Tax, Salary & Business

Work Out VAT: Add Tax or Remove It from a Total

Calculate VAT from net and gross prices, reverse an inclusive total correctly, and separate arithmetic from tax-rate and invoice requirements.

By Uddhav Gopani, FounderPublished 25 September 2026Reviewed 29 September 2026

Work Out VAT: Add Tax or Remove It from a Total

Separate the net price, tax and gross total

For a price excluding VAT, the net amount is the starting value. VAT is added to produce the gross amount paid. If the applicable percentage rate is r, write its decimal form as r/100. VAT equals net×r/100, and gross equals net×(1+r/100). These equations describe the arithmetic once the correct rate and treatment are known. The rate itself depends on jurisdiction, supply and circumstances. An example using 20% illustrates the calculation and does not mean every transaction is taxable at that rate.

Add VAT to an exclusive price

Suppose the net price is 250 and the applicable illustrative rate is 20%. The tax is 250×0.20=50, so the gross total is 300. Keep the currency consistent across the calculation. If an invoice contains five identical items at 50 net each, the combined net amount is also 250 before any discounts or extra charges. Establish whether displayed prices are exclusive or inclusive before entering them. Adding VAT again to a price that already includes it overstates the amount payable.

Remove VAT from an inclusive total

To recover the net amount from a gross price, divide by 1+r/100. For a gross total of 300 at 20%, net is 300/1.20=250 and tax is 300-250=50. Subtracting 20% of 300 gives 240, which is incorrect because the percentage was defined relative to the net price. The tax share of a gross price at 20% is 20/120, or one sixth, rather than one fifth. This difference is the main source of errors when working backward from a till receipt.

Use the direct gross-tax formula

The VAT portion of an inclusive total is gross×r/(100+r). For a gross amount of 115 at an illustrative 15% rate, tax is 115×15/115=15 and net is 100. At a zero rate, the equations give zero tax and identical net and gross amounts. That arithmetic does not mean zero-rated and exempt supplies have identical legal treatment. Do not infer reporting or recovery rights from the fact that both display no added tax in a simple price calculation. Those classifications require the applicable tax rules.

Apply discounts and mixed rates deliberately

If a 10% discount reduces a net price of 200 to 180 before tax, a 20% tax calculation produces 36 tax and a gross total of 216. A mixed-rate invoice requires separate net subtotals for each rate. For example, 100 at 20% and 100 at 5% produce 20+5=25 tax on 200 net, for 225 gross. Applying one rate to the full invoice would misstate the tax unless the classification actually permits it. Fees and delivery charges also need their correct treatment before summing the invoice.

State a rounding convention

Currency amounts often need rounding to the smallest currency unit. Rounding each line's tax can differ from computing tax on a combined subtotal and rounding once. Three lines at 0.03 net with 20% tax each produce 0.006 tax per line; rounding individually to 0.01 totals 0.03, whereas the combined 0.09 net produces 0.018, which rounds to 0.02. Follow the applicable invoicing rules and system convention. Preserve unrounded intermediate values for comparison, and explain a small residual rather than silently altering a line to force a match.

Check the calculator against the invoice basis

Choose add VAT for an exclusive price or remove VAT for an inclusive price, enter the amount and the percentage rate, and confirm that net plus tax equals gross. Run 250 at 20% in add mode and 300 at 20% in remove mode as inverse checks. The linked tool performs the numerical conversion; it does not determine registration requirements, tax points, recoverability or the rate applicable to a particular supply. Use the current tax authority guidance and the actual invoice when those decisions matter. Keep the rate, amount basis and rounding method beside the result.

Use the VAT Calculator

Open VAT Calculator

Source and scope

GOV.UK charging and recording VAT