I want to calculate by-myself 5 year return & STD for SPY ETF.
What I did:
- Downloaded to Excel from yahoo finance historical data for the ETF (daily Adj. Close) from
1/1/start_year to 1/1/start_year+5.
- (A) Calculated for each year in Excel
STDEV.Pbased on daily closed prices. (B) Calculated for each year return by
- (A) Simple Arithmetic
Averagefor the STD based on yearly STD's I have from above. (B)
Geomeanfor the return based on yearly returns I have from above (compound average).
Problem: The numbers far away from the figures we can find in Morningstar, yahoo finance etc. (Assume I work correct from the perspective of using numbers, percentages, +/-1, *100 etc...)
Question: This is a Math exercise not a real world finance one. Does from pure mathematical point of view I have mistakes? Which means that the deviations from the figures published in yahoo finance can be explained with taxes, dividends etc. real economic world. OR: I have mathematical mistakes and this is not the way how to compute this figures (in such case - I would like to know how what are the mistakes).