Profit, markup and margin — markup and margin are not the same number.
Both are percentages, but they are taken from different bases. Mark-up is measured against the cost price, margin against the selling price. An item bought for 10 and sold for 15 euro carries a 50% mark-up but a 33.3% margin. Confusing the two is among the most common pricing errors.
Divide the cost by one minus the margin expressed as a fraction. To make a 40% margin on an item costing 10 euro, the price is 10 / (1 − 0.4) = 16.67 euro. Multiplying by 1.4 would give 14 euro, which is a 40% mark-up and a margin of only 28.6%.
It depends entirely on the sector and there is no single figure. Grocery retail often runs on a few percent; services and software run far higher. This calculator computes the ratio rather than judging it, and comparison only makes sense within your own sector.
No. What is calculated here is the gross margin, covering only the gap between cost and selling price. Rent, wages, transport, tax and everything else still have to come out of it. A business with a healthy gross margin can still run at a loss if the remaining costs consume it.