Stock Split Calculator
Calculate your shares, adjusted price, and per-share cost basis after a forward or reverse stock split. Use any A-for-B ratio or choose a common example.
Shares after split
200
2-for-1 forward split — share count doubles and price per share halves
- Split type
- Forward split
- New-for-old ratio
- 2-for-1
- Adjusted price per share
- $50.00
- Adjusted cost basis per share
- $40.00
- Holding value before
- $10,000.00
- Theoretical value after
- $10,000.00
- Change in share count
- +100.00%
- Change in price per share
- −50.00%
- Fractional-share result
- No fractional share
Your values in the formula
Shares:
100 × 2 ÷ 1 = 200 shares
Price / per-share basis:
$100.00 × 1 ÷ 2 = $50.00 per share
Value check:
100 × $100.00 = 200 × $50.00 = $10,000.00
Check the formula and official examples. The adjusted price is a proportional reference, not a prediction. Check the issuer notice or your broker for fractional-share treatment.
Combine the adjusted position with later purchases
A split changes the number of shares and the per-share basis, not the total basis in this arithmetic.
Carry the post-split shares and adjusted per-share basis into the Stock Average Calculator as one purchase lot, then add any later buys.
Use adjusted position in Stock Average CalculatorHow to calculate a stock split
Read the ratio as new-for-old
In a 3-for-2 split, every two old shares become three new shares. In a 1-for-20 reverse split, every 20 old shares become one new share.
Multiply shares by the ratio
Post-split shares equal old shares multiplied by the new-share part and divided by the old-share part.
Apply the reciprocal to price and basis
The adjusted per-share price and cost basis multiply by the old-share part and divide by the new-share part.
Verify the total and check the notice
Before rounding or cash-in-lieu, shares times price reconcile to the same theoretical value. Actual fractional treatment comes from the issuer and broker.
Stock split formula
This calculator uses one convention for every split: A-for-B means A new shares replace B old shares. The share multiplier is A ÷ B; the per-share price and basis multiplier is B ÷ A.
New shares = old shares × new-ratio part ÷ old-ratio part
Adjusted price or basis = old price or basis × old-ratio part ÷ new-ratio part
Old shares × old price = new shares × adjusted price (before market movement and fractional treatment)
Forward stock splits: 2-for-1, 3-for-2, 3-for-1, and more
A forward split has a larger first number than second number. A 2-for-1 split doubles shares and halves the per-share figure. A 3-for-2 split multiplies shares by 1.5 and the per-share figure by two-thirds. A 3-for-1 split triples shares and divides the per-share figure by three. The same rule covers 4-for-1, 5-for-1, and 5-for-4 splits.
Reverse stock splits: 1-for-10, 1-for-20, 1-for-30, and 1-for-100
A reverse split has a smaller first number than second number. A 1-for-10 reverse split combines every ten old shares into one new share and multiplies the per-share figure by ten. A 1-for-20 multiplies it by 20; a 1-for-30 by 30; a 1-for-100 by 100. FINRA's example uses a 1-for-200 economic ratio: 5,000 shares at $0.10 become 25 shares at $20 before fractional treatment.
Why ratio notation can look backwards
Some announcements say “200:1 reverse split” while describing one new share for every 200 old shares. To remove that ambiguity, this page labels the boxes explicitly and always displays the economic result as new shares for old shares: 1-for-200.
How a split changes cost basis per share
For a proportional split, the total cost basis is allocated across the new number of shares. If 100 shares have a $50 per-share basis, total basis is $5,000. After a 2-for-1 split, 200 shares have a $25 basis each. This arithmetic does not determine tax reporting for cash paid instead of a fractional share.
Fractional shares, rounding, and cash in lieu
The calculator keeps the exact theoretical result. Actual terms vary: an issuer may permit fractions, round them, aggregate and sell them, or pay cash in lieu. Investor.gov notes that some reverse splits cash out small shareholders. Read the issuer filing and ask your broker before treating the displayed fraction as the settled position.
What the calculator does not predict
A split itself changes the unit count, not the business. The proportional price is only a split-adjusted reference. Trading can move the market price immediately, and this page does not predict performance, liquidity, taxes, fees, listing outcomes, dividends, spin-offs, mergers, or option-contract adjustments.
