Calculating percentage change in percentage values
The difference between two percentages should never be described as the percentage increase or decrease.
Percentage increase or decrease is calculated by taking the difference between the two values and dividing by the original value at which you were looking:
So 500 sales becoming 750 sales represents a 50% increase, whilst a 1% conversion rate that becomes 3% is a 200% increase.
If you wanted to refer to the difference between these two percentages then you need to be very careful:
There is not a 2% increase, there is a difference or an increase of 2 percentage points.
Also note that percentage decreases do not need a minus sign if you are using the word “decrease” (it’s kind of implied!):