Normally I also use @promise444c5 way to calculate mine. But I think sir @Charles-Tim method also nice and fast too. Actually @promise444c5 way is the normal or should I say common way use in calculating profit or loss in business. Let me just emphasize on it Using the formulars:
Firstly SP = selling price, CP = cost price.
To calculate for profits,
Profit = SP - CP ( indicating that the selling price was higher or greater than the cost price ( your buying price))
While to calculate loss
Loss= CP - SP (While this formular shows that your cost price was higher or greater than your selling price) you made losses.
Formula for profit% and loss% profit percentage (profit%) = Profit/Cost price × 100
While loss percentage is .
Loss percentage (loss%) = Loss/Cost price × 100 , is just almos like profit% the only changes is that where you see profit just replace it with Loss (when solving for loss%)
Just decided to give some clarity concerning this topic posted. Hope this would be helpful to anyone it may concern please do so to correct me if there's any errors.