AI ref when will the buying start5 Sep 2025 11:35
Great question — this comes up often with ASX200 (and other major equity indices) rebalances.
Here’s how it usually works:
• Announcement date: S&P Dow Jones Indices (the index administrator) announces the changes (adds/deletes) about 2 weeks before they take effect.
• Effective date: The change is implemented at the market close on the rebalance day (usually a Friday). The index opens the following Monday with the new constituents.
For index-tracking funds and ETFs (like ASX200 ETFs, index funds, or futures-hedged portfolios):
• They typically need to match the index exactly at the close of the rebalance day.
• That means the bulk of the forced buying/selling happens into the closing auction on the effective day (Friday close).
• Some active managers and hedge funds trade earlier (after announcement but before rebalance) to position ahead of the flows — this is often called index arbitrage or anticipatory trading.
So in practice:
• Passive funds that must replicate the ASX200 will buy at or just before the official inclusion, usually in the closing match on rebalance day.
• Speculative/active traders may start buying as soon as the announcement is out, anticipating those passive flows.
👉 That’s why you often see the stock being added to the index start rising after the announcement, with an extra liquidity/volume spike on the actual rebalance close.
Would you like me to show you historical examples of ASX200 inclusions (e.g., how the stock price behaved between announcement and effective date)?
Friday 19th closing auction for most of the buying. So hopefully a steady daily rise for 2 weeks and then a 10% day.
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