The FTSE All-Share Index is a broad UK equity benchmark formed by aggregating the FTSE 100, FTSE 250, and FTSE SmallCap indexes. FTSE Russell states that it represents about 98% to 99% of UK market capitalization under the current methodology. It is broad, but it does not include every security traded on the London Stock Exchange.
The historical name Financial Times-Actuaries All-Share Index may appear in older data, contracts, and research. Current analysis should identify the modern FTSE All-Share series, variant, methodology version, and date rather than assuming every historical label is directly comparable.
Key Takeaways
- FTSE All-Share combines large-, mid-, and small-cap segments of the eligible UK equity market.
- It is broader than the FTSE 100 but remains capitalization weighted, so large companies usually dominate its return.
- Coverage of 98% to 99% refers to eligible UK market capitalization, not to 98% to 99% of all London-listed securities by count.
- Index weights use investability adjustments such as free float; full company value and index weight are not interchangeable.
- Price-return and total-return variants produce different performance figures.
- A broad benchmark can still be concentrated by company, industry, revenue geography, and currency exposure.
- Funds linked to the index can differ from it because of fees, taxes, cash, sampling, and trading.
What the FTSE All-Share Includes
The index is an aggregation of three non-overlapping size segments:
| Component | Segment represented | Relationship to the All-Share |
|---|
| FTSE 100 | Large-cap eligible UK companies | Largest-cap segment and usually the greatest share of index value |
| FTSE 250 | Mid-cap eligible companies outside FTSE 100 | Extends coverage beyond the largest 100 |
| FTSE SmallCap | Smaller eligible companies outside FTSE 350 | Adds small-cap breadth |
The aggregation describes constituent membership and weights. It does not mean analysts can add the three published index levels. Each component has its own divisor and base level, so FTSE 100 level + FTSE 250 level + FTSE SmallCap level has no financial meaning.
How the Index Is Weighted
The All-Share follows the FTSE UK Index Series framework. Eligible securities are assigned index shares and investability weights. A simplified constituent weight is:
$$
w_i = \frac{P_i Q_i F_i}{\sum_{j=1}^{N} P_j Q_j F_j}
$$
where (P_i) is price, (Q_i) is the index share quantity, and (F_i) is the applicable free-float or investability factor. A divisor converts aggregate adjusted market value into an index level and is maintained around qualifying constituent and corporate-action changes.
The simplified formula does not replace the official calculation guide. Treatment of multiple lines, rights issues, takeovers, suspensions, currency, taxes, and timing depends on current rules.
Worked Example: Why Broad Does Not Mean Equal Weighted
Assume an illustrative All-Share has only three segments:
| Segment | Float-adjusted market value | Segment weight | Segment return |
|---|
| Large cap | GBP 850 billion | 85% | 4.0% |
| Mid cap | GBP 120 billion | 12% | 8.0% |
| Small cap | GBP 30 billion | 3% | -2.0% |
| Total | GBP 1,000 billion | 100% | |
Ignoring constituent changes and rounding, the weighted return is:
$$
R = (0.85\times4.0\%)+(0.12\times8.0\%)+(0.03\times-2.0\%)=4.30\%
$$
The mid-cap segment performs best, but its smaller weight limits its contribution. The small-cap decline reduces the total return by only 0.06 percentage points in this simplified example. A broad index can therefore include many smaller companies while remaining driven mainly by its largest constituents.
FTSE All-Share vs. FTSE 100
| Question | FTSE All-Share | FTSE 100 |
|---|
| Market segment | Large, mid, and small cap | Large cap |
| Component relationship | Aggregates FTSE 100, FTSE 250, and FTSE SmallCap | One component of All-Share |
| Breadth | Broader eligible UK market | Narrower headline segment |
| Smaller-company exposure | Includes it | Generally excludes it |
| Typical benchmark use | Broad UK equity mandate | UK large-cap mandate |
| Main limitation | Still dominated by larger float-adjusted values | Omits mid- and small-cap segments |
Neither index is universally better. Benchmark choice should match the portfolio’s eligible universe, size exposure, currency, dividend treatment, and investment constraints.
Price Return and Total Return
A price index reflects constituent price movement under the index methodology. A total-return index also incorporates reinvested distributions. The two answer different questions:
$$
R_{price}=\frac{I_1-I_0}{I_0}
$$
Suppose the price index rises from 4,000 to 4,120:
$$
R_{price}=\frac{4{,}120-4{,}000}{4{,}000}=3.00\%
$$
If the matching official total-return series gains 6.20%, use 6.20% for that total-return comparison. Do not mechanically add a quoted annual dividend yield to 3.00%; ex-dividend dates, reinvestment, constituent changes, and measurement periods matter.
