Net ↔ gross · any VAT rate

gross = net · (1 + VAT/100). Net is the price without tax, gross — with VAT added. The standard rate in Poland is 23%.
Converting a net price (without tax) to gross (with tax) and back:
Enter the amount, mark whether it is net or gross, and pick a VAT rate (in Poland the standard rate is 23%, with reduced rates of 8%, 5% and 0%). The calculator shows both prices and the VAT amount itself.
You divide the gross amount by (1 + VAT/100). For VAT 23%: net = gross / 1.23. You do not simply subtract 23% from the gross — that is a common mistake.
The standard 23%, reduced 8% (e.g. construction services) and 5% (e.g. food, books), and 0% for some goods. The calculator also handles custom rates.
Teaching? Embed this calculator on your site.
Free widget — paste it on your school site, blog or notes. It links to the full version.