Forward and reverse stock split examples
These examples cover the ratio phrases people most often search. The first three are checked against Investor.gov or FINRA.
- 2-for-1 stock split calculator example. Investor.gov's 100 shares at $100 become 200 shares at $50. The theoretical holding value stays $10,000.
- 3-for-2 stock split. FINRA's 10 shares at $100 become 15 shares at about $66.67. Using the unrounded price, the theoretical value stays $1,000.
- 1-for-200 reverse stock split. FINRA's 5,000 shares at $0.10 become 25 shares at $20. The theoretical value stays $500.
- 3-for-1 forward split. 40 shares at $90 become 120 shares at $30. A $90 per-share cost basis likewise adjusts to $30.
- 1-for-10 reverse split. 1,000 shares at $2 become 100 shares at $20 before any fractional treatment.
- 1-for-20 reverse split with a fraction. 55 shares at $0.50 produce a theoretical 2.75 shares at $10. The issuer or broker decides whether the 0.75 share remains, is rounded, or is paid in cash.
Checked against official stock split examples
The default and two presets reproduce examples published for investors by Investor.gov and FINRA:
- Investor.gov 2-for-1: 100 shares × 2 ÷ 1 = 200 shares; $100 × 1 ÷ 2 = $50.
- FINRA 3-for-2: 10 shares × 3 ÷ 2 = 15 shares; $100 × 2 ÷ 3 = $66.666… before display rounding.
- FINRA reverse split: 5,000 shares × 1 ÷ 200 = 25 shares; $0.10 × 200 ÷ 1 = $20.
- Value reconciliation: the exact arithmetic preserves $10,000, $1,000, and $500 respectively before market movement or fractional-share terms.
Investor.gov — Stock Split — the SEC investor-education definition and 2-for-1 worked example.
FINRA — Stock Splits — the forward, 3-for-2, and 1-for-200 reverse-split worked examples.
Checked 3 August 2026. Investor.gov, the SEC, and FINRA have not reviewed or endorsed CalcStocks. Their examples verify the arithmetic, not whether any split or security is a good investment.
Stock split calculator questions
Formulas, common ratios, reverse splits, cost basis, fractional shares, and what the result cannot tell you.
Formula
How do I calculate a stock split?
Treat the ratio as new shares for old shares. Multiply current shares by the first number and divide by the second. Multiply the pre-split price or per-share basis by the second number and divide by the first.
What is the stock split formula?
For an A-for-B split: post-split shares = pre-split shares × A ÷ B. Adjusted price or per-share basis = pre-split amount × B ÷ A.
Why is the theoretical investment value unchanged?
The share multiplier and price multiplier are reciprocals. Multiplying one factor by A ÷ B and the other by B ÷ A cancels out, before market movement, rounding, or cash paid for a fraction.
How does the calculator know whether a split is forward or reverse?
If the new-share part is larger than the old-share part, it is forward. If it is smaller, it is reverse. Equal numbers produce no economic change and are labeled no change.
Is the adjusted share price a prediction?
No. It is the proportional reference price implied by the ratio at the split moment. Trading, news, supply, demand, and other facts can move the actual market price.
Common ratios
How does a 2-for-1 stock split work?
Every one old share becomes two new shares. Share count doubles, while the proportional price and per-share basis are divided by two. Investor.gov gives 100 shares at $100 becoming 200 at $50.
How do I calculate a 3-for-2 stock split?
Multiply shares by 3 ÷ 2, or 1.5. Multiply the price and basis by 2 ÷ 3. FINRA gives 10 shares at $100 becoming 15 shares at about $66.67.
What happens in a 3-for-1 stock split?
Each old share becomes three new shares. Share count triples and the proportional price and per-share basis become one-third of their pre-split amount.
What happens in a 5-for-4 stock split?
Multiply shares by 5 ÷ 4, or 1.25, and multiply the per-share figure by 4 ÷ 5, or 0.8. A holding that is not divisible by four may produce a theoretical fraction.
