The Mark-up is the percentage of the cost to add to the cost of an item to derive the sale price. That means if the cost of an item is $100 and the mark-up percentage is 50% - the mark-up amount is $50 and the sale price is the cost ($100) plus the mark-up amount ($50) giving a total sale price of $150.
The main requirement is that you know the COST of an item to calculate the markup - but you can also imagine some people would want to enter a specific mark-up percentage and have the sheet calculate the Sales Price. So our example sheet lets you calculate the mark-up, or the sale price. Now, you can also calculate the cost - say if you were a buyer and knew the sale price and assumed some mark-up percentage - so we added that to the spreadsheet too.
