Meet Priya. She runs a small ceramics studio in Manchester and just landed her first wholesale order: 200 mugs. She wants £9.50 per mug to land in her account after costs, so she quotes the buyer £9.50 each and feels good about it. Two weeks later her accountant asks where the VAT is. The UK standard rate is 20%, and because she is VAT-registered she should have charged £11.40 per mug — £9.50 net plus £1.90 of VAT she now owes to HMRC. On 200 mugs that is £380 she has to find out of her own margin, because she never built it into the price.
This is the trap that catches small sellers across every VAT and GST country: confusing the price you want to keep with the price the customer pays. They are not the same number. VAT is a consumption tax — the buyer ultimately pays it, and you are simply the collector who passes it to the tax authority. If you forget to add it on top, you are paying it yourself.
Here is the math Priya should have run before quoting. To add VAT to a net price, multiply by the rate: £9.50 × 20% = £1.90 of VAT, for a gross price of £11.40. The shortcut is to multiply the net figure by 1.20. At a 19% German rate the multiplier is 1.19; at a 25% Scandinavian rate it is 1.25. The rate changes, the method does not.
The reverse problem is just as common. Say the buyer agreed on a shelf price of £11.40 including VAT, and Priya needs to know how much of that is hers to keep versus how much belongs to HMRC. You cannot simply take 20% of £11.40 — that is the single most frequent VAT mistake, and it gives the wrong answer of £2.28. The VAT is 20% of the net price, not the gross. To extract it correctly you divide the gross by 1.20 to recover the net of £9.50, then subtract: £11.40 − £9.50 = £1.90 of VAT. Get the direction wrong on a 200-mug order and you misstate the tax by hundreds of pounds.
Getting this right matters beyond a single order. Quote inclusive of VAT when your customers are consumers who care about the sticker price; quote exclusive of VAT when you sell to other registered businesses who reclaim it anyway. Either way, the number you report and remit has to be exact, because the tax authority reconciles what you collected against what you declared. Enter your net or gross figure above, set your country's rate, and the calculator shows the VAT and the total instantly — so the next quote you send already has the tax built in.