What Is the FTSE 100 and How Should You Read Its Movements?

You check the FTSE 100 and see that it is “up 80 points.” Is that a strong day for British stocks, a sign that the U.K. economy is improving, or simply a move driven by a handful of large companies? Those are different questions. The most useful way to read the headline is to check the percentage change, the period being measured, and which companies are driving it before drawing conclusions.

What is the FTSE 100?

The FTSE 100 is a benchmark index of 100 major companies listed on the London Stock Exchange that meet eligibility and investability requirements. It is maintained by FTSE Russell, part of London Stock Exchange Group (LSEG), and commonly appears under the index symbol UKX. Launched in January 1984, it is a widely followed barometer of U.K.-listed large-cap shares, not a direct measurement of the country's gross domestic product, wages, or cost of living.

FTSE Russell ranks eligible companies by their full market capitalization when determining membership, subject to the index rules. Full market capitalization is broadly the share price multiplied by shares outstanding. The index then weights constituents using investable, or free-float-adjusted, market values. As a result, a large company generally has much more influence on the index than a smaller constituent. The official FTSE 100 overview explains the selection and review process.

The FTSE 100 is not a list of the 100 companies with the highest share prices, and it is not equally weighted. Its constituent firms can conduct substantial business outside the United Kingdom. Consequently, movements can reflect global business conditions as much as domestic events.

Step 1: Read the percentage change, not just the points

The index's quoted level is expressed in index points, not pounds or dollars. A movement of 80 points means little without the starting level. The percentage change gives a better sense of the move's size:

Percentage change = (current index level − reference index level) ÷ reference index level × 100.

Illustrative example, not a real market quote: If the FTSE 100 rises from 10,000 to 10,100, it has gained 100 points, or 1%. A 100-point rise from 8,000 to 8,100 would instead be 1.25%. When comparing days or different indices, percentages are usually more informative than raw point changes.

Also establish the comparison period. “Up today” normally compares the current level with the previous trading day's close. “Up this year” generally compares with the preceding year-end level. A one-day rebound does not by itself reverse a month-long decline.

Step 2: Check the timestamp and whether the session is open

The London Stock Exchange's regular main-market trading hours are 8:00 a.m. to 4:30 p.m. London time on normal trading days, subject to holiday arrangements. On November 2, 2026, London uses Greenwich Mean Time (GMT, UTC+00:00), so the regular session corresponds to 08:00–16:30 UTC. During British Summer Time (BST, UTC+01:00), the equivalent UTC window is 07:00–15:30 UTC. The U.K. returned from BST to GMT on October 25, 2026.

Not every on-screen quote is live. The London Stock Exchange's FTSE 100 index page labels its displayed data as delayed by at least 15 minutes. Check the source, timestamp, previous close, and whether you are viewing an intraday reading or an official closing value. The exchange's trading-hours FAQ and the U.K. government's clock-change calendar help resolve timing questions.

Step 3: Find out what is moving the index

The FTSE 100 can move for several reasons at the same time. Broad investor optimism or concern can lift or lower stocks together. Bank of England interest-rate expectations can affect financing costs and valuations. Energy and mining shares may respond to oil and metals prices, while other businesses react to earnings, regulation, or company-specific news. The British pound also matters because international revenues and profits are often translated into sterling.

A weaker pound can make foreign-currency earnings worth more when expressed in pounds, potentially helping some globally active companies. But that is not a guaranteed rule: imported costs, hedging, debt, sector exposure, and investor expectations can offset the effect. A rising index therefore does not automatically mean that sterling has strengthened, that every constituent is up, or that domestic consumers are better off.

Pay attention to concentration. In a simplified example, if a company accounts for 6% of the index and its shares rise 3% while everything else stays unchanged, its contribution is roughly 0.18 percentage points to the index's return. That is an illustration of weighting, not an estimate of any actual company's contribution. It helps explain why the FTSE 100 can rise even when more constituent stocks fall than rise.

Step 4: Separate price performance from total return

The familiar headline FTSE 100 level generally refers to a price-return index. It tracks constituent share prices, with adjustments required by the index methodology, but it does not represent the cumulative return of an investor who receives and reinvests dividends. The FTSE 100 Total Return Index combines price performance with dividends assumed reinvested on the ex-dividend date; a separate net-of-tax version accounts for specified dividend tax adjustments. FTSE Russell describes these distinctions in its FTSE UK Index Series overview.

This distinction matters especially over longer periods. When assessing how a stock fund performed, compare it with an appropriate total-return benchmark in the same currency, not only a price-only headline chart. A fund's actual results also depend on fees, cash holdings, tracking differences, taxes, and the investor's currency.

Step 5: Choose the right comparison index

These benchmarks answer different questions. A strong FTSE 100 alongside a weak FTSE 250 may point toward a divergence between larger internationally exposed firms and mid-sized businesses, but it does not prove a single economic cause. Compare sector composition, currency exposure, and the observation period before interpreting the gap.

Step 6: Understand why the list of companies changes

The FTSE 100 is maintained rather than frozen. Its membership is reviewed quarterly, typically in March, June, September, and December, while corporate actions and some other events can require changes between reviews. A company joining or leaving the benchmark does not automatically make it a good or bad investment; the change may follow size, eligibility, or index-maintenance rules.

Methodology also evolves. In an announcement dated March 26, 2026, FTSE Russell stated that from the June 2026 index review, the minimum free-float threshold for both U.K.-incorporated and non-U.K.-incorporated companies in the FTSE UK Index Series would be 10%, subject to the other eligibility criteria. This is one reason to use current official methodology announcements rather than assuming the rules never change.

Common misreadings to avoid

• “The FTSE 100 rose, so the entire U.K. economy is doing well.” It measures a particular group of listed shares, not the whole economy.
• “A 100-point gain is always the same-sized move.” Its percentage size depends on the starting level.
• “Every stock must be rising.” Larger weighted constituents can dominate the index's move.
• “The index gained 5%, so investors earned exactly 5%.” Dividends, fund expenses, taxes, entry points, and currency conversions can change realized returns.
• “The quote on my screen is happening right now.” Displayed index data may be delayed, and the market may be closed.

A quick self-check before interpreting the next FTSE 100 headline

1. Confirm the number: note the index level, point change, percentage change, and reference period.
2. Confirm the clock: note the quote's timestamp, time zone, trading status, and whether it is delayed.
3. Identify the drivers: look at the largest constituent contributions, sector performance, major company announcements, commodity prices, and sterling.
4. Choose an appropriate benchmark: use price return for a headline market move and total return for longer-term investment performance, with consistent currency and dates.
5. Test your conclusion: ask whether the evidence supports a claim about large-cap stocks only, or whether broader U.K. data would be necessary.

Bottom line: The FTSE 100 is a useful snapshot of major London-listed shares. Read its movements as changes in a weighted stock-market benchmark, not as a complete verdict on the British economy or your personal investment returns. If you can explain the percentage move, time window, dominant contributors, and return measure, you are reading the headline on much firmer ground.