About the Stock Split Calculator
This stock split calculator shows what happens to your holding when a company splits its shares. Enter how many shares you own, the pre-split price, your original cost per share and the split ratio — for example 4-for-1 or a 1-for-10 reverse split — and it returns your new share count, the adjusted price, your adjusted cost basis per share and the value of the position.
It is handy for investors checking that a broker applied a split correctly, updating a spreadsheet or tax records, or understanding a reverse split announcement. For reverse splits it also shows the fractional share you would be left with and the approximate cash in lieu most brokers pay for it.
A split does not change what your position is worth: the price adjusts in exact proportion to the share count, and your total cost basis is simply spread across the new number of shares. Cash in lieu is estimated at the post-split price; the actual amount depends on the price the company or transfer agent realizes, and it can be a small taxable sale.
With the default inputs, the shares after the split is 1,000. Change any value above to recalculate instantly.
How to use the stock split calculator
- 1Enter how many shares you own before the split.
- 2Enter the pre-split share price and your original cost per share.
- 3Enter the split ratio — e.g. 4 and 1 for a 4-for-1, or 1 and 10 for a 1-for-10 reverse split.
- 4Read your new share count, adjusted price and adjusted cost basis.
- 5For reverse splits, check the fractional share and estimated cash in lieu.
Formula and method
A split ratio of a-for-b means every b shares you own become a shares. Your new share count is the old count times a ÷ b, and the market price and your per-share cost basis are divided by the same factor, so the total value S × P and total cost basis S × B stay the same.
In a reverse split (a smaller than b) the count usually no longer divides evenly. The whole shares are kept, and the remaining fraction is normally sold with the proceeds paid as cash in lieu; this tool estimates it as the fraction times the post-split price.
- S
- Shares owned before the split
- P
- Share price before the split
- B
- Cost basis per share before the split
- a
- New shares in the split ratio
- b
- Old shares in the split ratio
Worked examples
10-for-1 split: 100 shares at $600
A 10-for-1 split turns 100 shares into 1,000 and cuts the price from $600 to $60. The $450 cost per share becomes $45, so the $45,000 total basis and $60,000 position value do not change.
1-for-10 reverse split with a fractional share
Dividing 255 shares by 10 gives 25.5 shares. The price rises from $1.20 to $12 and the cost per share from $3 to $30. You keep 25 whole shares and the half share is sold for about $6 cash in lieu.
3-for-2 split on 75 shares
A 3-for-2 split multiplies holdings by 1.5, so 75 shares become 112.5. The price drops from $90 to $60 and cost per share from $60 to $40. If fractions are not kept, the half share is paid out as about $30.
Frequently asked questions
Does a stock split change the value of my investment?+
No. A split changes only how many pieces the company is cut into. The price per share falls (or rises, for a reverse split) in exact proportion, so your total position value is the same the moment the split takes effect.
What happens to my cost basis after a stock split?+
Your total cost basis stays the same and is spread across the new number of shares. In a 2-for-1 split, a $100 cost per share becomes $50 per share; your purchase date and holding period carry over.
Is a stock split taxable?+
A normal stock split is generally not a taxable event in the US because you receive no cash and your total basis is unchanged. Cash received in lieu of a fractional share is treated as a sale of that fraction and can create a small gain or loss.
What is a reverse stock split?+
A reverse split combines shares, for example 1-for-10 turns every 10 shares into 1 at ten times the price. Companies often do it to lift a low share price above an exchange’s minimum listing requirement.
What happens to options when a stock splits?+
Listed options are adjusted by the Options Clearing Corporation so the position is economically unchanged. For even splits like 2-for-1 you usually get more contracts at a lower strike; odd ratios produce adjusted contracts with non-standard deliverables.
Results are estimates for educational purposes and are not financial advice. Rates, fees and terms vary — confirm with your lender or a licensed advisor before making decisions.