Transparent method
The formula
Worked example
Example inputs
How to interpret the result
A split changes how a position is divided into units, not what the position is actually worth. Doubling the share count while halving the price per share leaves the total position value exactly where it started, even though it can feel like something meaningful just happened to the holding.
Before you rely on it
What to check
Confirm the total position value before and after the split matches: shares times price should come out the same, aside from any separate price movement in the market that day.
The common error
Where people go wrong with stock split calculator
Reading a stock split as adding value to a position. It changes the number of shares and the price per share in exact inverse proportion; nothing about the underlying value of the holding moves because of the split itself.
Sensitivity evidence
How shares before split changes the shares after split
| Shares before split | Shares after split | Theoretical post-split price | Position value |
|---|---|---|---|
| 80 | 240 | $40 | $9,600 |
| 90 | 270 | $40 | $10,800 |
| 100worked example | 300 | $40 | $12,000 |
| 110 | 330 | $40 | $13,200 |
| 120 | 360 | $40 | $14,400 |
Every input, tested
Which input moves the shares after split most
| Input | Tested from | To | Shares after split at each end | Swing |
|---|---|---|---|---|
| Old-share ratio denominator | 0 | 2 | 0 to 150 | 150 (50%) |
| New-share ratio numerator | 2 | 4 | 200 to 400 | 200 (67%) |
| Shares before split | 90 | 110 | 270 to 330 | 60 (20%) |
| Price before split | $108 | $132 | 300 to 300 | none |
Two variables at once
Shares after split by shares before split and new-share ratio numerator
| Shares before split \ New-share ratio numerator | 1 | 3 | 5 |
|---|---|---|---|
| 80 | 80 | 240 | 400 |
| 90 | 90 | 270 | 450 |
| 100 | 100 | 300 | 500 |
| 110 | 110 | 330 | 550 |
| 120 | 120 | 360 | 600 |
Step by step
The worked example, input by input
| Input | Value used |
|---|---|
| Shares before split | 100 |
| Price before split | $120 |
| New-share ratio numerator | 3 |
| Old-share ratio denominator | 1 |
| Shares after split | 300 |
| Theoretical post-split price | $40 |
| Position value | $12,000 |
Where the inputs come from
Shares before the split is your holding, price before is the last price, and the ratio is stated as new shares for old, such as 3-for-1 with numerator 3 and denominator 1. For a reverse split such as 1-for-10, enter numerator 1 and denominator 10. The company announces the ratio and effective date in a press release and filings, and your broker adjusts the holdings automatically.
When the result stops applying
The theoretical price is what the math predicts, and the market price after a split can move for other reasons. Fractional shares from a split are usually paid out in cash, which is taxable. Reverse splits are often used by struggling companies to meet listing minimums, which is a warning sign in some cases. Options are adjusted by the exchange.
What to compare it with
Use the average stock cost calculator to recompute your basis after a split, and the stock profit calculator for a later sale. The market cap calculator shows that a split does not change company value. If a split leaves you with a fraction of a share, check how your broker handles it.
People also ask
Frequently asked questions
Does a stock split make me richer?
No. You own more shares at a proportionally lower price, so the value of your holding is the same immediately after the split.
Why do companies split their stock?
Mainly to lower the share price and make it look more accessible to small investors, and sometimes to make options and employee grants easier to manage.
What is a reverse stock split?
A reverse split combines shares, for example 1-for-10, raising the price per share. It is often used to keep a low-priced stock listed.