What Is a Stock Split? Ratios and Mechanics

A stock split changes a company's share count and per-share price at the same time, in a fixed ratio, and leaves the total value of every holding exactly where it was. In a 4-for-1 split each old share becomes four new ones, each priced near a quarter of the old level; nothing about the company itself, revenue, profits, who owns what fraction, moves at all. This guide covers the mechanics on real prints, the names that split recently, what prices did next, and what a decade of records makes plain: the most common US splits run the other way.

What is a stock split?

A stock split is a corporate action in which a company multiplies its share count by a fixed ratio and its share price divides by the same ratio. The board approves the ratio and an effective date, the first trading day at the new price and count. From that morning a holder of 100 shares in a 4-for-1 split owns 400 shares at about a quarter the prior price, the same dollar value, the same percentage of the company.

Everything share-denominated scales together. Shares outstanding and the stock float multiply by the ratio. The per-share dividend divides by it, leaving total dividend dollars unchanged. Listed option contracts are adjusted by the Options Clearing Corporation so existing positions keep their economics. Market capitalization, price times share count, does not move.

What does a split look like on the tape?

The cleanest way to see the mechanics is a real one: NVIDIA's 10-for-1 split, effective June 10, 2024. Here are the regular-session open and close prints on the last pre-split day and the first post-split day, straight from the minute-by-minute record:

SELECT toString(day) AS session,
       round(argMinIf(toFloat64(open), window_start, rth), 2) AS regular_open,
       round(argMaxIf(toFloat64(close), window_start, rth), 2) AS regular_close
FROM (
    SELECT toDate(toTimeZone(window_start, 'America/New_York')) AS day,
           window_start, open, close,
           toTimeZone(window_start, 'America/New_York') >= toDateTime(concat(toString(toDate(toTimeZone(window_start, 'America/New_York'))), ' 09:30:00'), 'America/New_York')
           AND toTimeZone(window_start, 'America/New_York') < toDateTime(concat(toString(toDate(toTimeZone(window_start, 'America/New_York'))), ' 16:00:00'), 'America/New_York') AS rth
    FROM global_markets.delayed_stocks_minute_aggs
    WHERE ticker = 'NVDA'
      AND window_start >= '2024-06-07 04:00:00'
      AND window_start < '2024-06-11 04:00:00'
)
GROUP BY day
ORDER BY day

NVDA closed the regular session at $1208.65 on 2024-06-07 and opened at $120.37 on 2024-06-10, one tenth the price, ten times the shares, the same company at the same valuation. On an unadjusted chart that morning looks like a 90% crash. It isn't one: most charting tools quietly rewrite history after a split, dividing every past price by the ratio, and the prints above are the prices as they actually traded.

Which companies have split their stock recently?

Most people want names, not aggregates. The table below lists every split executed since 2020 by thirteen widely held companies, plus the stock's move over its next 21 trading sessions (about a month), measured from the split-day close, and the same-window move in SPY, the S&P 500 tracker.

SELECT ticker, executed_on, ratio, recorded_as, stock_21_sessions_pct, spy_21_sessions_pct
FROM (
    WITH events AS (
        SELECT ticker, execution_date,
               concat(toString(toInt32(split_to)), '-for-', toString(toInt32(split_from))) AS ratio,
               if(adjustment_type = 'stock_dividend', 'stock dividend', 'forward split') AS recorded_as
        FROM global_markets.stocks_splits
        WHERE ticker IN ('AAPL', 'TSLA', 'GOOGL', 'AMZN', 'NVDA', 'WMT', 'CMG', 'AVGO', 'SMCI', 'LRCX', 'DECK', 'ORLY', 'NFLX')
          AND execution_date >= '2020-01-01' AND execution_date <= '2026-06-30'
          AND split_to > split_from
    ),
    daily AS (
        SELECT ticker,
               toDate(toTimeZone(window_start, 'America/New_York')) AS d,
               argMaxIf(toFloat64(close), window_start,
                        (toHour(toTimeZone(window_start, 'America/New_York')) * 60 + toMinute(toTimeZone(window_start, 'America/New_York'))) BETWEEN 570 AND 959) AS close_rth
        FROM global_markets.delayed_stocks_minute_aggs
        WHERE ticker IN (SELECT ticker FROM events UNION ALL SELECT 'SPY')
          AND window_start >= '2020-08-01 00:00:00' AND window_start < '2026-01-15 00:00:00'
        GROUP BY ticker, d
        HAVING close_rth > 0
    ),
    series AS (
        SELECT ticker, arraySort(x -> x.1, groupArray((d, close_rth))) AS dc
        FROM daily
        GROUP BY ticker
    ),
    spy AS (
        SELECT dc AS spy_dc FROM series WHERE ticker = 'SPY'
    )
    SELECT e.ticker AS ticker,
           toString(e.execution_date) AS executed_on,
           e.ratio AS ratio,
           e.recorded_as AS recorded_as,
           arrayFirstIndex(x -> x.1 >= e.execution_date, s.dc) AS idx,
           arrayFirstIndex(x -> x.1 >= e.execution_date, spy_dc) AS sidx,
           round((s.dc[idx + 21].2 / s.dc[idx].2 - 1) * 100, 1) AS stock_21_sessions_pct,
           round((spy_dc[sidx + 21].2 / spy_dc[sidx].2 - 1) * 100, 1) AS spy_21_sessions_pct,
           e.execution_date AS ed
    FROM events e
    JOIN series s ON s.ticker = e.ticker
    CROSS JOIN spy
    ORDER BY ed DESC, ticker ASC
)

