Stock Split Calculator

Shares held before the split

Cost basis per share

Share price before the split

Optional: shows the price the market should open at after the split.

Split ratios, oldest first

New shares	For old shares	Remove

Shares after the split —

Cost basis per share after: —
Total cost basis (unchanged): —
Combined split ratio: —
Fractional share left over: —
Adjusted share price: —

After a stock split, multiply your shares by the split ratio and divide your cost basis per share by the same ratio; the total basis does not change. 100 shares bought at $50 become 200 shares at $25 after a 2-for-1 split, still $5,000 in total.

About this tool

A split changes how many shares you hold and what each one cost on paper, but not what the position is worth or what you paid for it. Investors reconciling broker statements, tracking cost basis by hand, or reading an old purchase price against today's quote need the adjusted numbers. Enter the shares you held, your cost per share and every split since you bought, oldest first, including reverse splits such as 1-for-10. The result gives the new share count, the basis per share, the combined ratio and any fractional share a reverse split leaves behind. It does not model cash paid in lieu of fractions or the tax treatment of that cash.

How to use it

Enter your holding
Type the shares you held before the split and the cost basis you paid per share.
Add each split ratio
Write a 3-for-2 split as 3 new shares for 2 old. Use Add another split for later splits, oldest first.
Add the pre-split price
Optionally enter the share price before the split to see where it should trade afterwards.
Read the table
Each row shows the share count and basis per share after that split.

Examples

100 shares, 2-for-1 split

Shares held before the split: 100
Cost basis per share: 50
Share price before the split: 120
Split ratios, oldest first: 2 × 1

Result Shares after the split: 200
Cost basis per share after: 25.0000
Total cost basis (unchanged): 5,000.00
Combined split ratio: 2
Fractional share left over: 0
Adjusted share price: 60.0000

Combined ratio = 2-for-1 = 2
Shares after = 100 × 2 = 200
Cost per share after = 50.00 ÷ 2 = 25.0000
Total cost basis stays 5,000.00
Price after = 120.00 ÷ 2 = 60.0000

The holding doubles to 200 shares while the $5,000 basis is spread over twice as many shares, $25 each.

A 4-for-1 then a 3-for-2

Shares held before the split: 10
Cost basis per share: 400
Split ratios, oldest first: 4 × 1; 3 × 2

Result Shares after the split: 60
Cost basis per share after: 66.6667
Total cost basis (unchanged): 4,000.00
Combined split ratio: 6
Fractional share left over: 0

Combined ratio = 4-for-1 × 3-for-2 = 6
Shares after = 10 × 6 = 60
Cost per share after = 400.00 ÷ 6 = 66.6667
Total cost basis stays 4,000.00

Ten shares become 40, then 60. The combined ratio is 6, so the $400 basis per share falls to about $66.67.

1-for-10 reverse split

Shares held before the split: 105
Cost basis per share: 2
Split ratios, oldest first: 1 × 10

Result Shares after the split: 10.5
Cost basis per share after: 20.0000
Total cost basis (unchanged): 210.00
Combined split ratio: 0.1
Fractional share left over: 0.5

Combined ratio = 1-for-10 = 0.1
Shares after = 105 × 0.1 = 10.5
Cost per share after = 2.00 ÷ 0.1 = 20.0000
Total cost basis stays 210.00

105 shares become 10.5; the half share is usually paid out in cash, and the basis rises to $20 per share.

How it is calculated

R = Π (new ÷ old); shares after = shares × R; basis per share after = basis ÷ R

new ÷ old: one split ratio, e.g. 2 ÷ 1 for a 2-for-1 split or 1 ÷ 10 for a 1-for-10 reverse split
R: combined ratio, the product of every split since purchase
basis: what you paid per share, including fees if you track them

Splits apply one after another, so their ratios multiply. The share count is multiplied by the combined ratio and the per-share basis and price are divided by it, which keeps the total basis and the market value of the position the same. A reverse split has a ratio below 1 and can leave part of a share.

Sources

Stock Splits — Investor.gov (U.S. Securities and Exchange Commission)

When not to use it

Spin-offs and stock dividends of a different company allocate basis by fair value, not by a simple ratio.
For a tax return, rely on the adjusted basis your broker reports, which also covers cash paid for fractions.

Common mistakes

Entering a reverse split the wrong way round, such as 10 for 1 instead of 1 for 10.
Adjusting the share count but leaving the old per-share basis, which overstates the total paid.
Skipping an earlier split when a holding has been split more than once.

Frequently asked questions

Does a stock split change the value of my investment?

No. A split divides the same company into more or fewer shares. Right after the split, shares times price equals what it was before, ignoring normal market movement that day.

How is a 3-for-2 split worked out?

Each 2 shares become 3, so the ratio is 1.5. 100 shares become 150 and a $45 basis per share becomes $30. The total basis stays $4,500.

What happens to fractional shares in a reverse split?

A 1-for-10 reverse split on 105 shares gives 10.5 shares. Most companies and brokers pay cash for the half share rather than keep it, and that cash payment can count as a sale of the fraction.

Is a stock split taxable?

A normal split is generally not a taxable event in the United States; it only reallocates your basis across the new share count. Cash received for fractional shares is treated differently, so check your broker's tax documents.

Do I need to adjust old purchase prices for splits?

Yes, if you compare them with today's quote. Historical price charts are usually split-adjusted, so a purchase price that was not adjusted will look far higher or lower than it really was.

How do I enter several splits?

Add one row per split in the order they happened. The ratios multiply, so a 4-for-1 followed by a 3-for-2 equals a single 6-for-1 split.

Cite this tool

Using this tool in an assignment, article or report? Copy a citation, or a link for your website.

APA

Tools Directory Editorial Team. (2026, October 26). Stock Split Calculator. Tools Directory. Retrieved October 26, 2026, from https://tools.milunir.com/finance/stocks-and-dividends/stock-split-calculator/

MLA

Tools Directory Editorial Team. “Stock Split Calculator.” Tools Directory, 26 Oct. 2026, https://tools.milunir.com/finance/stocks-and-dividends/stock-split-calculator/. Accessed 26 Oct. 2026.

Chicago

Tools Directory Editorial Team. “Stock Split Calculator.” Tools Directory. Last modified October 26, 2026. Accessed October 26, 2026. https://tools.milunir.com/finance/stocks-and-dividends/stock-split-calculator/.

Link

<a href="https://tools.milunir.com/finance/stocks-and-dividends/stock-split-calculator/">Stock Split Calculator – Tools Directory</a>