Find previous weights from current weights & percent change

Oct 2008
7
0
Hi

Say that I have a stock portfolio with stocks that at the end of the day have the following weights:

Stock A : 10%
Stock B : 15%
Stock C : 40%
Stock D : 35%

The change in stock price during the day was:

Stock A : +5%
Stock B : +20%
Stock C : -10%
Stock D : +50%

From this information, can I find what weights the stocks had in the portfolio at the beginning of the day? (by eg. using a spreadsheet)
 

CRGreathouse

Forum Staff
Nov 2006
16,046
936
UTC -5
Increase (or decrease) all stocks by the given percentages, then divide by the new total to get the new weights.
 
Oct 2008
7
0
But I want to go the other way - I know the new weights but want to find the old weights.
 
Oct 2008
7
0
Thanks, now I got it. The weights at the beginning of the day were:

Stock A : 0.106053911
Stock B : 0.139195758
Stock C : 0.49491825
Stock D : 0.259832081