The most recent name here is NFLX, a 10-for-1 split effective 2025-11-17; Chipotle's 50-for-1 (2024-06-26) is the largest ratio on the list. Announcements in this group typically cite accessibility: a lower per-share price makes round lots and 100-share option contracts smaller-ticket items.

Stock split vs. stock dividend

The recorded-as column resolves a common confusion: several famous "splits", Tesla's 5-for-1 of 2020-08-31, Alphabet's 20-for-1 of 2022-07-18, NVIDIA's 4-for-1 of 2021-07-20, were structured as stock dividends, not splits. A stock dividend distributes additional shares the way a cash dividend distributes cash, Tesla's delivered four extra shares per share held. For the holder the arithmetic is identical to a forward split, more shares, proportionally lower price, same dollar value, no tax due in the routine case, which is why headlines call them all splits. The differences are accounting and legal form: a stock dividend capitalizes retained earnings, a split adjusts par value, and neither moves money out of the company the way a cash dividend does.

What split ratios do companies actually use?

Split announcements get described loosely; the records are specific. Counting whole-number forward splits across all US-listed securities over the trailing year:

SELECT concat(toString(toInt32(split_to)), '-for-1') AS ratio,
       count() AS splits
FROM global_markets.stocks_splits
WHERE execution_date >= '2025-07-01' AND execution_date <= '2026-06-30'
  AND split_from = 1 AND split_to >= 2 AND split_to = round(split_to)
GROUP BY ratio
ORDER BY splits DESC
LIMIT 6

The most common forward ratio over the window was 2-for-1, with 76 executions, followed by 3-for-1 (51). Simple small ratios dominate; the double-digit ratios that make headlines, like NVIDIA's 10-for-1 above, are a minority.

Do stocks go up after a split?

The most-searched follow-up question, and the notable-splits table already hints at the answer: NFLX traded -14.1% over the 21 sessions following its split while SPY moved +0.8%, Chipotle printed -24.3% following its 50-for-1, and Alphabet gained 11.7% in a tape where SPY gained 12.5%. To get past anecdotes: every whole-number forward split on a US-listed security in 2025 with full minute-bar coverage in our warehouse, measured the same way, from the split-day close, entirely in post-split prices:

