What is the difference between return and interest?

Return: The percentage of loss & gain generated by an investment in return. A return is an internal measure to the investor. 

Formula: Ending value of investment - Beginning value of investment / Beginning Value of investment x 100

Interest: The cost of borrowing or lending money is interest. Interest is an external measure that relates to the cost of getting money from a lender. 

Simple interest formula is given:    

         SI = (P × R ×T) / 100

where 
SI = simple interest
P = principal
R = interest rate (in percentage)
T = time duration (in years)

The compound interest formula is given as:  

       A = P(1+R/n)^nt

Where,
A = amount
P = principal
R = rate of interest
n = number of times interest is compounded per year
t = time (years)