What is the NGX All-Share Index and how does it track the Nigerian market?

The NGX All-Share Index is the most watched gauge of the Nigerian equity market. Investors, researchers, and the press quote it daily, but few know exactly how it is built and where it falls short.

1. The NGX All-Share Index (NGX ASI) is a market capitalisation weighted index that includes every listed ordinary share on the Nigerian Exchange.
2. It is calculated using a base value of 100 points from 1984, and changes daily based on price movements and adjustments for corporate actions.
3. The index is a price return index. It does not include dividends, so investors who tap into the 10% withholding tax system on Nigerian dividends experience a different total return.
4. Because some NGX stocks trade thinly, the index can be swayed by a handful of liquid large caps, and many shares in the index are hard to trade in size.
5. For a full picture of the Nigerian market, combine the index with total return estimates, dividend records, and scrutiny of the weights and liquidity of the largest components.

What the NGX All-Share Index measures

The index aims to represent the broad Nigerian equity market. It covers the price performance of all listed companies, from banks to consumer goods and industrials. When investors say "the Nigerian market is up", they are usually referring to the NGX ASI.

The index is a price return index, so it only reflects changes in share prices. It does not include dividends, which are a major source of income on the NGX. This distinction becomes central when you compare index performance to what an actual investor receives from a portfolio of Nigerian stocks.

How the index is calculated

Market capitalisation is calculated as price multiplied by total shares outstanding for every listed equity. The market values are summed and compared against a base period, originally set at 100 in 1984. Corporate actions such as bonus issues and rights issues are adjusted so that the index only reflects genuine price changes, not changes caused by the share count.

The NGX ASI is a total market capitalisation index, not a free-float index. That means the entire issued share capital of each company is included, even if a large percentage is not available for trading. In practice, this can overweight companies with substantial cross shareholdings or government stakes.

What the index does not capture

• Dividends are not included. The NGX ASI only captures capital gains, so when dividends are paid, the index does not reflect that income.
• The 10% withholding tax on dividends is also invisible to the index. For Nigerian residents, this tax is often the final tax on dividend income, so net returns are lower than the index's headline move.
• Thin liquidity in many small and mid caps means the index's aggregate value may not be achievable at once. A few liquid large caps can dominate daily moves.
• The index does not represent the broader Nigerian economy. Many growing sectors, especially private companies and unlisted businesses, are simply not part of it.

Why Nigerian specifics matter

Banks form a large part of the NGX ASI, and they report under IFRS. IFRS accounting introduces fair value adjustments and one-off items that can make reported earnings volatile. But the index only records price movement, so it does not directly reflect these fundamental changes.

Investors hold shares through CSCS accounts, and their statements show actual entitlements and tax deductions. The index, however, is a theoretical aggregate. A typical investor's return will differ because of dividends, withholding tax, brokerage costs, and the fact that they cannot trade all index constituents at their quoted prices.

Thin liquidity also matters. Many NGX stocks trade only occasionally, so their last price may be stale. This can make the index's value look steadier than the market actually is. When large trades do occur, they can create outsized moves in individual components and the index itself.

The bottom line

The NGX All-Share Index is a useful daily pulse of Nigerian listed equities, but it is not the whole story. Investors should pair it with dividend tax calculations under Nigeria's 10% withholding tax, a review of the most heavily weighted stocks, and a clear awareness that the actual tradeable experience of the market depends on liquidity and corporate actions.

None of this is personalised financial advice. It is analysis and education for the Nigerian market.

AlphaTeak scores any stock across eight pillars, estimates fair value, and keeps an honest, public track record. Analysis and education, not advice.

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