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To check a suspected stock split, compare the event’s ratio and effective date with the raw closing prices immediately before and after it. If the ratio is expressed as new shares per old share, divide the pre-split price by that factor; the result should be in the same general price range as the first post-split close, allowing for normal market movement. This is a mechanical plausibility check—not a return calculation, and not proof that a vendor’s data are correct.
What a split changes—and what it does not
A stock split changes the number of shares and the per-share price scale in opposite directions. In an ordinary split, shareholders receive more or fewer shares while the price per share adjusts to reflect the new share basis. CRSP says an ordinary split has no effect on the company’s market capitalization by itself in its 2024 CRSP Market Indexes Methodology Guide.
That does not mean the stock’s market price stays fixed across the event. Trading continues, and the market can move between the last pre-event close and the first post-event close. A split factor describes a change in share basis; by itself, it says nothing about the investment’s gain or loss.
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Keep the security identity consistent
Confirm that the records refer to the same security throughout the period. A ticker can change, so use a durable identifier and historical identity information when available rather than assuming the symbol alone identifies the same security over time.
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Match the event record to daily prices
Retrieve daily raw or unadjusted OHLCV data—the open, high, low, close, and volume—and a split-event record for the same security and date range. Nasdaq Data Link documents the Sharadar SEP price table and ACTIONS table in its Sharadar Equity Prices documentation.
Write down the event’s effective or ex-distribution date and the ratio convention used by the record. Express the ratio as new shares divided by old shares. For example, a 3-for-2 split means 3 new shares for every 2 old shares, so the factor is 3 ÷ 2 = 1.5. Nasdaq’s documented example uses new float divided by old float.
Verify what “price” means in each series
Do not compare fields until you know their adjustment scope. Nasdaq Data Link documents these distinctions for its Sharadar data:
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- Unadjusted close: includes no split, dividend, or spinoff adjustment.
- OHLC and volume: adjusted for stock splits and stock dividends.
- Close-adjusted: adjusted for splits, cash dividends, and spinoffs.
These fields answer different questions. A retrospectively adjusted value is not the price actually recorded for a historical trading date. If the question is what the raw daily record shows, use the unadjusted field; if it is how a vendor presents history on an adjusted share basis or for broader return analysis, use the relevant adjusted field and label it precisely.
Compare prices using the split factor
For a split ratio r expressed as new shares per old share, the mechanical ex-event price scale is approximately:
post-split price ≈ pre-split price / r
For a 3-for-2 split, r = 1.5. Divide the last pre-event raw close by 1.5, then compare that value with the first post-event raw close. The two need not match exactly: ordinary market movement can change the price between sessions. Treat the comparison as a scale check, not as a test that prices or returns must be equal.
Before judging a mismatch, confirm that the split has not been applied using the inverse factor. A 3-for-2 event can be recorded as 1.5 new shares per old share or, under a different convention, as 2 old shares per 3 new shares. Convert the record to new shares divided by old shares before doing the calculation.
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CRSP says split events are applied on the Ex-Distribution Date. If the price series and event record use different date conventions—or the wrong session has been treated as the event date—a valid factor can appear to produce the wrong result. Compare the event date with the sessions immediately before and after it, and establish which observation the provider treats as ex-event.
Look for missing sessions or gaps in price history around the event. CRSP documents that adjusted values can be missing when an event is absent or uncertain across a gap in trading history. A discontinuity or missing adjusted value in that circumstance does not, by itself, show that the arithmetic is wrong; it may indicate incomplete event coverage.
Inspect cumulative adjustment factors when available
Some vendors provide cumulative factors that transform historical observations onto a chosen adjustment basis. CRSP describes the general relationships as:
adjusted price A(t) = raw price P(t) / C(t)
adjusted shares or volume A(t) = raw shares or volume P(t) * C(t)
Here, C(t) is the cumulative factor determined by events between an observation and the adjustment base date. The base date is the anchor, and its observation remains unadjusted. The adjusted value is a calculated historical value, not an observed market transaction. CRSP’s Chapter 3: CRSP Calculations documents the factor direction and event-timing approach.
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Across a split, check that the factor’s direction is consistent with the transformation: historical prices are divided by the cumulative factor, while shares and volume are multiplied. Do not assume two providers’ adjusted values should match until you have checked their adjustment base dates and which events they include.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Use shares and volume as a supporting check
Where share counts are available, verify that their adjusted direction is consistent with the price adjustment. CRSP’s method multiplies shares and volume by the cumulative factor while dividing price by it. This can help identify a reversed factor or a field-definition mismatch.
Volume is not expected to equal a fixed multiple across the event: it also reflects how much trading took place. Use it as a consistency check, not a deterministic equality. Also note that a provider’s treatment can differ by event type; CRSP’s split-event framework includes some distributions with price factors, while shares and volume are adjusted only for stock splits and stock dividends.
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A practical verification checklist
- Pin down the security: match a durable identifier and historical identity across the full date range, especially if the ticker changed.
- Collect comparable records: obtain daily raw OHLCV and the event record for the same security, including the effective or ex-distribution date.
- Normalize the ratio: express it as new shares divided by old shares; convert an inverse convention before using it.
- Confirm the fields: distinguish unadjusted prices from split-adjusted and broader dividend- or spinoff-adjusted series.
- Check the adjacent closes: divide the last pre-event raw close by the factor and compare it with the first post-event raw close, allowing for market movement.
- Check factor direction and anchor: if cumulative factors are supplied, confirm that prices are divided, shares and volume multiplied, and the adjustment base date is understood.
- Investigate apparent breaks: check for missing sessions, ticker or identifier changes, reverse splits, stock dividends, and other price-factor events.
- Report the basis: identify the provider, field, date convention, ratio, and any continuity or coverage limitation when showing an example.
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