Bonus Issue, Stock Split & Reverse Split Calculator

What to check when an ex-rights adjustment lowers the price

A large drop in the displayed share price after a bonus issue can look like a loss of invested capital.
First reconcile the change in share count, the entitlement to new shares and their account-credit date.
This calculator puts bonus issues, stock dividends, stock splits and reverse splits into a worksheet for checking a disclosure against your holdings.

An adjusted base price and a market execution price serve different purposes.
The base resets the price reference for the corporate action; supply and demand still determine actual trades.
An increase in share count alone does not establish an investment gain.
Compare the price change together with the shares you are entitled to receive.

How the four corporate actions differ

Transfer the right inputs from the disclosure

• Eligible existing shares: use the quantity entitled at the specified record date, rather than assuming that today’s visible balance qualifies.
  For multiple accounts, first check whether fractional entitlements are settled separately, then calculate each account where appropriate.
  
• Existing average cost: use the pre-action purchase average.
  Keep treatment of acquisition fees and other costs consistent when comparing profit figures.
  
• Cum-rights or pre-action final close: entering an already adjusted price applies the adjustment twice.
  For a bonus issue, use the close before the ex-date; for a split or consolidation, use the final pre-change trading close.
  
• Personal allocation versus price ratio: treasury-share exclusions can make personal allocation differ from new shares divided by pre-issue total shares.
  The default assumes equality.
  Use the separate price ratio when the disclosed figures differ.
  
• Fraction price: do not automatically use par value or your acquisition price.
  Follow the disclosed sale or settlement method, such as the first listing-day close.
  Keep the status unknown while the relevant price remains undetermined.
  
• Disclosed base and scenario price: the exchange-announced base is a comparison with theory; the valuation price is your own post-listing scenario.
  They do not need to be the same number.
  

Share allocation and theoretical ex-rights formulas

Theory is an unadjusted mathematical reference.
An actual exchange announcement may apply tick-size handling or a security-specific measure.
Entering the disclosed base shows the difference from theory; that difference is not automatically an error or a trading profit.

Last eligible purchase and ex-date: T+2 and closures

Ordinary Korean share transactions settle on T+2, two trading and settlement days after the trade date.
A purchase must settle by the relevant record date for ordinary record-date entitlement.
The calculator finds the last settlement day on or before the record date, then moves back two trading days for the last eligible buy date.
The indicative ex-rights or ex-dividend date is the trading day after that purchase cutoff.

The 2026 calendar excludes weekends, public and substitute holidays, Labor Day, the local election day, July 17 and the December 31 year-end closure.
Add any emergency closure dates explicitly.
Automatic dates are withheld when the calculation leaves the supported year.
Unconfirmed terms or calendar checks leave dates tentative; only confirmed reminders are exported.

Splits and reverse splits involve suspension and relisting procedures, so this tool does not assign the ordinary bonus-issue ex-date to them.
For a bonus issue, a disclosed halt overlapping the purchase-cutoff-to-record-date window also withholds ordinary T+2 dates.
Confirm the final tradable date, execution and settlement with the broker before acting.

Worked bonus example: 333 shares and a 15% allocation

Assume 333 shares, average cost KRW 20,000, previous close KRW 23,000 and equal personal / price ratios of 0.15.
The new-share entitlement is 49.95: 49 additional whole shares and a 0.95 fraction.
Final credited whole shares are 382, and theoretical base = 23,000 ÷ 1.15 = KRW 20,000.

If the fraction price is unknown, the calculator does not establish a KRW 17,100 payment.
It still shows the whole-share value but withholds the cash-inclusive total and profit.
Assumed and confirmed fraction prices have separate labels.
The approximately 20.7072% return in this example comes from the assumed valuation price and fractional payment, not from the bonus issue itself.

Split and reverse-split examples, and the two averages

The fraction-inclusive average divides the old average by the share-count multiplier.
The whole-share average allocates all original purchase cost to the whole shares actually credited.
The latter does not allocate a separate cost basis to fractional entitlements, so it must not be copied directly into a broker ledger or tax return.
It is withheld when no whole shares remain.

Tradable shares before listing and how to read profit

A right to receive bonus or dividend shares and a credited tradable balance can arise at different times.
For a supported valuation date after the record date but before listing, confirmed open trading gives the existing share count as an indicative tradable quantity.
From listing onward, it gives the final whole-share count.
A confirmed halt, a disclosed halt interval or a market-closed valuation day gives zero.
Unknown trading status or required dates withhold the quantity.

Collateral, stock lending, settlement, lockups and broker account-credit processing can also restrict actual orders.
The displayed quantity does not establish permission to sell uncredited shares or open a short position.
For splits and reverse splits, pre-relisting tradability is withheld rather than assumed equivalent to ordinary existing-share trading.

From disclosure review to account reconciliation

1. Identify the action and eligible share class in the latest amended disclosure.
   Separate paid and bonus stages when their record dates differ.
   
2. Transfer eligible holdings, old average, pre-action close and ratios.
   Check the old-to-new direction for splits and consolidations.
   
3. Keep unknown, assumed and confirmed fraction prices and disclosed bases distinct.
   Record the evidence check date when selecting a confirmed status.
   
4. Reconcile the record date, listing date, halt period and any additional closures.
   Read why a date is adjusted or withheld and prepare questions for your broker.
   
5. Save the TXT worksheet or print it to compare actual whole-share credits and fraction cash.
   Confirmed dates can be saved as anonymous all-day ICS reminders without your account quantity in their titles.
   

For a planned sale to fund living expenses, separate dates before and after listing rather than relying on the total future share count.
For a small holding facing consolidation, pay particular attention to receiving only a fraction and to the actual cash-payment date.
Reconcile family members’ accounts independently where settlement is performed per account.

Scope and input cautions

A statutory basis for fractional settlement does not establish one universal payment price or date.
Actual disclosures and account statements govern rounding below KRW 1, tax, payment timing and settlement amounts.
The calculator does not automatically compute deemed-dividend taxation arising from the bonus issue’s reserve source or tax on stock dividends.

Numeric fields accept commas and the stated decimal precision.
Negative or out-of-range amounts, impossible dates and ratios in the wrong direction are rejected.
Changing inputs hides the old result until you calculate again.
Marking a value confirmed does not replace reviewing the actual disclosure.

Frequently asked questions