How to calculate 5 years return & STD for ETF?

I want to calculate by-myself 5 year return & STD for SPY ETF.

What I did:

1. 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.
2. (A) Calculated for each year in Excel STDEV.P based on daily closed prices. (B) Calculated for each year return by end_year_price/start_year_price.
3. (A) Simple Arithmetic Average for the STD based on yearly STD's I have from above. (B) Geomean for 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).

Thanks,

• Returns are ( end_year_price -start_year_price)/start_year_price – sparkle Dec 5 '15 at 9:12
• @sparkle Thanks, I mentioned assume that from the perspective of working with percentages etc. I aligned the numbers. The bug is not here – michael Dec 5 '15 at 9:21