Enter your price and your costs to see exactly what you make on every sale, your profit, your net margin and your markup. Most owners can name their revenue but not this. Now you can.
Say an item costs you £10 and you sell it for £20. Your profit is £10. As a margin (profit ÷ price) that's 50%. As a markup (profit ÷ cost) it's 100%. Same £10 profit, two very different percentages. If someone tells you to "add 50%" and you apply it as margin when they meant markup, you leave money on the table on every single sale.
The number most sellers should watch is net margin, because it's after the fees, postage and packaging that quietly eat the profit. Know it for your typical sale and you'll price with confidence.