FTSE UK Index Series

FTSE UK Index Series is a family of stock market indices designed to represent the performance of companies and securities across different capitalisation and industry segments of the United Kingdom equity market. The series is calculated and maintained by FTSE Russell, which is wholly owned by the London Stock Exchange Group (LSEG).

The FTSE UK Index Series includes major UK equity benchmarks such as the FTSE 100, FTSE 250, and FTSE 350, together with other indices covering different segments and investment characteristics.

Purpose

The FTSE UK Index Series provides market participants with a structured set of benchmarks for measuring the performance of the UK equity market.

The indices can be used for:

• investment benchmarking;
• portfolio management;
• passive investment strategies;
• asset allocation;
• investment research;
• risk management;
• creation of exchange-traded funds (ETFs);
• structured investment products;
• index-based derivatives.

FTSE Russell states that its indices are used by institutional and retail investors to benchmark investment performance and create investment products.

Major indices

The FTSE UK Index Series includes several widely followed indices.

FTSE 100

The FTSE 100 comprises the 100 most highly capitalised eligible companies listed on the London Stock Exchange.

It is commonly regarded as a benchmark for large-cap UK-listed equities.

FTSE 250

The FTSE 250 comprises mid-capitalised companies not covered by the FTSE 100.

FTSE Russell states that the FTSE 250 represents approximately 15% of UK market capitalisation.

FTSE 350

The FTSE 350 combines the constituents of the FTSE 100 and FTSE 250.

A simplified relationship is:

$\text{FTSE 350}=\text{FTSE 100}+\text{FTSE 250}$

The FTSE 350 therefore provides broader exposure to large- and mid-capitalisation segments of the UK equity market.

FTSE SmallCap

The FTSE SmallCap provides exposure to smaller eligible UK companies outside the FTSE 350, subject to the applicable index rules.

The broader FTSE UK index structure therefore provides coverage across large-, mid-, and smaller-capitalisation segments.

Index construction

The FTSE UK Index Series uses market capitalisation weighting, with constituent weights based on free-float-adjusted market values.

A simplified representation of an index weight is:

$\text{Index Weight}=\frac{\text{Free-Float-Adjusted Market Capitalisation}}{\text{Total Free-Float-Adjusted Market Capitalisation}}\times 100\mathrm{\%}$

The actual index calculation incorporates the FTSE Russell methodology, including adjustments for free float, corporate actions, share changes, and other relevant factors.

Free-float adjustment

The FTSE UK Index Series uses free-float-adjusted market capitalisation in calculating its indices.

Free float represents the proportion of a company's shares considered available to investors in the public market.

A simplified representation is:

$\text{Free-Float-Adjusted Market Capitalisation}=\text{Market Capitalisation}\times \text{Free Float Factor}$

The methodology contains additional rules governing the treatment of shares and free-float restrictions.

Index calculation

The FTSE UK Index Series uses an arithmetic weighted methodology based on the market capitalisation of its constituents.

A simplified price-index calculation is:

$\text{Index Value}=\frac{\sum _{i=1}^n{\text{Adjusted Market Capitalisation}}_i}{\text{Index Divisor}}$

The divisor is adjusted when necessary to ensure that corporate actions and constituent changes do not create artificial movements in the index.

Index reviews

The FTSE UK Index Series is subject to periodic reviews.

FTSE Russell conducts quarterly reviews in:

• March;
• June;
• September;
• December.

The reviews can result in changes to index constituents, free-float factors, and shares in issue. Corporate actions can also result in changes outside the regular review cycle.

Eligibility

Companies and securities must satisfy the applicable eligibility requirements to be included in the FTSE UK Index Series.

Eligibility can depend on factors including:

• nationality;
• listing;
• security type;
• liquidity;
• free float;
• investability;
• trading characteristics.

FTSE Russell amended certain UK Index Series eligibility rules in 2025, including provisions concerning securities traded in euros or U.S. dollars and fast-entry thresholds.

Fast entry

The FTSE UK Index Series includes mechanisms allowing certain large newly listed companies to enter the FTSE 100 or FTSE 250 outside the normal review process.

Following methodology changes effective from the September 2025 review, an eligible company listing on the London Stock Exchange can qualify for fast entry if it satisfies the applicable ranking and investable-market-capitalisation requirements.

FTSE Russell stated that a company ranking 225th or above on the first day of unconditional dealings and having an investable market capitalisation of at least GBP 1 billion could, if otherwise eligible, enter the FTSE 100 or FTSE 250 after its fifth trading day.

Liquidity requirements

Liquidity is one of the factors considered in the eligibility and maintenance of securities within the FTSE UK Index Series.

FTSE Russell's methodology overview states that liquidity is tested annually in June, while other index maintenance activities occur during the quarterly review cycle.

Corporate actions

Corporate actions can affect the composition and calculation of the FTSE UK indices.

Examples include:

• mergers;
• acquisitions;
• share issues;
• share buybacks;
• stock splits;
• demergers;
• rights issues;
• changes in free float.

FTSE Russell applies adjustments designed to prevent corporate actions from creating artificial discontinuities in index performance.

Price and total-return indices

The FTSE UK Index Series contains different types of index calculations.

A price index measures changes in the prices of its constituents, subject to the applicable index methodology.

A total-return index incorporates both capital performance and income from dividends, with dividends treated according to the relevant FTSE Russell methodology.

A simplified total-return relationship is:

$\text{Total Return}=\text{Capital Return}+\text{Reinvested Dividend Return}$

The exact calculation depends on the specific index variant.

Currency treatment

The FTSE UK Index Series can include securities whose trading currency is not GBP under the applicable eligibility rules.

For index calculations, non-GBP security prices are converted into the index currency using the relevant exchange rates. FTSE Russell's calculation guide specifies the use of real-time exchange rates for intraday calculations and a series-specific exchange rate for end-of-day calculations.

Investment products

FTSE UK indices can serve as the underlying benchmarks for financial products including:

• ETFs;
• index funds;
• structured products;
• futures;
• options;
• other index-based derivatives.

The use of an index as a benchmark does not imply that an investment product will exactly replicate its performance.

2026 review

FTSE Russell conducted the June 2026 annual review of the FTSE UK Index Series.

The review resulted in changes to both the FTSE 100 and FTSE 250. The changes were implemented after the close of business on 19 June 2026 and became effective from the start of trading on 22 June 2026.

Importance

The FTSE UK Index Series provides a comprehensive framework for measuring different segments of the UK equity market. Its major indices, including the FTSE 100, FTSE 250, and FTSE 350, are widely used as benchmarks for investment performance, portfolio construction, asset allocation, risk management, and financial products. Its rules-based methodology and periodic reviews are intended to maintain representative coverage of the underlying UK equity market.

See also

• FTSE 100
• FTSE 250
• FTSE 350
• FTSE SmallCap
• FTSE All-Share Index
• London Stock Exchange
• FTSE Russell
• London Stock Exchange Group
• Stock market index
• Market capitalization
• Free float
• Index fund
• Exchange-traded fund
• Benchmark (finance)
• Portfolio management
• Passive management