WITH events AS (
    SELECT ticker, execution_date
    FROM global_markets.stocks_splits
    WHERE execution_date >= '2025-01-01' AND execution_date <= '2025-12-31'
      AND adjustment_type = 'forward_split' AND split_from = 1
      AND split_to >= 2 AND split_to = round(split_to)
),
daily AS (
    SELECT ticker,
           toDate(toTimeZone(window_start, 'America/New_York')) AS d,
           argMaxIf(toFloat64(close), window_start,
                    (toHour(toTimeZone(window_start, 'America/New_York')) * 60 + toMinute(toTimeZone(window_start, 'America/New_York'))) BETWEEN 570 AND 959) AS close_rth
    FROM global_markets.delayed_stocks_minute_aggs
    WHERE ticker IN (SELECT ticker FROM events UNION ALL SELECT 'SPY')
      AND window_start >= '2025-01-01 00:00:00' AND window_start < '2026-03-01 00:00:00'
    GROUP BY ticker, d
    HAVING close_rth > 0
),
series AS (
    SELECT ticker, arraySort(x -> x.1, groupArray((d, close_rth))) AS dc
    FROM daily
    GROUP BY ticker
),
spy AS (
    SELECT dc AS spy_dc FROM series WHERE ticker = 'SPY'
),
per_event AS (
    SELECT e.ticker AS tkr,
           arrayFirstIndex(x -> x.1 >= e.execution_date, s.dc) AS idx,
           arrayFirstIndex(x -> x.1 >= e.execution_date, spy_dc) AS sidx,
           s.dc AS dc, spy_dc
    FROM events e
    JOIN series s ON s.ticker = e.ticker
    CROSS JOIN spy
),
measured AS (
    SELECT tkr,
           (dc[idx + 5].2 / dc[idx].2 - 1) * 100 AS r5,
           (dc[idx + 21].2 / dc[idx].2 - 1) * 100 AS r21,
           (spy_dc[sidx + 21].2 / spy_dc[sidx].2 - 1) * 100 AS spy21
    FROM per_event
    WHERE idx > 0 AND length(dc) >= idx + 21
      AND sidx > 0 AND length(spy_dc) >= sidx + 21
      AND dc[idx].2 > 0
)
SELECT count() AS splits_measured,
       round(quantileDeterministic(0.5)(r5, cityHash64(tkr)), 1) AS median_5_session_pct,
       round(quantileDeterministic(0.5)(r21, cityHash64(tkr)), 1) AS median_21_session_pct,
       round(100.0 * countIf(r21 > 0) / count(), 0) AS pct_up_after_21_sessions,
       round(quantileDeterministic(0.5)(spy21, cityHash64(tkr)), 1) AS median_spy_21_session_pct
FROM measured

Across 44 splits, the median move was -0.9% five sessions after the split day and -1.5% after 21 sessions; only 45% of the group stood higher a month out, while SPY's median move over the same windows was +1.6%. One year's tape is not a law, the list above includes post-split gains, but it sits squarely against the folk wisdom that a split hands a stock a pop. Nothing in the mechanics says it should: same pizza, more slices.

Does a split make a stock easier to trade?

The accessibility rationale is testable. If a lower per-share price brings in more trading, it shows up in volume. NVIDIA's 10-for-1 again, twenty sessions each side:

WITH daily AS (
    SELECT toDate(toTimeZone(window_start, 'America/New_York')) AS d,
           sum(toFloat64(volume)) AS shares,
           sum(toFloat64(close) * toFloat64(volume)) AS dollars
    FROM global_markets.delayed_stocks_minute_aggs
    WHERE ticker = 'NVDA'
      AND window_start >= '2024-05-08 00:00:00' AND window_start < '2024-07-12 00:00:00'
    GROUP BY d
),
ranked AS (
    SELECT d, shares, dollars,
           d >= toDate('2024-06-10') AS post,
           row_number() OVER (PARTITION BY d >= toDate('2024-06-10')
                              ORDER BY if(d < toDate('2024-06-10'), -toUInt32(d), toUInt32(d))) AS rn
    FROM daily
)
SELECT if(post = 0, 'Last 20 sessions before the split', 'First 20 sessions from the split') AS phase,
       count() AS sessions,
       round(avg(shares) / 1e6, 1) AS avg_daily_shares_millions,
       round(avg(dollars) / 1e9, 1) AS avg_daily_dollars_billions
FROM ranked
WHERE rn <= 20
GROUP BY phase, post
ORDER BY post

Share volume jumped: an average of 44.1 million shares a day before, 292.4 million from the split. But shares are the wrong unit, a post-split share carries a tenth of the dollars. Count dollars instead and the comparison flips: $46.9 billion a day before, $37.1 billion from the split day on, slightly less. More tickets changed hands at smaller sizes, each still crossing the bid-ask spread; the dollars at work did not grow.

Reverse splits are more common than forward splits

A reverse split runs the arithmetic the other way: share count divides, price multiplies. A reverse stock split of 1-for-10 turns 1,000 shares at $0.50 into 100 shares at $5.00. Exchanges hold listed stocks to minimum-price standards, and a reverse split is the standard tool for climbing back above them, full mechanics in the linked guide.

