Investments can also give you a negative return.
For example you have 2,000 Telstra shares, valued at $8 each. You receive a dividend of $0.40 per share. The Telstra share price has decreased from $8 to $6.
So your total return can be calculated as follows:
Dividend received (2,000 x .40) $800
Less capital loss ((8-6) x 2,000) ($4,000)
Total return ($3,200)
Therefore you have made a total net loss on your Telstra shares over that particular time period of $3,200. This is a percentage loss of $3,200/$16,000, and it is a 20% loss on your original capital of $16,000.
It is impossible to predict what a return will be in the future, and unfortunately most data is historical. Hopefully this information is helpful in getting you thinking about a realistic expected return for an investment.