Rule 10b-18 Explained: Share Buybacks, US Regulation & Australian Impact

Rule 10b-18 is a US Securities and Exchange Commission (SEC) regulation introduced in 1982. In essence, it provides a 'safe harbour' for companies repurchasing their own shares on the open market. As long as they follow certain guidelines, companies are protected from accusations of share price manipulation.

• Volume limits: Buybacks on any single day can't exceed 25% of the average daily trading volume over the previous four weeks.

• Timing restrictions: Companies can't be the opening or last trade of the day, reducing the risk of dramatic price swings.

• Price constraints: Repurchases must not exceed the highest independent bid or last transaction price.

• Single broker rule: All buybacks in a day must be executed through one broker, making activity easier to monitor.

These guardrails are meant to keep markets fair, even as companies return capital to shareholders.

The landscape for buybacks is shifting in 2026. In the US, the SEC has faced pressure to tighten oversight, especially after a record $1.25 trillion in S&P 500 buybacks in 2023 and continued high activity in 2024. High-profile tech giants and banks have led the charge, sometimes facing criticism for prioritising buybacks over investment or wage growth.

Recent policy moves include:

• Buyback Excise Tax: The US government introduced a 1% excise tax on share buybacks in 2023, and 2026 discussions revolve around raising this to 4% or higher.

• Disclosure Reforms: The SEC in 2023 proposed stricter, real-time reporting of buyback activity, aiming for more transparency. These reforms are being phased in during 2024–2026.

• Global Influence: As the US sets the tone, other developed markets—including Australia—watch closely, especially as Australian companies like BHP and the big banks regularly use buybacks to manage capital and boost shareholder returns.

Australian regulators haven’t adopted a direct equivalent to Rule 10b-18, but the ASX and ASIC monitor buybacks for market fairness. With international investors increasingly active in both US and Australian markets, policy changes in one jurisdiction often spark debate in the other.

Rule 10b-18 isn’t just a technicality for US executives. Its rules, and the evolving scrutiny around buybacks, have direct and indirect impacts on Australian portfolios and listed companies:

• Portfolio Performance: Many Aussie super funds and ETFs have significant exposure to US equities, where buybacks can drive earnings per share and share price appreciation.

• Corporate Strategy: ASX-listed companies often look to US norms when designing their own buyback programs. Recent years have seen record buybacks in Australia, with BHP, CBA, and others returning billions to shareholders.

• Market Sentiment: Policy shifts—like the US excise tax and increased transparency—can influence global sentiment, valuations, and even prompt changes to local rules.

• Tax Implications: The US excise tax on buybacks has revived debate in Australia about the best way to reward shareholders—via buybacks, special dividends, or franking credits.

As 2026 unfolds, investors and companies need to stay alert to regulatory changes both at home and abroad. For example, if US buyback activity slows due to higher taxes or tighter rules, it could reduce demand for US stocks, affecting global benchmarks and superannuation returns.

Rule 10b-18 remains a foundation of US capital markets, offering a framework for buybacks that balances flexibility and fairness. In 2026, as scrutiny of buybacks intensifies and reforms gain traction, the implications will be felt far beyond Wall Street. Australian investors, super funds, and listed companies should watch these developments closely, as global finance grows ever more interconnected.