Guides
Short answers to the questions behind our tools – each with a worked example computed with the same formulas as the tool, and the sources we rely on.
Black Week
Planning a sale? Start with these before you set your discounts.
Profit, prices and discounts
- Gross or net? Calculating prices and margins with VATHow to convert gross and net prices, why your margin is always calculated on the net price, and what changes without VAT registration – with a country table.
- How to calculate your selling price from costs and target profitWork backwards from the profit you want to the price incl. VAT: fees, shipping, returns and ads included. Formula, worked example and a table by target margin.
- Contribution margin per order: how to calculate it in an online shopWhat one order leaves after all its variable costs, and how many orders cover your fixed costs. Formula, worked example and a table by order volume.
- Black Friday 2026: which discount can you afford?A table by margin: how many times more you must sell at 10–50 % off, the maximum discount for each margin and why sale-week ad costs change the answer.
- How to raise prices without losing customersBefore you raise a price, calculate how many sales you could lose and still earn the same. Then test it on a few products, step by step, with real numbers.
- How to find the products that lose money in your catalogueOne product is not your shop. How to check every product's profit with a CSV file, spot the loss makers and decide what to do with each – free for 10 products.
- Break-even price: the lowest price that still covers your costsThe lowest selling price at which an order covers all variable costs – with VAT, percentage fees and returns. Formula, example and a table by marketplace fee.
- Purchase price went up: how much do you need to raise your price?Purchase price up? The same percentage on the selling price is rarely right. Calculate the price that keeps your margin or your profit per order.
- How much more do you need to sell after a discount?Why 20 % off can need 2–3× the orders: the formula for the required sales increase, a table for 5–30 % discounts and a Black Friday checklist.
- How to calculate profit margin in e-commerceProfit margin step by step for online sellers: net price, every variable cost per order, contribution and margin – with formula and a worked example.
- Margin vs. markup: the difference and how to convertMarkup is profit relative to cost, margin is profit relative to price. Formulas to convert between them, a conversion table and a worked example.
Platform fees
- Etsy fees explained: listing, transaction, payment and Offsite AdsWhat Etsy takes per order: listing fee, transaction fee, payment processing and optional Offsite Ads, with the official rates, a worked example and a table.
- Payment fees per order: percentage or fixed fee – which is cheaper?How to compare payment providers for your shop: the cart value at which a lower percentage beats a lower fixed fee, with a worked example and a table.
- Platform and payment fees compared: what you can actually changeFees per order on Shopify, Etsy and Amazon for the same product – from the official price pages – and the fee settings you can really change yourself.
- Shopify fees explained: plans, card rates and transaction feesWhat Shopify really costs per order: plan price, Shopify Payments card rates, international cards and the extra fee for external providers – official rates.
- Amazon seller fees explained: referral fees, tiers and plansHow Amazon referral fees work: rates per category, tiers, minimum fee, the Prime rule for clothing and the selling plans – from Amazon's official pages.
Shipping
- EU parcel duties 2026 explained: €3 duty and €2 feeSince 2026 parcels from outside the EU cost €3 duty and €2 fee per item plus import VAT. What changed, who pays and what is still unconfirmed.
- Parcel prices 2027: how to recalculate your prices and free-shipping thresholdCarrier prices change on 1 January 2027. How to recalculate your shipping fee, product price and free-shipping threshold with your own new parcel price.
- Free shipping threshold: how to set one without losing moneyFree shipping from which order value? Calculate the threshold at which a free-shipping order earns as much as an order where the customer pays shipping.
Advertising
- How much ad cost per order can you afford?Your maximum ad cost per order is what an order leaves before advertising. How to calculate it, set a safe target and act when ads eat your profit.
- Break-even ROAS: which ROAS do your ads need?Break-even ROAS = revenue per order ÷ contribution before ads. Why 1 ÷ margin is too optimistic, with VAT, fees and returns, and a worked example.
Returns
Product feed (Google Shopping)
- Turn a Shopify or WooCommerce export into a valid Google Shopping feedWhich columns of a Shopify or WooCommerce export map to Google attributes, what is missing (link, availability, GTIN, currency) and how to check the file.
- Google Shopping product titles and descriptions: the rules that cause problemsTitle length, capital letters, promotional text and HTML in the description: what the Feed Validator flags in a Google Shopping feed, with a worked example.
- Google Shopping price format: how to write price and sale_priceWhy Merchant Center rejects prices like “19,99 €”: the required format 19.99 EUR, currency codes, VAT, sale_price rules and how to fix a whole feed at once.
- Missing attributes in Merchant Center: what Google requiresWhich product attributes Google requires for every product, which only for some (brand, GTIN, colour, size), allowed values and how to find gaps in a feed.
- Invalid GTIN in Google Merchant Center: causes and fixesWhy Google rejects a GTIN: wrong length, wrong check digit, restricted prefixes or the wrong product. How to check a GTIN and what to do if a product has none.