Definition
Corporate Action
A change to a constituent's share structure or listing status — a merger, spin-off, split, delisting or acquisition — that requires the index to adjust outside the normal rebalance cycle.
- Status
- Definition in force
- Method version
- 1.0
- Reviewed
- 2026-08-22
In the Live Index framework
Corporate actions are the one category of intra-cycle change a rules-based index cannot defer. A delisted company cannot remain in an index at a stale price, and a two-for-one split that is not adjusted for produces an artificial halving of the level.
The framework specifies the treatment in advance for each action type: splits and stock dividends adjust the share count with no change to weight; spin-offs are assessed against the eligibility test on their first trading day and admitted only if they pass; mergers remove the acquired listing at the last traded price and redistribute its weight pro rata; delistings do the same. No action is treated discretionarily.
Every corporate-action adjustment is logged with its effective date and the document that evidenced it, so a reader reconstructing the series can see exactly where and why a discontinuity was handled.