The all share market index is a composite measure of the performance of all publicly traded stocks within a specific exchange or region, designed to reflect the health and direction of the equity market. It aggregates price movements across a wide universe of securities, weighted by market capitalization or free float, to provide a single indicator of market-wide trends.
It serves as a benchmark for portfolio managers, institutional investors, and individual traders to evaluate whether their investments are outperforming or underperforming the broader market. Unlike sector-specific indices such as the S&P 500 Energy Sector Index, the all share market index includes nearly every listed company in its coverage area, making it a complete gauge of economic sentiment and investor confidence.
For example, the S&P/ASX 200 Total Return Index-often referred to as the All Share Market Index in Australia-is calculated using all 200 companies in the S&P/ASX 200, adjusted for dividends and rebalanced quarterly. This index rose 12.4% in 2023, reflecting strong gains in financials and energy sectors despite global inflation pressures.
The all share market index uses a weighted average system where larger companies contribute more to the index's movement. This helps a 10% drop in a $500 billion company impacts the index more than a 10% drop in a $5 billion firm. Most indices use free-float market capitalization weighting, which excludes locked-in shares held by governments or insiders.
Index calculation follows a formula: each company's market value is multiplied by its free-float factor (the proportion of shares available for public trading), then summed and divided by a base value set at a historical date. For example, the S&P/ASX 200 was set to 1,000 points on December 31, 1999. As of March 2024, it stood at 8,462 points, indicating a compound growth rate of approximately 3.4% annually since inception.
Rebalancing occurs quarterly to maintain accurate representation. If a company grows rapidly and becomes too large a portion of the index, it may be removed or capped. The FTSE Russell index provider updates eligibility criteria every quarter based on liquidity and market cap thresholds.
Different exchanges publish their own all share market indices. These vary in composition, weighting methodology, and frequency of rebalancing. The following table compares major regional indices:
| Index Name | Exchange | Weighting Method | Base Date | Current Level (March 2024) |
|---|---|---|---|---|
| S&P/ASX 200 Total Return | ASX (Australia) | Free-float market cap | Dec 31, 1999 | 8,462 |
| Nasdaq Composite | Nasdaq (USA) | Market cap weighted | Aug 31, 1971 | 18,743 |
| FTSE 100 Total Return | LSE (UK) | Free-float market cap | Jan 3, 1984 | 8,120 |
The Nasdaq Composite includes all common stocks listed on the Nasdaq exchange-over 3,000 companies-making it broader than the S&P 500, which only includes 500 large-cap firms. This difference affects volatility: the Nasdaq Composite dropped 35% during the 2000 dot-com crash, while the S&P 500 fell 49%, due to higher tech concentration.
A common misconception is that the all share market index represents "the market." But it only reflects the segment of the market that trades on a specific exchange. A company like Tesla, listed on Nasdaq, is included in the Nasdaq Composite but not in the S&P 500 unless it meets size and liquidity criteria.
Many assume the all share market index measures economic growth directly. It does not. While long-term index trends often correlate with GDP growth, they are driven by investor expectations, interest rates, and earnings reports-not macroeconomic data itself. For example, the S&P/ASX 200 rose 18% in 2021 despite Australia's economy contracting by 2.5% in Q1, due to strong commodity prices and low interest rates.
Another error is treating the index as a direct investment vehicle. The index itself is not tradable. Investors access its performance through ETFs like the SPDR S&P/ASX 200 Fund (ticker: STW), which tracks the index and trades on the ASX. In 2023, STW returned 11.8%, closely mirroring the index's 12.4% gain.
There's also confusion between total return and price-only indices. The "Total Return" version includes reinvested dividends. Without this adjustment, returns appear lower. The S&P/ASX 200 Total Return Index gained 12.4% in 2023, while the price-only version rose only 9.2%. The difference stems from dividend income averaging 3.2% annually over the past decade.
An investor managing a $1 million portfolio with 60% equities and 40% bonds can use the all share market index as a benchmark. If the equity portion grows 10% in a year while the index rises 12%, the portfolio underperformed by 2 percentage points. This signals a need to reassess asset allocation or fund selection.
In practice, this benchmarking is automated. Morningstar's Portfolio Manager software automatically compares client portfolios against the S&P/ASX 200 Total Return Index, flagging underperformance and suggesting rebalancing actions. In 2022, 43% of managed accounts showed underperformance relative to the index, prompting adjustments in 28% of cases.
I once reviewed a retirement fund's annual report where the manager claimed "outperformance" because the fund gained 8% while the index rose 6%. But the index was total return, and the fund had excluded dividends. Once corrected, the fund actually underperformed by 1.5 percentage points. This illustrates why understanding index construction matters.
Understanding the all share market index is essential for anyone engaging with financial markets. It provides context for investment decisions, performance evaluation, and risk assessment. Whether tracking the S&P/ASX 200 or the Nasdaq Composite, knowing how it's built and what it represents prevents misinterpretation and supports better outcomes.