the index differently from a more domestically focused basket.

How Investors Use It

Investors use the FTSE 100 as a benchmark, an index-fund target, a derivative reference, and a market sentiment gauge. UK equity funds may compare returns to it, and global investors may use FTSE 100 products for exposure to large UK-listed companies.

The index is also watched for income because some large constituents have historically paid dividends. Dividend yield can be attractive, but it should not be read in isolation. Dividend sustainability depends on earnings, cash flow, debt, capital needs, and industry conditions.

FTSE 100 Versus FTSE 250

The FTSE 100 captures the largest UK-listed companies, while the FTSE 250 captures the next tier of mid-cap companies. The FTSE 100 often has more multinational revenue exposure. The FTSE 250 can be more sensitive to UK domestic conditions, though neither index is a perfect economic proxy.

That difference helps explain why the indexes can diverge. Sterling, commodity prices, global growth, UK interest rates, and sector mix can affect the two benchmarks in different ways.

Risks to Watch

A FTSE 100 fund may feel diversified because it owns many companies, but concentration can still appear through sectors, currencies, or a handful of large constituents. Investors should review top holdings, fund fees, tracking method, dividend policy, and how the exposure fits with global holdings.

Large-cap status does not remove risk. The index can decline during recessions, commodity shocks, banking stress, political uncertainty, or global risk-off periods. It is a benchmark, not a capital guarantee.

Currency translation can also matter. A company may report in sterling, earn revenue globally, and be owned through a fund held by an investor using another home currency. The index level is only one part of the realized return for an international investor.

That is why fund structure and currency exposure should be checked before assuming a FTSE 100 product is a simple UK domestic bet.

Investor Takeaway

The FTSE 100 Index is the flagship benchmark for UK-listed large-cap stocks. It is useful for tracking a major segment of the public equity market, but its global revenue mix and sector weights mean investors should look beyond the headline level before drawing conclusions.