Also check whether the total-return variant is gross or net of modeled tax. An investor’s realized tax and costs can differ from the index assumptions.
Why the FTSE All-Share Matters
The index can serve as:
- a benchmark for broad UK equity portfolios;
- the reference for index funds, exchange-traded products, derivatives, and mandates;
- a starting universe for performance attribution and security selection;
- a broad market series for valuation, yield, breadth, and historical analysis; and
- a comparison point for large-cap, mid-cap, small-cap, active, and factor strategies.
Its broader coverage can make it more appropriate than the FTSE 100 for a portfolio allowed to invest across UK company sizes. It does not make the index a complete measure of household finances, private companies, government output, or the UK economy.
What Can Move the Index?
- Changes in prices of large constituents.
- Sector-specific earnings, regulation, and commodity cycles.
- Sterling movements affecting globally earned revenue and investor returns.
- Interest rates, discount rates, inflation expectations, and risk appetite.
- Dividends in total-return variants.
- Initial public offerings, mergers, deletions, and scheduled reviews.
- Changes in shares outstanding, free float, or foreign ownership restrictions.
The same headline return can arise from very different combinations of company and sector performance. Use contribution and breadth data before calling a move “market-wide.”
Risks and Limitations
- Large-company dominance: small caps add breadth by count but may contribute little weight.
- Concentration: sectors or individual companies can have outsized influence.
- Revenue geography: UK nationality and index membership do not imply exclusively UK revenue.
- Currency effects: GBP index performance can differ from another-currency investor’s return.
- Eligibility exclusions: listed securities outside the rules are not represented.
- Methodology changes: rules and constituent classifications evolve.
- Backward-looking composition: current constituents should not be imposed on historical returns.
- Implementation gap: products add fees, taxes, spreads, sampling, and tracking risk.
- No suitability test: index membership does not assess an investor’s horizon, objectives, or capacity for loss.
How to Evaluate All-Share Data
- Confirm the exact index name, ticker, currency, and data source.
- Identify price, gross total return, or net total return.
- Match constituent, weight, valuation, and return dates.
- Review top-company and sector concentration, not only constituent count.
- Check free-float, liquidity, listing, nationality, and security-type rules.
- Separate index return from the return of a fund or account.
- For historical work, record methodology and segment changes.
- Use the current official factsheet and ground rules for live decisions.
Common Mistakes
- Saying the index contains every company or security listed in London.
- Treating 98% to 99% market-cap coverage as a percentage of listed-company count.
- Adding the levels of FTSE 100, FTSE 250, and FTSE SmallCap.
- Assuming more constituents make the index equal weighted or unconcentrated.
- Comparing the All-Share price index with a dividend-reinvesting portfolio.
- Using a broad UK equity index as a direct measure of UK GDP.
- Ignoring foreign revenue, sterling exposure, investment trusts, and sector weights.
- Treating an index-linked fund as identical to its benchmark.
Authoritative Sources
- LSEG: FTSE UK Index Series defines the All-Share as the aggregation of FTSE 100, FTSE 250, and FTSE SmallCap and provides current coverage, factsheets, constituents, and methodology links.
- FTSE UK Index Series Ground Rules governs eligibility, segment membership, reviews, and maintenance. Check the version and effective date.
- LSEG index policy and methodology provides calculation, free-float, corporate-action, and governance resources.
- LSEG benchmark statements identifies regulated benchmark families and methodology context.
FAQs
Is the FTSE All-Share the whole London Stock Exchange?
No. It covers a broad set of eligible UK equities under FTSE Russell’s rules, but it does not include every security listed or traded in London.
Does the FTSE All-Share include the FTSE 100?
Yes. The FTSE All-Share aggregates the FTSE 100, FTSE 250, and FTSE SmallCap indexes. The component index levels cannot simply be added because each series has its own divisor and base.
Is the FTSE All-Share less risky than the FTSE 100?
Broader company-size coverage can improve diversification, but it does not guarantee lower risk. Concentration, sector mix, smaller-company volatility, currency exposure, valuation, and the holding period still matter.
This article is educational and does not recommend any index fund, security, or investment strategy.