Trying to work out a formula for calculating my required sale price to ensure a fixed profit margin, when taking merchant costs and GST into account. For example, I resell a product that costs me $20 (inc GST) to purchase. I want to sell the product with a $15 profit margin after all my purchase costs are taken into account, including GST that I will owe the govt from the sale. It costs me 3% (inc GST) merchant fee to process transactions - which is calculated on the final sale price inclusive of GST. There are lots of products with different cost prices, but I want to make a flat $15 (or whatever) profit on all of them, regardless of cost price (as opposed to a % of cost). I'm not getting figures in my spreadsheet that seem correct when I do the calculations backwards - so I'm obviously adding the profit to the wrong figures. Any suggestions on how you would come up with a spreadsheet formula to calculate the requires sales price? Should I just be working on exGST figures and let GST take care of itself? I think that's where I'm over-complicating things ... trying to take my GST cost into account in the calculations.