The Corporate Action Event-Type Taxonomy
Every corporate action a company can announce sorts into one of a handful of standard categories — mandatory, voluntary or mandatory-with-choice — and knowing which category an event falls into tells you immediately what a data feed, a back office and a shareholder each have to do about it.
A stock split, a cash dividend, a rights issue and a tender offer all get filed under the same broad heading — "corporate actions" — but they demand completely different handling from anyone downstream: a data vendor adjusting historical prices, a back office processing entitlements, or a shareholder who has to decide something. The industry's answer is a standard taxonomy that sorts every event into one of three categories, based on a single practical question: does the shareholder have to do anything?
The three categories
| Category | Does the shareholder choose? | Examples | What happens if you do nothing |
|---|---|---|---|
| Mandatory | No — it happens automatically to every holder | Cash dividend, stock split, merger (straight stock-for-stock) | Nothing to do; the event applies to your position automatically |
| Voluntary | Yes — requires an active election by a deadline | Tender offer, optional rights subscription | You default to not participating, which can mean losing value if the offer is favorable |
| Mandatory with choice | The event happens either way, but you pick the form | Cash-or-stock dividend, merger with a cash/stock election | A default option applies automatically if no election is made — often the less favorable one |
The category is the single most important fact about any corporate action, because it determines who bears the risk of inaction. In a mandatory event, doing nothing is correct by construction. In a voluntary event, doing nothing can mean forfeiting real economic value — a shareholder who ignores a tender offer deadline simply keeps the un-tendered shares, potentially at a worse price than the offer.
Mandatory, voluntary and mandatory-with-choice is not a bureaucratic distinction — it's the fault line between "the system handles this for you" and "you must act by a deadline or lose optionality." Every operational corporate-actions process is organized around detecting which bucket an event falls into as early as possible.
A narrower cut within mandatory events: does the price adjust?
Within the mandatory category, a second useful split is whether the event changes the number of shares or the reported price without changing what a holder owns economically (a 2-for-1 split, a stock dividend) versus whether it distributes value out of the company (a cash dividend, a spin-off). The first kind requires adjusting historical price series so a chart doesn't show a fake overnight crash; the second requires tracking an actual cash or asset entitlement. Both are "mandatory," but a data pipeline built to only adjust prices will silently mishandle the second kind if it isn't also tracking distributed value. The full lifecycle of dates that governs when an adjustment or entitlement actually applies is covered in Declaration, Record, Ex and Pay Dates.
Why this taxonomy exists as an industry standard, not a house convention
Corporate action data flows from an issuer's announcement, through data vendors, through custodians, to the end investor — a long chain with many participants who all need to agree on what kind of event they're looking at without re-reading the original legal announcement each time. ISO 20022 standardises event-type codes precisely so a mandatory dividend announced by a French company and a mandatory dividend announced by a US company are tagged identically in every system that touches them, which is what makes automated processing of corporate actions possible at scale. The practical consequences of getting this tagging wrong — a missed election, a misclassified event feeding a broken price adjustment — are covered in Corporate Action Data Feeds and the Golden Copy.
The most common real-world failure isn't misunderstanding the taxonomy — it's a data feed mis-tagging an event's category, most often mislabeling a voluntary or mandatory-with-choice event as fully mandatory. That error causes systems to silently skip the step where a human or an automated rule was supposed to make an election, and the default outcome quietly applies instead.
Further reading
- ISO 20022, Corporate Action Event Type Codes
- DTCC, Corporate Actions Reference Data