How the split is worked out
Every buy is costed on its own, the buys are pooled into one share count and one average cost, and then the ratio is applied to all of it at once. Nothing about the money changes — only the share count and everything measured per share.
- Cost of a buy = shares bought × price per share
- Money paid in = cost1 + cost2 + … (unchanged by the split)
- Shares before = shares1 + shares2 + …
- Average cost before = money paid in ÷ shares before
- Ratio = New ÷ Old
- Shares after = shares before × ratio
- Average cost after = money paid in ÷ shares after
- Cost basis per share after = money paid in ÷ shares before ÷ ratio
- Market value after = shares after × price after the split
- Profit / loss = market value after − money paid in
- Cash in lieu = the fractional part of the share count × price after the split
Shares after = shares before × (New ÷ Old) and cost per share after = cost per share before ÷ (New ÷ Old)
Worked example, forward: 100 shares at 50.00 and 50 shares at 60.00. Money paid in is 5,000.00 + 3,000.00 = 8,000.00 for 150.0000 shares, so the average cost before is 8,000.00 ÷ 150.0000 = 53.3333. A 2-for-1 split is New 2, Old 1 — a ratio of 2. Shares after are 150.0000 × 2 = 300.0000 (200.0000 from the first buy, 100.0000 from the second), the average cost after is 8,000.00 ÷ 300.0000 = 26.6666, and each buy's own cost per share halves with it: 25.0000 and 30.0000. At a price of 30.00 after the split the position is worth 300.0000 × 30.00 = 9,000.00, a profit of 1,000.00 on the 8,000.00 paid in, a return of 12.50%. The money paid in reads 8,000.00 before and 8,000.00 after, because a split does not put money in or take it out.
Worked example, reverse: 15 shares at 100.00 is 1,500.00 paid in. A 1-for-10 reverse split is New 1, Old 10 — a ratio of 0.1. Shares after are 15.0000 × 0.1 = 1.5000 and the cost per share becomes 1,500.00 ÷ 1.5000 = 1,000.0000. At 1,100.00 after the split the position is worth 1.5000 × 1,100.00 = 1,650.00. If your broker only holds whole shares, you keep 1 share and the remaining 0.5000 is paid out in cash at that price: 0.5000 × 1,100.00 = 550.00.
Rounding: every figure on this page is rounded down, never up — the same rule as the rest of the site. Share counts and per-share figures are shown to four decimals, amounts and percentages to two, so the number you read is never larger than the one that was computed. Shares after the split is the sum of the per-buy figures printed beside each row, so the column and the total agree with each other.
Why the page asks for every buy
Most split calculators answer one question only: how many shares will I have. That is the easy half. The half that is harder to do in your head is what the split does to the price you paid — and if you bought in several goes at several prices, there is no single purchase price to divide, only an average of them.
So this page carries the buys through the split with you. Each buy keeps its own money, gets its own new share count and its own cost per share, and the pooled figures are worked from those. You can see that the first buy's 5,000.00 is still 5,000.00 after the split — it is now spread over 200.0000 shares instead of 100.0000, at 25.0000 each instead of 50.0000. Nothing was gained and nothing was lost; the same money is standing behind a different number of shares.
What is counted, and what is not
This page uses only the share counts, the prices and the ratio you type in. Nothing else goes into the arithmetic.
- The ratio is yours, not looked up. This page has no feed of corporate actions and does not know whether, when or at what ratio any company split. Type New and Old as the company states it. If you are not sure of the ratio, this page cannot tell you — go and read the announcement or your broker's note.
- Taxes are not counted. No capital gains tax, no withholding, no tax of any kind. A split on its own is not usually a taxable event, but what it does to your cost basis when you eventually sell is a tax question, and there is no field for one here. Every figure on this page is a before-tax figure.
- No live prices. This page never fetches a quote and has no connection to a market data source, so it can never show you a price that is not real. The price after the split is yours to type, and if you leave it out, the page simply stops at the share count and the costs.
- One split per run. This page applies one ratio once. If your shares went through two splits, run the first one, then type the result in as a fresh set of rows and run the second — every run is plain arithmetic and no state is carried between them.
- Fractional shares: one assumption, and a way around it. The page treats the position as one holding, so the fraction is worked on the total share count: if your broker only holds whole shares, the part after the decimal point is paid out in cash at the price after the split. If your broker rounds each lot separately instead, give each lot its own run — put that one buy in on its own and the fraction comes out for that lot alone.
