Two questions, one weighted average
Enter an additional quantity to see the average after that purchase. Enter a target average to see how many shares would be required at the stated purchase price. Both answers use the same weighted-average arithmetic.
A target must sit between the current average and the next purchase price. If it is equal to or below the purchase price, no finite quantity can reach it.
What a lower average does not do
A lower average does not reduce the total unrealised gain or loss at the moment of purchase. The larger position has a lower average, but it is exposed to more future price movement.
This calculator does not decide whether the additional exposure is appropriate. It shows the quantity and resulting average for the numbers entered.