A price of 100 with 20% tax can produce a total of 120 or a total of 100, depending on a convention nobody stated. That ambiguity is the source of a surprising share of invoice disputes, and of a specific and expensive arithmetic error that quietly eats margin.
Tax-exclusive pricing quotes the amount before tax and adds it. Tax-inclusive pricing quotes the amount the customer actually pays, with tax already inside it. Which you use is partly a business decision, partly a consumer-protection requirement, and entirely something your invoice should make unambiguous.
The two conventions
Tax-exclusive pricing states the net amount. "£100 plus VAT" means the customer pays £120 at a 20% rate. This is the norm in business-to-business trade, because a VAT-registered buyer reclaims the tax and therefore thinks in net terms — the £20 is a pass-through that never affects their cost.
Tax-inclusive pricing states the gross amount. "£120 including VAT" is the same transaction described from the customer’s side. This is the norm in consumer-facing sales, where the buyer cannot reclaim anything and the only number that means anything to them is what leaves their account.
Neither is more correct. They describe the same money. What causes trouble is leaving it unstated, or switching between them without saying so.
| Tax-exclusive | Tax-inclusive | |
|---|---|---|
| Stated price | £100 | £120 |
| Net amount | £100 | £100 |
| Tax | £20 | £20 |
| Customer pays | £120 | £120 |
| Usual context | B2B | B2C / retail |
| What the buyer cares about | The net figure | The gross figure |
The arithmetic that costs people money
Extracting tax from a tax-inclusive price is where the classic error happens. If a price of £120 includes 20% VAT, the VAT is not £24. Taking 20% of the gross figure is wrong, because the 20% was applied to the net amount, not to the total.
The correct extraction divides rather than multiplies. Net = gross ÷ 1.20, so £120 ÷ 1.20 = £100, and the VAT is the £20 difference. For any rate r expressed as a decimal: net = gross ÷ (1 + r), and tax = gross − net.
The error is small per transaction and systematic across all of them, which is what makes it dangerous. Treating £24 as the tax on a £120 inclusive price overstates the tax by £4 and understates your revenue by the same amount on every single sale. Over a year of consumer transactions that is a material misstatement in both your VAT return and your accounts.
- From net to gross: gross = net × (1 + rate)
- From gross to net: net = gross ÷ (1 + rate)
- Tax from a gross figure: tax = gross − (gross ÷ (1 + rate))
- At 20%: £120 gross → £100 net, £20 tax. Not £24.
Which to use
For business customers, quote and invoice tax-exclusive. It matches how they evaluate the cost, makes comparisons with competitors meaningful, and reflects the reality that the tax is not part of their expense.
For consumers, show tax-inclusive prices. In many jurisdictions this is not merely convention but a consumer-protection requirement: advertised prices to consumers must show the total payable, and presenting a net price that becomes larger at checkout can breach price-display rules.
Where you sell to both, the cleanest approach is to display prices appropriately for each audience while keeping your internal records in net terms. Books, margins and reporting should all run on net figures regardless of how the price was presented, because net is the amount that is actually yours.
Making the invoice unambiguous
Whichever convention you use, the invoice should show the breakdown rather than a single number. State the net subtotal, the tax with its rate, and the gross total. A reader should be able to see all three without doing any arithmetic, and a customer’s accounting system needs the net and tax separately to book the transaction.
Label the prices explicitly. "Prices exclude VAT" or "All prices include VAT at 20%" on the invoice removes the ambiguity that causes disputes. Where different lines carry different rates — a mixed invoice with standard-rated and zero-rated items — group them or show tax per line, so the total is reconstructable.
The other habit worth keeping is consistency between the quote and the invoice. A quote presented tax-exclusive followed by an invoice presented tax-inclusive is the same money and looks like a price increase. More than one uncomfortable client conversation has come from nothing but a change of convention.
Common Mistakes
Taking a percentage of the gross to find the tax
20% of a £120 tax-inclusive price is £24, but the actual VAT is £20. Divide by 1 + rate to get the net figure, then subtract. The wrong method overstates tax on every transaction.
Quoting exclusive to consumers
Consumers evaluate the total they will pay, and many jurisdictions require prices displayed to consumers to be tax-inclusive. A net price that grows at checkout is both a bad experience and a possible compliance problem.
Switching convention between quote and invoice
The amounts may be identical while the headline number changes. To the client it reads as a price rise, and the conversation costs more than the consistency would have.
Reporting revenue gross
Tax you collect is not income; it is money you hold for the tax authority. Booking gross figures as revenue inflates your reported performance and produces a nasty correction when the return is filed.
Frequently Asked Questions
How do I calculate VAT from a tax-inclusive price?
Divide the gross by 1 plus the rate to get the net, then subtract. At 20%: £120 ÷ 1.20 = £100 net, so £20 VAT. At 5%: £105 ÷ 1.05 = £100 net, so £5 VAT.
Do I have to show prices including tax?
For consumer sales, many jurisdictions require it, so advertised prices must be the total payable. For business-to-business sales, tax-exclusive presentation is generally accepted and usually preferred. The invoice itself should show net, tax and gross regardless.
Which figure counts as my revenue?
The net amount. Tax collected is a liability owed to the tax authority, not income — which is why running your reporting on net figures matters even when you quote and sell tax-inclusive.
What if some items on the invoice are taxed differently?
Group items by rate or show tax per line, then subtotal each rate before the total. A single blended tax line on a mixed-rate invoice is difficult for a customer to verify and can fail invoice content requirements in VAT jurisdictions.
Sources & Further Reading
- VAT rates and how VAT is charged — GOV.UK
- VAT Directive 2006/112/EC — taxable amount and rates — EUR-Lex, European Union
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