- Not counted: fees and commissions on the buys, dividends, currency conversion, spin-offs, rights issues, and any other corporate action. There is no field for any of them. If you want a commission folded into a buy's cost, add it into that buy's price before typing it in.
- Not built: several tickers at once, importing a statement, saving your history, or signing in. There is no account here and nothing is stored.
The result describes the split you entered — these buys, this ratio, this price. It is not a view on what the split means for the company or for your holding, and this page takes no position on it.
Frequently asked questions
What does a stock split calculator work out?
From the figures you type: your share count before and after the split, the money you paid in, your average cost per share before and after, and your cost basis per share after. It also shows what each individual buy becomes. Add the price after the split and it adds the market value, the profit or loss, and the cash paid for a fractional share.
Is a share split calculator the same thing as a stock split calculator?
Yes — in everyday use both names mean the same tool, and this page answers to both. The arithmetic is identical whether you say "share split" or "stock split": the ratio is applied to the share count and its inverse to every per-share figure.
How do I enter a reverse split calculator's ratio — do I have to type it backwards?
No. Type it the way the company announced it. The two boxes are New and Old, in that order: a 1-for-10 reverse split is New 1, Old 10, and a 2-for-1 forward split is New 2, Old 1. The page works out the direction itself and tells you which one it read — "every 1 share becomes 2" or "every 10 shares become 1" — so you can see it read the ratio the way you meant it. This is also a reverse stock split calculator: both directions use the same pair of boxes.
What is a forward split, and what changes when it happens?
A forward split is a ratio greater than one — 2-for-1, 3-for-1, 10-for-1. You end up with more shares and each one is worth less. Your share count goes up, your average cost per share and your cost basis per share go down by the same factor, and the money you paid in stays exactly where it was. A reverse split is the same arithmetic with a ratio below one: fewer shares, each worth more.
Does a split change how much money I have in the position?
No, and that is the one thing worth holding on to. A split re-cuts the same position into a different number of pieces; it does not put money in or take it out. This page prints the money paid in twice — once as the figure before the split and once in the cost-basis line — and both read the same number. What moves is the share count and every per-share figure.
Why is the cost basis per share shown separately from the average cost after the split?
Because they are the same figure reached two different ways, and seeing both agree is how you check the arithmetic. The average cost after is the money paid in divided by the new share count. The cost basis per share is that same money divided by the old share count and by the ratio. Both are printed with their own line of working underneath, and both are rounded down, so the two should read the same number — a split divides your cost per share by exactly the factor it multiplies your share count by.
What happens to my fractional share?
If the split leaves you with a part of a share — most often after a reverse split — and your broker only holds whole shares, that part is usually paid out in cash at the price after the split. Type the price and the page works it out: the whole shares you keep, the fraction, and the cash it comes to, with the multiplication printed out. The page treats your holding as one position; if your broker settles each lot on its own, run each lot separately.
Can it tell me when a company splits, or what the ratio was?
No. This page has no corporate-actions feed and no market data of any kind, by design — a fetched ratio can be wrong, stale, or for the wrong company, and this page would rather show nothing than show a number it did not get from you. Find the ratio in the announcement or on your broker's note and type it in.
What if my shares went through more than one split?
Run them one at a time. Apply the first ratio, read off the new share count and the new cost per share, type those in as a fresh set of buy rows, then apply the second ratio. Each run is plain arithmetic and nothing is carried over between runs, so you can stop and check the figures at any point.
How many buys can I enter?
As many as you need. The page starts with two buys — one buy on its own just returns the price you typed — then use + Add buy for each extra one and the × on a row to remove it. There is no cap.
How is this different from the other calculators on this site?
They build the cost; this page carries it through a corporate action. The stock average calculator pools buys into an average cost, the average down calculator shows what one more purchase does to it, the DCA calculator takes the money you invest each period instead of the share counts, the stock profit calculator adds the fees on both sides and the sale, the dividend calculator works out what your shares pay you now, and the dividend reinvestment calculator handles dividends put back into shares. This is the one that takes an existing average cost through a split and back out the other side.
Does this page tell me what a split means for whether I should hold?
No, and nothing here should be read that way. A split is a re-cutting of the same position, and this page does the arithmetic on it without ranking it, comparing it to holding something else, or telling you what to do with your money. It answers one question only: given these buys and this ratio, what do my share count, my average cost and my cost basis become?
Does it work on my phone, and do I need an account?
Yes to the first, and no to the second. The fields stack to a single column on a narrow screen and the results stay inside the width of the page. There is no sign-up, no pop-up and nothing to install: the whole calculation runs in your browser, and your numbers are not sent anywhere.