This is probably more of a finance question and i just want to make sure im doing it right.
the question follows as.... calculate the % performance year over year for the past 1 year, past 2 years and past 3 years.
lets say the stock is AMAZON
yr 0 800
yr 1 850
yr 2 900
yr 3 950
yr 4 1000

to calculate the year over year as a % performance it would be... ((Old - new)/new)*100
or in this case...

over the past 1 years ((yr 0 - yr 1)/yr 1)*100
over the past 2 years ((yr 0 - yr 2)/yr 2)*100
over the past 3 years ((yr 0 - yr 3)/yr 3)*100

Year over year performance percentage would be new year divided by last year. 850/800=1.0625. This indicates 6.25% increase over the previous year. To validate your data simply multiply last year by this 1.0625 (or 106.25%) and you will have 800*1.0625=850.

Year 0 -- 800
Year 1 -- 850 (1.0625 or 6.25%)
Year 2 -- 900 (1.0588 or 5.88%)
Year 3 -- 950 (1.0555 or 5.55%)
Year 4 -- 1000 (1.0526 or 5.26%)

I cant find the edit button.... what i meant to say was

over the past 1 years (y1 - y0) / y0
over the past 2 years (y2 - y0) / y0
over the past 3 years (y3 - y0) / y0

Im comparing the change formula, and the yoy performance percentage and it gives me the same answer. there is no difference between the two equations is there? they both lead to the same outcome

the change formula would give me 6.25% and the YOY formula would give me 106.25% but i could just subtract 1 from the YOY formula to give me 6.25%

You are correct. Your way will give you only the percentage of improvement, or subtracting 1 (100%) from the 106.25% will have the same result.

much appreciated petro!