Stock Split Adjuster
Recalculate share quantity and cost per share after a forward or reverse stock split, with a check of total recorded cost.
Amounts are in USD. No currency conversion is performed.
How it works
Enter the original share quantity, original cost per share in USD, and a split ratio. The ratio can use a colon or slash, such as 2:1 or 1/10. A single number such as 3 is read as 3:1. Empty or malformed ratios do not produce a result.
The calculator multiplies shares by the ratio and divides unit cost by the same ratio. It also shows total recorded cost before and after the adjustment as a mathematical check. Shares and unit cost may be zero; each ratio part must be positive.
Use the same purchase lot and currency on both sides of the calculation. Fractional shares are kept as calculated. Brokers can apply different rules for fractional entitlements, cash in lieu, fees, and lot reporting.
The split ratio is the only value saved in local browser storage when available. Share count and unit cost remain in the current page session and are not saved.
Step by step
- Enter the original share quantity and unit cost in USD.
- Enter the full positive split ratio.
- Compare the resulting shares and unit cost with the unchanged total cost.
Worked examples
For a 2:1 split, 100 shares at a USD 40 unit cost become 200 shares at USD 20 per share. Total recorded cost remains USD 4,000. For a 1:10 reverse split, the same starting position becomes 10 shares at USD 400 per share, also totaling USD 4,000.
The calculations use fractional share quantities when the ratio requires them. A broker may apply its own fractional share, cash in lieu, fee, or account handling rules.
When to use this calculator
Use the calculator to check how a stated split ratio changes the share count and cost per share for one entered lot.
Compare the arithmetic with the issuer’s corporate action details and your broker statement. The result does not replace either record.
Common mistakes
Enter the ratio in the direction the shares change. A 2:1 split doubles shares, while a 1:2 split halves them. Reversing the ratio reverses both output adjustments.
Do not use a market price as the original purchase cost unless that is the cost per share for the lot being modeled. The tool does not fetch prices or confirm the date and basis of your records.
Formula
ratio = numerator / denominator
new shares = old shares × ratio
new cost per share = old cost per share / ratio
old total cost = old shares × old cost per share
adjusted total cost = new shares × new cost per share
The calculation preserves total recorded purchase cost within numeric precision. It models fractional shares and does not round to a broker’s whole share policy. It does not establish market value, tax basis, fees, or cash in lieu.
Assumptions and limits
This is split arithmetic, not a quote, price forecast, broker record, or tax basis determination. It assumes the entered quantity and per share cost refer to the same lot, date convention, currency, and unit basis. It models fractional shares and does not model cash in lieu, broker rounding, fees, taxes, dividends, or other corporate actions. All money values are displayed in USD without conversion.
Key terms
- Split ratio
- A corporate action ratio that changes the share quantity and cost per share proportionally.
- Original cost per share
- The entered purchase cost for one share before applying the split ratio.
- Total recorded cost
- The entered share quantity multiplied by the entered cost per share. The split arithmetic keeps this total unchanged within numeric precision.
Related calculations
Use this calculation to check the mechanical share and per share cost changes from a split. Other portfolio tools can answer questions about separate purchases, returns, or tax rules.
This result does not use a market quote or confirm a tax lot. Review the issuer’s split terms and your account records separately.
FAQ
What does a stock split adjustment calculate?
A split changes the number of shares and the corresponding cost per share by a stated ratio. This calculator applies that ratio to the quantity and unit cost you enter. It does not establish the market value or tax basis reported by your broker.
How does the ratio change shares and unit cost?
For a 2:1 split, each old share becomes two shares and the cost per share is halved. For a 1:10 reverse split, ten old shares become one new share and the cost per share is multiplied by ten. The total recorded purchase cost is unchanged by this arithmetic.
What is the difference between a forward and reverse split?
A forward split has a ratio above one, such as 3:1, and increases the share count. A reverse split has a ratio below one, such as 1:4, and decreases it. The direction alone does not establish how the company or investment will perform.
Which split ratio formats are accepted?
Enter a positive ratio as numerator:denominator or numerator/denominator. A single positive number such as 3 means 3:1. The parser requires the entire entry to be a valid finite positive ratio. It does not turn blank or malformed text into 1:1.
Does this confirm my tax basis after a split?
The arithmetic can help you compare records before and after a split, but it does not verify the broker’s posted basis or determine tax treatment. Check the corporate action details and account statement for the applicable lot information.
Related tools
Use related calculations for questions about multiple purchases, holding periods, or portfolio returns. Those calculations use different inputs and do not verify this split’s broker or tax treatment.