NSE All Share Index

The NSE All-Share Index (NASI) was introduced in 2008 by the Nairobi Securities Exchange to provide a comprehensive measure of the overall stock market's performance. Unlike smaller indices that track a select group of companies, the NASI comprises all the securities listed on the exchange, serving as the definitive benchmark index for the Kenyan equity market. It is structured as a market capitalization-weighted index and uses an arithmetic mean calculation, which involves dividing the sum of all listed companies' market capitalizations by a base value that was set at 100 in January 2008. Additionally, the index is rebalanced on a quarterly basis and is actively adjusted to account for key corporate actions, such as stock splits.

Because the NASI is weighted by market capitalization, its relationship to the underlying stocks is highly proportional to their overall size and valuation. This means that rather than treating every company equally, the index's momentum is heavily dictated by the exchange's largest blue-chip entities. For example, because Safaricom alone accounts for roughly 34% to 44% of the entire Nairobi Securities Exchange's market capitalization, its individual share price movements will disproportionately pull the entire NASI up or down. Consequently, while the NASI is designed to track the entire market, its daily performance most accurately reflects the corporate health and stock volatility of Kenya's most heavily capitalized firms, particularly those in the telecommunications and banking sectors.