StockAvg

Stock Split Calculator

Type every buy you made, then the split ratio — how many new shares for how many old ones. The page pools your buys into one average cost and applies the ratio to all of it: after the split, how many shares do I hold and what is my average cost per share? The money you paid in does not move by a penny — what changes is the share count and every per-share figure. The arithmetic is printed underneath, using your own numbers.

Each buy

Shares bought Price per share After the split

The split

Split ratio — new for old
-for-
Write it the way the company writes it. A 2-for-1 split is New 2, Old 1. A 1-for-10 reverse split is New 1, Old 10 — you never have to type a ratio backwards. This page does not know or guess when a company splits: the ratio is yours to type.
Price per share after the split — optional Leave it empty and the page stops at the share count, the average cost and the cost basis per share. Type it and the page adds the market value, the profit or loss, and the cash a broker pays you for a fractional share. No live price feed here: the price is yours to type.
Shares after the split —
Average cost after the split —
Shares before —
Money paid in — unchanged —
Average cost before —
Cost basis per share after — money in ÷ shares before ÷ ratio —

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.

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.

The same money either side of a split A two for one split: before it, 150.0000 shares at an average cost of 53.3333 stand behind 8,000.00 paid in; after it, 300.0000 shares at an average cost of 26.6666 stand behind the same 8,000.00. A one for ten reverse split runs the same arithmetic the other way: 15.0000 shares at 100.0000 each, 1,500.00 paid in, become 1.5000 shares at 1,000.0000 each, still 1,500.00 paid in. A 2-for-1 split: the money does not move, the two figures above it do Before 150.0000 shares avg cost 53.3333 8,000.00 paid in After 300.0000 shares avg cost 26.6666 8,000.00 paid in The bar is twice as long and the figure on it is half as big. That is the whole of what a forward split does. A 1-for-10 reverse split runs the same arithmetic the other way 15.0000 shares x 100.0000 = 1,500.00 paid in becomes 1.5000 shares x 1,000.0000 = 1,500.00

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.

The cash paid for a fractional share is not all profit

When a split leaves you holding part of a share and your broker settles that part in cash, the money arrives looking like a small windfall. Most of it is your own capital coming back. The fraction carries a cost basis of exactly the same kind as the whole shares do: the fraction multiplied by your cost per share after the split.

Take a position built in two buys: 45 shares at 100.00 and 30 shares at 120.00, run through a 3-for-2 split. Money paid in is 4,500.00 + 3,600.00 = 8,100.00 for 75.0000 shares, an average cost of 108.0000 before the split. The ratio is 3 ÷ 2 = 1.5, so the position becomes 112.5000 shares at a cost per share of 72.0000. Half a share is left over, and at a price of 80.00 after the split the broker pays 0.5000 × 80.00 = 40.00 for it.

Of that 40.00, the part that was already yours is 0.5000 × 72.0000 = 36.00, and 40.00 − 36.00 = 4.00 is everything else. Split the rest of the position the same way and the two add back to the profit the page already prints: 112 whole shares worth 8,960.00 against a basis of 112 × 72.0000 = 8,064.00 is 896.00, and 896.00 + 4.00 = 900.00, which is the profit line above. The split did not create the 4.00. It is the gain the half share already had, settled in cash instead of in stock.

How much of that payment is your own money is not fixed by the split at all. It is your cost per share divided by the price. Same position, same ratio, same half share, only the price after the split moves:

Price after the splitCash for the fractionYour basis in itThe rest is gainBasis as a share of the cash
72.0036.0036.000.00100.00%
80.0040.0036.004.0090.00%
100.0050.0036.0014.0072.00%
144.0072.0036.0036.0050.00%

Basis as a share of the cash = cost per share after the split ÷ price after the split

Check it against the last column: 72.0000 ÷ 72.00 = 100.00%, 72.0000 ÷ 80.00 = 90.00%, 72.0000 ÷ 100.00 = 72.00%, 72.0000 ÷ 144.00 = 50.00%. The blue block in every row of the diagram below is the same 36.00, because nothing about the price changes what the half share cost you.

The first row is the one worth sitting with. At 72.00 the price after the split equals your cost per share, so the whole payment is your own money and the gain on it is 0.00. That is not a special property of splits, it is what break-even means on half a share. The ratio decided how much of your position was settled in cash; how much of that cash is profit was decided by the price, and the ratio had nothing to do with it.

The same reading runs on a reverse split, where there is usually more cash at stake. 15 shares at 100.00 is 1,500.00 paid in. A 1-for-10 reverse split turns that into 1.5000 shares at a cost per share of 1,000.0000. At 1,100.00 after the split the broker pays 0.5000 × 1,100.00 = 550.00 for the half share, and 0.5000 × 1,000.0000 = 500.00 of it is your own basis. A payment of 550.00 carries 50.00 of gain, which is 9.09% of what was handed over.

What this page settles is the split side of that: how much of the payment is basis and how much is left over. Whether the leftover is taxed, at what rate and in which year depends on your own tax position, and there is no field for any of it here. Every figure on this page is a before-tax figure.

The same half share at four prices: how much of the cash was already yours Four horizontal bars, one for each price after the split. Each bar is the cash paid for a half share, split into two parts: the blue part is the cost basis of the fraction, always 36.00, and the green part is the rest, which is the gain. At a price of 72.00 the cash is 36.00 and all of it is basis. At 80.00 the cash is 40.00 with 36.00 of basis. At 100.00 the cash is 50.00 with 36.00 of basis. At 144.00 the cash is 72.00 with 36.00 of basis. The same half share at four prices: how much of the cash was already yours 45 at 100.00 and 30 at 120.00, a 3-for-2 split: 112.5000 shares at 72.0000, half a share paid out in cash your own basis, 0.5000 x 72.0000 = 36.00 the rest is gain price 72.00 36.00 cash, 100.00% basis price 80.00 40.00 cash, 90.00% basis price 100.00 50.00 cash, 72.00% basis price 144.00 72.00 cash, 50.00% basis The blue block never moves: 36.00 is what the half share cost you whatever the price does. At 72.00 the price equals the cost per share, so the whole payment is basis and the gain on it is 0.00. Every figure rounded down.

A cash-in-lieu payment is two things at once: the basis of the fraction coming back to you, and the gain on it. The split decides how big the payment is; the price decides what share of it was yours already.

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 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.

What does a 1.5 stock split mean?

It is a split ratio written as a number instead of as a pair: every share you hold becomes one and a half. Companies announce the same thing as 3-for-2, and this page wants it typed that way round, New 3 and Old 2, which the page then reads as a ratio of 1.5. On 100 shares at 60.00 the split gives 150.0000 shares at a cost per share of 40.0000, and the 6,000.00 you paid in does not move.

The part worth watching is the halves. A ratio with a half in it leaves half a share behind whenever your share count is odd: 75 shares become 112.5000, and that 0.5000 is the piece a broker settles in cash. Even counts come out whole, so 40 shares become 60.0000 and nothing is paid out. If you want to know what that cash is made of, the section above splits it into the basis coming back to you and the gain on top of it.

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.

This page is a calculator, not investment advice. A split is arithmetic, not a reason to buy and not a reason to sell. Contact: contact@stockavg.com