In terms of calculating your returns, you can use this formula:
This formula applies for when you're going Long, hoping that the price of the market increases, however it's different if you're going Short, betting that the price decreases (in which case you can use the same formula, but multiply the Return in the end by negative one (-1).
Let's do an example:
AAPL is trading at $300, and I am using a leverage of 5. I make the trade, going Long Apple at $300 a share.
In a couple days I see the price has moved to $310. What's my potential profit?
( ( ($310 - $300) x 5 ) / $300 ) x 100 = 16.67%
If I invested 1000 MPH, I now have earned 166.7 MPH of profit.