VAT / Sales Tax Calculator

Two everyday tax questions, one tool. Add mode answers "the shelf price is 100 — what do I actually pay?" Remove mode answers the harder one: "the receipt says 123 including 23 percent — what was the net?" Presets cover the rates you meet most often (5, 7, 8, 10, 15, 17, 19, 20, 21, 23 and 25 percent), or type any rate you like.

Extracting tax is where the arithmetic goes wrong, because subtracting the rate is not the inverse of adding it. A gross of 123 at 23 percent is a net of 100, not 123 minus 23 percent, which is 94.71 — an error of 5.29 on a single line. The correct operation is division by 1 + rate, and the gap widens as the rate does: at 25 percent the tax inside a gross of 100 is 20, not 25, so the naive answer is a quarter too large. The tool always divides, and shows net, tax and gross together so the three numbers can be checked against each other.

The net-to-tax ratio in the output is there for bookkeeping. When you are entering an inclusive invoice into a ledger that wants the halves separately, it lets you verify that the split you typed reconstructs the total you were charged, which catches a transposed digit that any single figure would hide.

What the calculator cannot decide for you is which rate applies. Most VAT and GST systems run several: a standard rate, one or more reduced rates for food, books, transport or medicine, and a zero rate that is legally different from being exempt — zero-rated sales still let the seller reclaim input tax, exempt ones do not. Rates also change by ministerial decision and by destination, so an invoice crossing a border may carry the buyer's rate rather than the seller's. Sales tax in the United States is a different animal again: it is levied once at retail rather than at each stage, it is added at the till rather than shown in the shelf price, and the combined state, county and city rate can differ from one street to the next.