Stock split & reverse split calculator
A split changes how many shares you hold and the price of each one — but not your total cost basis and not the value of your position. Enter your holding and the split ratio to see your new share count and adjusted per-share basis, with any fractional share that might be paid as cash-in-lieu.
Do I lose or gain money in a split?
No — a stock split is cosmetic. It’s the equity equivalent of changing a $20 bill into two $10s: you have more pieces of paper, each worth less, and the total in your wallet is identical. A forward split (say 4-for-1) gives you more shares at a proportionally lower price; a reverse split (say 1-for-10) does the opposite — fewer shares at a proportionally higher price. In both, the moment the split takes effect your position is worth exactly what it was worth the instant before. Companies split to move the share price into a more convenient range — forward splits after a big run-up, reverse splits to lift a low price back above an exchange’s minimum listing threshold. Neither creates or destroys value.
new shares = old shares × (new ÷ old) · new price = old price × (old ÷ new)
Does a split change my cost basis?
Your total cost basis is unchanged — you spent what you spent, and a split doesn’t touch that. What changes is your per-share cost basis, because the same total is now divided among a different number of shares. Bought 100 shares for $5,000 (a $50 basis each) and the stock does a 4-for-1 split? You now hold 400 shares, your total basis is still $5,000, and your per-share basis is $12.50. This matters when you eventually sell: your gain is still measured against that unchanged $5,000 total, just spread across more (or fewer) shares. If you want to work out the gain on a later sale, hand the adjusted figures to the cost-basis calculator — a distinct job that decides which lots are sold and what you report.
Fractional shares: odd ratios (like 3-for-2) and most reverse splits can leave you with a fraction of a share. Your broker either credits that fraction to your account or pays cash-in-lieu — the market value of the fraction — which is a small taxable sale. The calculator above shows the fractional part so you know what to expect.
Illustrative math on the numbers you enter, not tax advice. Cash-in-lieu and lot-level basis on a later sale can affect what you actually report — confirm with your broker’s statements. Educational tool, not financial advice. Your figures never leave the page — the calculation runs entirely in your browser. The page loads standard pageview analytics, which never sees your numbers.
This math stops at what you typed in.
Tradune runs it continuously on your real holdings — with your money-weighted return next to a buy-and-hold SPY twin, and SEC insider filings flagged on the stocks you own.
Educational analytics — not investment advice.