How to Calculate VAT on an Invoice, Line by Line

To calculate VAT on an invoice, work out the VAT on each line (or on the subtotal after discounts), round consistently, add delivery and other charges before tax, and show the net, VAT and total separately. That is how to calculate VAT on an invoice so the client's accounts team can check every figure. The formula itself is simple; the mistakes happen with discounts, delivery, rounding and items at different rates.

The formula, applied to an invoice

For each line: quantity multiplied by the unit price gives the net line total. The net line total multiplied by the VAT rate as a decimal gives the VAT for that line. At 15%, a net line of 250.00 carries VAT of 250.00 x 0.15 = 37.50. Add up the net lines for the subtotal, add up the VAT, and the two together are the invoice total.

If you only need to check a single amount, our VAT calculator adds or removes VAT from one figure. An invoice needs a bit more, because it has several lines and usually some adjustments.

A worked multi-line invoice

An office supplies order at 15% VAT, with delivery charged on top:

The invoice then shows: net 2,218.70, VAT at 15% 332.81, total due 2,551.51. The toner line is the only one that needs rounding: 569.70 x 0.15 = 85.455, which rounds to 85.46.

Discounts and delivery charges

Discounts come off before VAT. If you give 10% off a net amount of 1,000.00, VAT is charged on the 900.00 the client actually pays: 900.00 x 0.15 = 135.00, for a total of 1,035.00. Charging VAT on the full 1,000.00 and then taking the discount off the total overcharges VAT. Early-payment discounts that the client may or may not take are treated differently in different countries, so check the rule where you are registered before offering one.

Delivery goes on before VAT, too. When you charge for delivering the goods you sold, the delivery charge is normally part of the same sale and carries VAT at the same rate as the goods. Put it on its own line with its own VAT, as in the example above, rather than adding it to the total after tax.

Rounding: per line or on the total

You can round the VAT on each line and add up the rounded amounts, or add up the net lines and work out the VAT once on the total. Most tax authorities accept either, as long as you apply it the same way every time. The two can differ by a cent or so:

Items at different VAT rates

Some invoices mix a standard-rated item with a reduced-rate or zero-rated one. Don't apply one blended rate. Work out the VAT line by line at each item's own rate, then total the lines by rate, and show a small summary at the bottom: net and VAT at the standard rate, net and VAT at the reduced rate, net at zero rate, then the total. That breakdown is what the client needs to claim the right amount of VAT back.

State Which Price You Mean

Label every price as "excl. VAT" or "incl. VAT." The calculations above start from prices excluding VAT; if your prices already include it, take the VAT out of each price first rather than applying the rate to the VAT-inclusive figure. Leaving it ambiguous is one of the most common reasons clients query an invoice total that is otherwise correct.

Our tax invoice generator takes the discount off and adds delivery before tax, works out the VAT once on that total, and shows the net, VAT and total separately along with your VAT number. Once you have seen how to calculate VAT on an invoice by hand, it is also a quick way to check your own sums.