Can I calculate a 4-for-1 or 5-for-1 split?
Yes. Enter 4 and 1, or 5 and 1. The same A-for-B formula works for any positive whole-number ratio within the input limits.
Why do some sites write split ratios in the opposite order?
Announcements and informal descriptions are not always consistent, especially for reverse splits. This calculator always means new shares for old shares and labels both fields so the economic conversion is explicit.
Reverse splits
How do I calculate a reverse stock split?
Enter the smaller new-share number first and the larger old-share number second. For a 1-for-10 reverse split, divide shares by 10 and multiply the price and per-share basis by 10.
What is a 1-for-10 reverse stock split?
Every ten old shares combine into one new share. A 1,000-share holding becomes 100 theoretical shares, and a $2 per-share figure adjusts to $20 before market movement.
What is a 1-for-20 reverse stock split?
Every 20 old shares combine into one new share. Divide the share count by 20 and multiply the per-share price or basis by 20.
How do I use a 1-for-30 reverse stock split calculator?
Set new shares to 1 and old shares to 30. A 3,000-share position becomes 100 theoretical shares; a $0.40 price adjusts proportionally to $12.
What does a 1-for-100 reverse stock split do?
It combines each 100 old shares into one new share and multiplies the proportional per-share figure by 100. Actual fractional and round-lot treatment must be checked in the issuer notice.
Is a reverse stock split good or bad?
The ratio arithmetic cannot answer that. FINRA warns that reverse splits often involve low-priced, higher-risk stocks, while the split itself does not change company value. Assess the company and filing separately.
Basis and limits
How does a stock split affect cost basis per share?
The total basis is allocated across the post-split shares in this proportional arithmetic. Multiply the old per-share basis by old-ratio part ÷ new-ratio part. Keep your broker's official records for tax reporting.
What happens if a reverse split creates a fractional share?
Terms vary. The issuer or broker may keep a fraction, round it, aggregate and sell fractions, or pay cash in lieu. Investor.gov notes that some reverse splits cash out small shareholders.
Does the calculator determine taxes on a stock split?
No. It shows proportional share and basis arithmetic only. Cash in lieu, jurisdiction, account type, and issuer terms can affect reporting, so use official tax records or professional advice.
Is a stock split the same as a stock dividend?
No. They can produce similar share-count changes, but legal, accounting, dividend, and tax treatment can differ. This page handles only an announced A-for-B stock split ratio.
Does this adjust options contracts after a split?
No. Option deliverables, strikes, and multipliers can be adjusted under contract-specific rules. Use the official Options Clearing Corporation memo or your broker for that contract.
Is the stock split result investment advice?
No. It is transparent arithmetic from numbers you enter. It does not evaluate the company, forecast the post-split price, or recommend buying, selling, or holding a security.
Other stock position tools
Use adjusted shares and basis in the average-cost tool, or calculate profit and ownership dilution with the same browser-only approach.
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Share Dilution Calculator
Calculate how a new stock issuance changes shares outstanding and existing ownership. Add your holding to see before, after, and pro-rata figures.
Method, primary sources, and limitations
Built and maintained by CalcStocks as a browser-only stock-position calculator. The method is displayed in full and tested against official investor-education examples.
- Investor.gov — Stock Split — defines a stock split, distinguishes it from issuing dilutive new shares, and gives the 100-at-$100 to 200-at-$50 example.
- Investor.gov — Reverse Stock Splits — explains one-for-ten conversion, cashing out of some small holders, filings, and the limits of what the split itself says.
- FINRA — Stock Splits — publishes 2-for-1, 3-for-2, and reverse-split examples and explains that splitting shares does not itself change company value.
- Investor.gov — Fractional Share Investing — explains that broker handling of fractions and corporate actions can differ and should be confirmed with the firm.
The result is theoretical proportional arithmetic from visitor-entered numbers. It does not fetch a ticker or notice, predict the trading price, determine cash in lieu or rounding, model taxes or fees, or adjust dividends, spin-offs, mergers, warrants, or options. Verify the announced ratio and settlement terms in the issuer filing and with your broker. Nothing here is investment, tax, accounting, or legal advice.