Stock Split Calculator
When a company announces a stock split, every shareholder receives additional shares in proportion to their existing holdings, and the price per share is adjusted downward so the total market value remains unchanged. This calculator helps you quickly determine your new share count, new price per share, and adjusted cost basis after any forward or reverse split. Enter the number of shares you currently hold, the current price per share, your average cost basis per share, and the split ratio. Common split ratios include 2-for-1, 3-for-1, and 3-for-2. To model a reverse split (for example 1-for-5), enter the ratio as a decimal such as 0.2. Understanding how splits affect your cost basis is essential for accurately reporting capital gains when you eventually sell your shares.
Stock split formulas
New Shares = Current Shares x Split Ratio
New Price = Current Price / Split Ratio
Adjusted Cost Basis = Cost Basis / Split Ratio
Total Value = New Shares x New Price (unchanged)
For a reverse split, the split ratio is less than 1. For example, a 1-for-5 reverse split has a ratio of 0.2.
Common split ratios explained
- 2-for-1 split: each share becomes 2 shares; price is halved. Enter ratio 2.
- 3-for-1 split: each share becomes 3 shares; price is divided by 3. Enter ratio 3.
- 3-for-2 split: every 2 shares become 3 shares; price is multiplied by 2/3. Enter ratio 1.5.
- 1-for-5 reverse split: every 5 shares become 1; price is multiplied by 5. Enter ratio 0.2.
- 10-for-1 split (e.g., Apple 2020): enter ratio 10. Price becomes one-tenth of original.
Stock split: frequently asked questions
What is a stock split?
A stock split increases the number of outstanding shares by issuing new shares to existing shareholders in a fixed ratio. The company's total market capitalisation stays the same; only the number of shares and price per share change. A 2-for-1 split doubles your shares and halves the price.
Does a stock split change my investment value?
No. On the day of the split your total holding value remains identical. If you had 100 shares at $200 each ($20,000 total) and a 4-for-1 split occurs, you now have 400 shares at $50 each, still worth $20,000. Value is preserved; only the per-share metrics change.
How does a split affect my cost basis?
Your total cost basis is unchanged, but the per-share cost basis is adjusted proportionally. If you paid $100 per share before a 2-for-1 split, your adjusted cost basis per share becomes $50. This matters for calculating capital gains when you sell.
What is a reverse stock split?
A reverse split reduces the number of shares and increases the price proportionally. Enter a ratio less than 1 (e.g., 0.5 for a 1-for-2 reverse split) in this calculator to model reverse splits. Companies use reverse splits to avoid delisting from exchanges with minimum price requirements.
How do fractional shares work in a split?
If a split results in a fractional share, your broker typically pays cash in lieu of the fraction. For example, if you hold 15 shares and a 3-for-2 split would give you 22.5 shares, you would receive 22 shares plus a cash payment for the 0.5 share at the new price.
Official sources
- IRS Publication 550: Investment Income and Expenses - Stock Splits.
- SEC EDGAR: Company Filings Search.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.