You Sold Your Winning Stock. Your Portfolio's Gain Percentage Just Fell, and You Didn't Lose a Rupiah
5 min read
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5 min read
You sell the one stock that made your year. A week later you check your portfolio's gain percentage, expecting it to look about the same. Instead it dropped, sometimes by a lot. Nothing else in the portfolio lost money. The remaining positions are worth exactly what they were worth before you sold.
This is not a bug and it is not bad luck. Your portfolio gain percentage is a blend of every position's own return, weighted by how much you paid for each one. Remove the position with the highest return, and the blend has to fall, because the number left over is a smaller, worse-performing group than the one you started with.
A portfolio's overall gain percentage is not one measurement. It is an average of every position's individual gain, weighted by its own cost basis.
Total gain ÷ Total invested capital
"Total invested capital" only counts what you currently have money in. The moment you sell a position completely, its cost basis leaves that denominator, and its gain leaves the numerator. What is left is the average of whatever you still hold, nothing more.
If the position you sold happened to be your best performer, the average left behind is necessarily lower than the average you had a moment ago. That is arithmetic, not a signal that your remaining holdings did anything wrong.
Say your portfolio holds two positions, in round numbers to keep the arithmetic visible.
| Position | Invested | Current value | Gain | Gain % |
|---|---|---|---|---|
| Stock A | Rp 10,000,000 | Rp 20,000,000 | Rp 10,000,000 | 100% |
| Stock B | Rp 10,000,000 | Rp 11,000,000 | Rp 1,000,000 | 10% |
| Portfolio total | Rp 20,000,000 | Rp 31,000,000 | Rp 11,000,000 | 55% |
That 55% is not an arbitrary average of 100% and 10%. It is weighted by how much money sits in each position, and here the two are equal in size, so it lands roughly in the middle.
Now sell Stock A entirely, at its full 100% gain, and hold the cash or move it elsewhere outside the portfolio.
| Position | Invested | Current value | Gain | Gain % |
|---|---|---|---|---|
| Stock B | Rp 10,000,000 | Rp 11,000,000 | Rp 1,000,000 | 10% |
| Portfolio total | Rp 10,000,000 | Rp 11,000,000 | Rp 1,000,000 | 10% |
The portfolio's headline gain percentage just went from 55% to 10%. Stock B did not change. You did not lose a rupiah, you locked in a real profit on Stock A. But the single number your app shows you dropped by 45 percentage points in an instant.
Most people read a portfolio's headline percentage as a running scoreboard: a single number that should only move because the market moved. It is not that. It is a live snapshot of a changing group of positions.
Two separate things are true after a sale like this. First, the trade itself: you converted a 100% unrealized gain into a real, banked one, which is unambiguously good. Second, the leftover average: your remaining book is now, on average, a worse performer than your closed-out book was, which is not a judgment on Stock B, just a fact about what is left in the sample.
Conflating the two produces a specific, avoidable panic: seeing a headline number fall and assuming a loss happened somewhere. The realized-versus-unrealized distinction is the other half of this same picture: the 45-point drop above coincided with a gain becoming real money, not with a loss.
The same composition effect runs in reverse. Sell your worst performer instead of your best, and the blended percentage on paper improves, again without anything about your remaining holdings changing. Neither move is inherently right or wrong. The point is that the headline percentage is not the right number to judge either decision by on its own.
Before reading a change in your overall gain percentage as news about performance, separate two questions:
NetWort's Gain Insights page breaks this down by position, not just the blended total, so a composition-driven move and a genuine price move do not get mistaken for each other. Checking a specific holding's own trend before deciding whether to trim it is worth doing on its Asset Detail page, which shows that position's return in isolation from the rest of the portfolio.