Andrew, rather than relying on such an outdated calculator, can you set up the appropriate equations in Excel? That way, you can customise it to your specific situation and even specific listings.

Use the information from https://www.ebay.com.au/help/selling/fees-credits-invoices/selling-fees-without-ebay-store?id=4822 to work out the fees; decide whether you’re going to use AP MyPost (and find out on what tier you’ll be, as that affects your discounts) or whether you’ll be using eBay labels (which I understand is not going to give you any postage discount) or Sendle (but read on these boards about what many eBayets think about that).

Work out what you’ll actually be charging for postage, and bear in mind you will be charged fees on the total transaction amount (including postage amount that the buyer pays you).