Stock Split Calculator
See your new share count, adjusted price and cost basis after a forward or reverse stock split.
Quick answer
In an a-for-b stock split every b shares become a shares, so shares are multiplied by a / b and price is divided by a / b. Position value is unchanged, and cost basis per share scales by the same factor.
Stock Split Calculator
For a-for-b, enter a here. 2-for-1: a = 2. Reverse 1-for-10: a = 1.
For a-for-b, enter b here. 2-for-1: b = 1. Reverse 1-for-10: b = 10.
Leave blank to skip the cost basis rows.
Split Type
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Whole Shares After
Price After Split
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Cash For Fraction
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Position Value (Unchanged)
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Cost Basis Per Share After
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Educational only, not trading or investment advice. Figures are estimates.
Before and After
| Item | Before | After |
|---|
Assumptions & method
- Multiplier = a ÷ b for an a-for-b split. Shares after = shares × a ÷ b; price after = price ÷ (a ÷ b).
- Whole shares are rounded down. The leftover fraction is assumed to be paid in cash at the post-split price.
- Position value = whole shares × new price + cash for the fraction. It equals shares × old price.
- Cost basis per share after = basis ÷ multiplier. The total cost basis does not change.
- Not included: market moves after the split, broker rounding rules, fees and any tax on cash paid in lieu.
- Educational only; this is not trading or investment advice.
Results are estimates based on the figures you enter. They are not guarantees and not financial advice.
How a stock split works
A stock split is an accounting change to the number of shares, not to the value of the company. In an a-for-b split, every b shares you hold become a shares, so the multiplier is a ÷ b. If it is above 1 the split is forward and the price per share falls by the same factor. If it is below 1 the split is a reverse split and the price rises. Because shares and price move in opposite directions, the value of your position stays the same. Your cost basis per share is divided by the multiplier, and any leftover fraction is usually paid in cash.