How many shares will you hold after a stock split, and what should the adjusted price be? Enter the split ratio as new shares : old shares, the shares you hold before the split and a reference price. The result is theoretical: your issuer and broker decide how any fractional share is actually handled.
A split alone does not create profit. Before fractional-share treatment or market movement, the theoretical total value of the holding stays the same.
Stock split calculator
This calculator runs in your browser. This calculator’s code does not send, save, or track your entries. All dollar amounts are USD.
Optional example: Inputs start blank. Load example fills hypothetical figures without calculating. Examples are not current rates, quotes, or recommendations.
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How do you enter a split ratio in the stock split calculator?
Use the two separate whole-number fields, not a percentage or a decimal multiplier. For a 3-for-2 forward split, enter 3 new shares and 2 old shares. For a 1-for-10 reverse split, enter 1 new share and 10 old shares.
Read the issuer’s announcement carefully and map its wording to new : old before you type. This calculator always reads the first field as new shares and the second as old shares.
Enter the shares held before the split, including any existing fractional quantity, and a pre-split price assumption. The price is not your purchase cost, a live quote or a prediction.
For an optional basis illustration, select Yes and enter the total modeled basis for the whole holding, not a per-share amount. Otherwise leave the feature off and enter 0 in the basis field.
What does a split change, and what stays the same?
| Measure | Forward split | Reverse split |
|---|---|---|
| New : old ratio | New term is larger, such as 3:2 | New term is smaller, such as 1:10 |
| Theoretical shares | Increase | Decrease |
| Theoretical price per share | Decreases proportionately | Increases proportionately |
| Theoretical total value | Unchanged | Unchanged |
| Fractional result | Shown in this model, not confirmed as deliverable | Shown in this model, not confirmed as deliverable |
| Future trading performance | Not predicted | Not predicted |
SEC’s Investor.gov stock-split definition describes an increase in share count without a change in shareholders’ equity. Its example: 100 shares at $100 become 200 shares at $50 after a two-for-one split.
FINRA’s stock-split guide says the most common forward splits are 2-for-1, 3-for-2 and 3-for-1, and that the total value of the shares is the same right after the split. Neither source says the traded price will stay at the theoretical adjusted amount.
How does a hypothetical 3-for-2 split work with 101 shares?
Inputs. 101 shares, a hypothetical $90 reference price and a 3 : 2 ratio. The modeled holding is 101 × $90 = $9,090.
Formula. New shares = 101 × 3 ÷ 2. Adjusted price = $90 × 2 ÷ 3.
Result. You get 151.5 theoretical shares at $60 per share. Multiplying 151.5 by $60 still gives $9,090.
What to check. The extra 50.5 shares are not a $3,030 profit; the same holding is divided into smaller units. The 0.5-share portion is shown, not discarded or converted to cash. Check how the issuer and your broker will handle it before treating 151.5 as your final quantity.
With the optional illustration on and a total modeled basis of $6,060, the total stays $6,060. The simple per-share figure changes from $60 before the split to $40 afterward.
How does a hypothetical 1-for-10 reverse split work?
Inputs. 25.5 shares at a hypothetical $4 each, worth $102, and a 1 : 10 ratio.
Formula and result. 25.5 × 1 ÷ 10 = 2.55 theoretical shares. The adjusted price is $4 × 10 ÷ 1 = $40. The theoretical total is still 2.55 × $40 = $102, not a tenfold gain.
What to check. The calculator does not round 2.55 down to 2 or assume payment for the remaining 0.55 share. With an optional total modeled basis of $76.50, the total stays $76.50 and the simple basis per new share is $30, versus $3 before.
Investor.gov’s reverse-split explanation notes that in some reverse splits small shareholders are cashed out, receiving cash in lieu of partial shares. That is a possibility, not a default treatment applied here.
What happens to your cost basis after a split?
IRS Publication 550 says you must reduce the basis of your original stock when you receive more shares from a stock split. When the new and old stock are identical, you divide the adjusted basis of the old stock by the total number of old and new shares.
That is the same total-holding division the optional illustration uses. It is still a simplified view: it does not allocate basis across several purchase lots, and it does not calculate tax on any cash paid for a fractional share. Compare the result with your broker’s adjusted cost-basis records.
How the calculator handles inputs and rounding
Let Q be original shares, P the pre-split reference price, N the new-share term and D the old-share term.
- Theoretical new shares = Q × N ÷ D
- Theoretical adjusted price = P × D ÷ N
- Original value = Q × P, reused after the split because the ratio factors cancel
- Optional basis per new share = total modeled basis ÷ theoretical new shares
The original total is rounded half up to cents once and reused before and after the split, so rounding cannot suggest a gain or loss. For example, 100.02 shares × $1.25 = $125.025, displayed as $125.03 on both sides. Total modeled basis uses the same half-up cents rule.
Share quantities, adjusted prices and per-share basis keep unrounded values, shown to up to eight decimal places or in scientific notation when very small (1e-12 means 0.000000000001). For example, $100 adjusted by 2 ÷ 3 is about $66.666667, not exactly $66.67. None of these display rules is an issuer rounding instruction.
Ratio terms must be whole numbers from 1 to 1,000,000. Original shares can be zero or from 0.000001 up to 1 billion, and the reference price zero or from $0.000001 up to $1 million. Total modeled basis is limited to $1 trillion. Equal ratio terms show no change, and zero shares mark per-share basis as undefined.
When does a split calculation not fit your records?
- The company pays cash for fractional shares. The tool keeps the fraction and does not model cash in lieu or its tax treatment.
- You bought the shares in several lots. Basis is divided across the whole holding, not allocated lot by lot.
- You plan to move the account. FINRA notes that fractional shares currently can’t be transferred to another brokerage firm, so they may have to be sold first, possibly with taxes and fees.
- You want to know what happens next. The model covers one split, not later trading, dividends, purchases, sales, fees or taxes.
For income from holding the shares, use the separate stock dividend calculator. To measure the result of buying and later selling, the stock profit calculator compares purchase cost with sale proceeds after fees. A split by itself has neither a sale nor a profit.
Quick decision checklist
- Read the issuer’s announcement for the exact ratio, effective date and fractional-share terms.
- Enter the ratio as new shares first and old shares second.
- Ask your broker how any fraction will be delivered or paid, and when the adjusted position appears.
- Compare your new share count and adjusted basis with the broker’s corporate-action entries.
- Do not treat the theoretical adjusted price as an execution price.
Sources and editorial disclosure
- SEC Investor.gov: Stock Split, share count rises without a change in shareholders’ equity.
- FINRA: Stock Splits, common ratios, offsetting price adjustment and reverse splits.
- SEC Investor.gov: Reverse Stock Splits, conversion into fewer shares and possible cash in lieu of partial shares.
- FINRA: Investing in Fractional Shares, broker handling and limited transferability.
- IRS Publication 550, Investment Income and Expenses, reducing and dividing stock basis after splits.
Sources checked September 28, 2026. They support general split mechanics and cautions, not a particular issuer’s terms or a verified tax outcome. The examples and numerical limits are this calculator’s own hypothetical modeling choices.
Prepared with AI-assisted research, drafting, and calculation checks. Not independently reviewed by a human financial professional.