What most explainers miss is the score. Counting every split executed on US-listed securities over the last ten full years:

SELECT sum(forward_splits) AS forward_total,
       sum(reverse_splits) AS reverse_total,
       round(sum(reverse_splits) / sum(forward_splits), 2) AS reverse_per_forward,
       countIf(reverse_splits > forward_splits) AS years_reverse_ahead
FROM (
    SELECT toYear(execution_date) AS year,
           countIf(split_to > split_from) AS forward_splits,
           countIf(split_from > split_to) AS reverse_splits
    FROM global_markets.stocks_splits
    WHERE execution_date >= '2016-01-01' AND execution_date < '2026-01-01'
    GROUP BY year
)

Reverse splits outnumbered forward splits 7109 to 4122 across 2016-2025, about 1.72 reverse splits for every forward one, and the reverse side won the annual count in 9 of the ten years. Year by year, with 2026's first half included:

SELECT toYear(execution_date) AS year,
       countIf(split_to > split_from) AS forward_splits,
       countIf(split_from > split_to) AS reverse_splits
FROM global_markets.stocks_splits
WHERE execution_date >= '2016-01-01' AND execution_date <= '2026-06-30'
GROUP BY year
ORDER BY year

In 2025, the last full year, the count ran 1038 reverse against 429 forward, and the first half of 2026 held the pattern at 597 reverse to 233 forward. The one close year was 2018, at 529 forward to 526 reverse. Forward splits concentrate in large companies whose prices have climbed for years; reverse splits are routine housekeeping across the market's long tail of small, low-priced names, and the tail has more members than the head.

Record date, effective date, and your cost basis

A split announcement names three dates: the announcement date (the ratio is declared), the record date (which holders are entitled on the company's books), and the effective date, the morning the stock opens at the new price and your account shows the new count. A common worry is needing to own the stock by the record date to "qualify"; the machinery handles it. Shares bought between the record and effective dates carry the entitlement with them (brokers track this with due bills), and shares sold pass it to the buyer. Nothing to sign up for, nothing to claim.

Cost basis rescales the same way the price does. Say you bought 100 shares at $40, a $4,000 position. After a 4-for-1 split you hold 400 shares and the same $4,000 spreads to $10 per share; sell 100 of them later and the cost against that sale is $1,000.

Odd ratios leave fractions. A 3-for-2 split turns 25 shares into 37.5, and companies rarely issue half shares: the broker delivers 37 whole shares and the leftover half arrives as cash in lieu, at a post-split price of, say, $20, a deposit of $10. That small forced sale is a taxable event on the fraction.

How a split hits a price-weighted index

In a capitalization-weighted index like the S&P 500 a split is a non-event, market cap and index weight do not move. A price-weighted index like the Dow Jones Industrial Average is different. Each member's weight there is its share price as a fraction of the sum of all thirty prices, and a split shrinks both. On the effective morning the publisher adjusts the Dow divisor, the number the price sum is divided by, to keep the index level continuous; from then on the split stock carries proportionally less weight, a 4-for-1 split cutting its Dow influence to roughly a quarter.

Stock split FAQ

Does a stock split change the value of my investment?

No. The share count multiplies by the ratio and the price divides by it, and the product, your position's dollar value, is unchanged, along with your percentage ownership. The split is not a taxable event under US rules; cost basis simply spreads across the new share count.

Do stocks usually go up after a stock split?

The records offer no automatic pop. Across 2025's 44 measured forward splits, the median move was -1.5% over the 21 sessions from the split day and only 45% stood higher, while SPY's median same-window move was +1.6%.

What is the difference between a stock split and a stock dividend?

Both deliver extra shares in proportion to what you hold, more shares, a proportionally lower price, unchanged value. The difference is legal and accounting form; several famous "splits," including Tesla's 2020 and Alphabet's 2022 actions, were structured as stock dividends. Neither is a cash dividend, which pays out actual money.

What happens to dividends and options when a stock splits?

Both are adjusted automatically. The per-share dividend divides by the split ratio, leaving total dividend dollars unchanged. Listed options are adjusted by the Options Clearing Corporation: strikes divide by the ratio and contract counts multiply, preserving each position's economics.

Do I have to do anything when a stock I own splits?

No. Brokers apply splits automatically on the effective date: the new share count and rescaled per-share cost basis appear in the account with no action needed. Fractional results from odd ratios are typically paid out as cash in lieu.

Every count above is a stored, versioned query, expand the SQL under any panel to see exactly what was measured, or run the same questions in plain English on the Strasmore terminal.