This article is educational content explaining how a market mechanism generally works. It is not investment advice and does not describe any specific current event, company, or security.
In Australia, an investor can quietly buy shares in a listed company for as long as they like, until the moment their holding passes one twentieth of the company’s voting shares. At that instant, a legal clock starts running, and the investor has just two business days to tell the market exactly what they hold. Miss that window, and the consequences fall under the Corporations Act itself, not just exchange etiquette. What follows is how this disclosure regime is built, and why regulators designed it around such a specific number.
The 5% Threshold and the Substantial Holder Notice
Under Chapter 6C of the Corporations Act 2001, a person becomes a “substantial holder” in an Australian listed entity once their voting power reaches 5% of the total voting shares on issue. Voting power is not limited to shares held directly: it also captures shares controlled through associates, derivatives, and certain agreements, so the rule is designed to catch economic influence, not just the name on a share register. Once that 5% line is crossed, the holder must lodge a Form 603 (an initial substantial holder notice) with the company and the Australian Securities Exchange, disclosing the size of the holding, the nature of any relevant interests, and the circumstances that gave rise to them, generally within two business days.
This obligation applies whether the holder built the position through ordinary on-market buying, a block trade, a scheme of arrangement, or any other transaction that shifts voting power. The notice becomes part of the public record via the ASX market announcements platform, meaning every other market participant can see who has crossed the threshold and roughly how the position was assembled.
The 1% Rule: Tracking Every Subsequent Move
Reaching 5% is only the entry point. Once an investor is classified as a substantial holder, the Corporations Act requires them to lodge a further notice, this time a Form 604 (change of substantial holding), whenever their voting power moves by 1 percentage point or more in either direction, up or down, from the level last disclosed. A holder who moves from 6% to 7.2%, for example, has crossed a full percentage point and must update the market. So does a holder who sells down from 12% to 10.8%.
The same 1% threshold applies if the holder exits the substantial holding position altogether, dropping back below 5%, in which case a cessation notice is required. Because the trigger is a full percentage point rather than any purchase at all, an investor can trade in smaller increments without lodging a notice after every transaction, but the obligation reactivates as soon as the cumulative change reaches that 1% mark since the last disclosed figure. This creates a rolling, event-driven disclosure ladder rather than a single one-off filing.
Why the Regime Exists and How the Market Uses It
The rationale behind substantial holding disclosure is transparency around control. Ownership concentration can affect a company’s governance, its vulnerability to a takeover, and the balance of power at shareholder meetings, so regulators such as the Australian Securities and Investments Commission treat visibility into who holds meaningful stakes as a core protection for the broader market. Without it, other shareholders and the company’s board could be blindsided by shifts in influence that were assembled gradually and privately.
For company boards, substantial holder notices function as an early warning system, letting them see accumulation patterns before a holder reaches a level where takeover rules or board-composition questions come into play. For other investors and analysts, the lodged notices, all searchable through ASX announcements, provide a documented history of how ownership in a company has evolved over time. This is also why the threshold and increment are calibrated the way they are: 5% is treated as the point where a stake becomes large enough to plausibly influence outcomes, while the 1% follow-up rule ensures the market is not left tracking a stale snapshot indefinitely as that influence grows or recedes.
Understood this way, the requirement is less a bureaucratic hurdle than a structural feature of how Australian equity markets keep ownership information current, ensuring that meaningful shifts in who controls a company are a matter of public record almost as soon as they happen.
