How can I calculate total return of stock with partial sale?

You have only sold 200 shares for $4.75 from those bought for $3.15. So your profit on those 200 shares is $1.60 per share or $320 or 51%.

From that you have 110 shares left that cost you $3.15 and 277 shares that cost you $3.54. So the total cost of your remaining shares is $1,327.08 (110 x $3.15 + 277 x $3.54). So your remaining shares have a average cost of $3.429 per share ($1,327.08/387).

We don't know what the current share price is as you haven't provided it, nor do we know what the company is, so lets say that the current price is $5 (or that you sell the remaining 387 shares for $5 per share). Then the profit on these 387 shares would be $1.571 per share or $607.92 or 46%.

Your total profit would then be $320 + $ 607.92 = $927.92 or 47% (note that this profit neglects any brokerage or other fees, as you have not provided any).

Edit due to new info. provided in question

With the current share price at $6.06 then the profit on these 387 shares would be $2.631 per share or $1018.20 or 77%.

Your total profit would then be $320 + $1018.20 = $1338.20 or 75% (note that this profit neglects any brokerage or other fees, as you have not provided any).

There are many ways to calculate the return, and every way will give you a different results in terms of a percentage-value.

One way to always get something meaningful - count the cash. You had 977 (+ 31) and in the end you have 1.370, which means you have earned 363 dollars.

But what is your return in terms of percentage?

One way to look at it, is by pretending that it is a fund in which you invest 1 dollar. What is the fund worth in the beginning and in the end? The tricky part in your example is, you injected new capital into the equation.

Initially you invested 977 dollars which later, in the second period became worth 1.473. You then sold off 200 shares for 950 dollars. Remember your portfolio is still worth 1.473, split between 950 in cash and 523 in Shares. So far so good - still easy to calculate return (1.473 / 977 -1 = 50.8% return).

Now you buy share for 981 dollars, but you only had 950 in cash? We now need to consider 2 scenarios. Either you (or someone else) injected 31 dollars into the fund - or you actually had the 31 dollars in the fund to begin with. If you already had the cash in the fund to begin with, your initial investment is 1.008 and not 977 (977 in shares and 31 in cash). In the end the value of the fund is 1.370, which means your return is 1.370 / 1.007 = 36%.

Consider if the 31 dollars was paid in to the fund by someone other than you. You will then need to recalculate how much you each own of the fund. Just before the injection, the fund was worth 950 in cash and 387 in stock (310 - 200 = 110 x 3.54) = 1.339 dollars - then 31 dollars are injected, bringing the value of the fund up to 1.370. The ownership of the fund is split with 1.339 / 1.370 = 97.8% of the value for the old capital and 2.2% for the new capital. If the value of the fund was to change from here, you could calculate the return for each investor individually by applying their share of the funds value respective to their investment.

Because the value of the fund has not changed since the last period (bullet 3), the return on the original investment is (977 / 1.339 - 1 = 37.2%) and the return on the new capital is (31 / 31 = 0%).

If you (and not someone else) injected the 31 dollar into the fund, you will need to calculate the weight of each share of capital in each period and get the average return for each period to get to a total return. In this specific case you will still get 37.2% return - but it gets even more comlex for each time you inject new capital.

Treat each position or partial position as a separate LOT. Each time you open a position, a new lot of shares is created. If you sell the whole position, then the lot is closed. Done. But if you sell a partial quantity, you need to create a new lot. Split the original lot into two. The quantities in each are the amount sold, and the amount remaining. If you were to then buy a few more shares, create a third lot. If you then sell the entire position, you'll be closing out all the remaining lots.

This allows you to track each buy/sell pairing. For each lot, simply calculate return based on cost and proceeds. You can't derive an annualized number for ALL the lots as a group, because there's no common timeframe that they share.

If you wish to calculate your return over time on the whole series of trades, consider using TWIRR. It treats these positions, plus the cash they represent, as a whole portfolio. See my post in this thread: How can I calculate a "running" return using XIRR in a spreadsheet?

It's very complex, remember the shares sold take their total returns with them, ie. you've already had their profit so don't need to keep accounting for it.

Those bought have none and need to be calculated from their purchase date.

All that matters is what number of shares you're left with after all the transactions and what that amount of shares, and only that amount, has each individually returned.

What you have to do is, as suggested already, treat whatever you're left holding after each new share purchase transaction as a new individual lot. Assign a number to the shares. That lot number then has a date and a cost associated with it.

Initial purchase (new shares) = lot #1 First additional purchase (added shares total) = lot #2 Second additional purchase (added shares total) = lot #3 etc.

Then for any sales use a first in first out basis. So number of shares first sold taken from lot #1 then any sales exceeding the number of shares in lot #1 have to be taken from lot #2, then from lot #3 etc.

Each lot has a relevant date and purchase price so once you've got that the income and capital return for each share lot (and so individual shares within) can easily be calculated and the results added.

That sum of income and capital gain is then divided by the cost of all the lots still held which gives a total return of all the shares still held.

I'm in a similar situation, hold a lot of lines and just can't face the slog of sorting it all out.

You could use the time-weighted return, assuming bid and ask values are the same for the price point at valuations.

Including brokerage fees for net time-weighted return. (Exclude fees for gross return.)

1. investment value is 310*3.15 = 976.50
2. price now 4.75
   investment is worth 310*4.75 - 19.95 = 1452.55
   return is 1452.55/976.5 - 1 = 0.487506
   200 sold, 110 still held
   value = 110*4.75 = 522.50
3. price now 3.54
   investment is worth 110*3.54 - 19.95 = 369.45
   return is 369.45/522.50 - 1 = -0.292919
   277 bought, total held = 387
   value = 387*3.54 = 1369.98
4. price now 6.06
   investment is worth 387*6.06 - 19.95 = 2325.27
   return is 2325.27/1369.98-1 = 0.697302

TWR = (1 + 0.487506)*(1 - 0.292919)*(1 + 0.697302) - 1 = 78.52 %

There is no clear answer as to the cost basis for the shares sold, when shares have been bought at more than one price.

I would suggest whatever you do is consistent from one holding to another. I think for performance measures, First in first out makes the most sense. It seems less likely to overstate or understate current performance.

https://www.investopedia.com/terms/a/averagecostbasismethod.asp