How to Calculate a Stock Split or Reverse Stock Split

What changes when a stock splits

A stock split changes the units in which a holding is expressed. A forward split increases the number of units, while a consolidation combines existing units into fewer shares. In either case, the reference price moves in the reciprocal direction in the theoretical calculation.

This guide shows how to read the ratio, calculate the shares and price, and separate a theoretical fraction from the eventual account credit.

Read new-for-old terms

Q is the pre-split holding and P is its pre-split reference price per share. N-for-O means N new shares for every O old shares. N greater than O is a forward split. N below O is a reverse split or consolidation. Equal terms describe an identity conversion.

An announcement may describe the exchange in words rather than using a colon. Convert it to new shares for old shares before entering it. For example, one new share for ten existing shares is 1-for-10.

Check a position before consulting settlement terms

Use the model to understand a split notice, compare equivalent ratios, or reconcile why a change in share count need not change immediate modeled value. Keep the price and share count on the same pre-split basis.

Shares and price adjust by reciprocal factors

Multiply Q by N/O for theoretical shares and multiply P by O/N for theoretical reference price. The reciprocal factors cancel in the unrounded product. The modeled position value is Q × P on either side. Divide the exact share numerator by its denominator to identify the whole component and fractional remainder.

New shares = Q × N / O

Verified forward and reverse examples

A 1-for-10 reverse split turns 103 shares at a pre-split reference price of 2.40 into 10.3 theoretical shares at 24 per share. The exact decomposition is 10 whole shares plus 3/10 of one share. The modeled value is 247.20 on either side before market movement or settlement. A 3-for-2 forward split turns 5 shares at 90 into 7.5 theoretical shares at 60, preserving 450.

With two shares in a 1-for-3 consolidation, the exact output is 2/3 of a share. The decimal repeats and the whole component is zero. Neither statement determines what the broker will credit.

1. Identify the new-for-old terms as 1 and 10.
2. Multiply 103 by 1/10 to obtain 10.3 theoretical shares.
3. Multiply 2.40 by 10/1 to obtain a reference price of 24.
4. Reconcile both unrounded modeled values to 247.20.

Enter the holding and reference quote

Read the issuer notice to identify how many new shares replace the specified old shares. Enter the holding and a pre-split reference price in one major currency. Enter the two ratio terms separately and compare the decimal estimate with the exact whole and fractional components.

If the original price is already split-adjusted, do not adjust it again. Enter zero explicitly when it is the intended quantity or reference value.

Separate the exact fraction from delivery

The fraction is a mathematical entitlement before settlement. It does not indicate the number of shares credited or a cash amount. The theoretical reference price is a unit adjustment to the supplied quote. The market can trade at a different price.

A share count just below a whole number can look whole when rounded to a short decimal. Check the exact whole and fraction outputs before comparing with a statement. The fraction by itself does not supply a cash settlement price.

Reference price, purchase cost and shareholder return

A reference price describes the price basis you supplied. A purchase cost records a transaction, and a tax basis follows applicable records and rules. Use the Stock Average Price guide for weighted purchase costs.

A split conversion is not an investment return. The Total Shareholder Return guide compares a period of price and dividend outcomes. Keep all historical prices and shares on a consistent basis when making that comparison.

What remains constant in the model

One security, consistent share units and one ratio. The model isolates the split before settlement and market movement. It does not reuse a price series that has already adjusted for the same split or infer a ratio from a face-value quote.

Applying the reciprocal split to the exact outputs would recover the opening shares and price. Actual fractional settlement or price movement can make the same exercise on a broker statement differ.

Supported bounds and rounding

Shares and price accept explicit zero and values through 1e12, with 12 fractional places and 48 characters. Each ratio term is a positive whole number no greater than 1,000,000. Exact integer arithmetic preserves the remainder and modeled value. Decimal presentation starts from 80 significant digits and displays shares and price with up to 12 significant figures. Money is displayed to cents with a marker for tiny nonzero amounts.

Exact input bounds imply theoretical shares and price through 1e18 and modeled value through 1e24. A repeating share fraction is shown as a reduced rational number, so it remains visible even when a rounded decimal conceals it.

Common notation and price errors

Check ratio direction, share units and quote currency. An issuer notice might state the old and new terms in a different order from the form. Do not confuse face value, purchase cost and reference price. Do not multiply rounded displayed values to reconcile exact modeled value.

If a reverse split appears to multiply the share count, check whether old and new terms were swapped. Compare the implied share multiplier with the wording in the original notice.

Reading notices across five markets

The USA, UK, Canada, Australia and India choices format USD, GBP, CAD, AUD and INR. UK quotes can be expressed in pence, while India notices may describe a face-value subdivision. Enter the actual pre-split reference price in major currency units.

The cited LSE, ASX and NSE notices show event-specific handling of fractions. The TSX source describes security split notices. These sources illustrate why the issuer terms matter for actual settlement.

Educational scope

Educational theoretical conversion before market movement and settlement. Excludes cash-in-lieu, delivered shares, broker rounding, live prices, tax basis, fees, FX, effective dates and eligibility. No personalized investment advice.

The calculator explains the mechanics of one supplied split ratio. Check issuer materials and account records to confirm your particular event.

Frequently asked questions

Sources and review

Sources reviewed Nov 7, 2026. Consult current local rules before relying on time-sensitive information.

• Investor.gov: stock splits
• Investor.gov: reverse stock splits
• LSE: issuer consolidation notice
• TSX: security split notices
• ASX: issuer consolidation example
• NSE: issuer subdivision notice