MwSt.-Rechner

Divide the gross amount by 1 plus the rate — at 20% that is ÷ 1.20. So £120 gross is £100 net with £20 of VAT. Subtracting 20% from the gross is the classic mistake: it gives £96, which is wrong, because the 20% was charged on the net figure, not the gross one.

Standard 20% on most goods and services, reduced 5% (domestic fuel and power, children's car seats, some energy-saving materials) and zero 0% (most food, books and newspapers, children's clothing). Zero-rated is not the same as exempt — zero-rated sales still count toward your taxable turnover.

In the UK, once your VAT-taxable turnover passes the registration threshold in any rolling 12-month period, or if you expect to pass it within the next 30 days. The threshold is revised from time to time, so check the current figure with HMRC rather than relying on a number you have seen quoted.

Yes. Choose "Custom rate…" and enter any percentage — Ireland's 23%, Germany's 19%, the Netherlands' 21%, or any other VAT or GST rate. The maths is identical wherever the tax is charged as a percentage of the net price.

No — it is arithmetic. Which rate applies to a particular sale, and whether something is zero-rated or exempt, is a question for HMRC or your accountant.