corporate actions

A corporate action is any decision an issuer takes that changes what a share represents: a split multiplies share count, a dividend moves cash out of the price, a reorganization can replace identifiers altogether. Two data shapes follow.

Calendars announce dated events ahead of time. Euronext publishes index weightings and corporate action calendars updated daily or as published; Investing.com runs dividend and splits calendars among its seven calendar families. Adjusted histories rewrite the past: Tiingo's daily rows carry the 'corporate-actions' and 'adjusted-prices' tags, delivering back-adjusted series so returns compute cleanly across event dates.

Unadjusted prices make returns lie. Buy a raw close series, hold across a 2-for-1 split, and your backtest books a fictional -50% day.

• Adjustment method must be stated. Tiingo explicitly brands 'corporate-action-adjusted histories'; a vendor that cannot name its method is selling ambiguity.
• Forward events need a calendar, not a history. Euronext refreshes calendars daily or as published - stale feeds miss ex-dates that drive rebalancing.
• Calendars are cheap to test. With 32.9% of cataloged datasets offering an official API, you can usually pull today's dividend list before committing to a subscription.

1. Reconcile a known split. Take one ticker, one event date, and check the provider's adjusted series produces a flat return on the ex-date.

1. Count the calendar families. Investing.com exposes seven calendar types including dividends and splits - breadth here tells you how much workflow one feed covers.

1. Check update cadence in writing. Euronext commits to daily updates for index weightings and corporate actions; anything slower risks missed announcements.

1. Verify identifier continuity. Reorganizations change tickers and IDs, so ask how the vendor links old and new instruments over time.

1. Separate gross from net adjustments. Dividend handling differs between total-return and price-return series - the distinction should be documented, not discovered.

Market-data concepts that pair with corporate actions: - end of day prices — End-of-day prices are one summary bar per instrument per trading session, the baseline product of market data APIs. - market calendars — Market calendars schedule the dated events investors track: earnings, dividends, splits, IPOs, futures expiries, holidays and economic releases. - reference data — Reference data is the descriptive master record per instrument - identifiers, venue, currency, status - kept apart from price history.