How VAT Is Calculated in the UK

When working with VAT, three terms come up constantly: net (the price before VAT), VAT (the tax itself), and gross (the total including VAT). Understanding these is essential before doing any VAT calculation.

Net + VAT = Gross. If you know any two of these, you can calculate the third.

To add VAT to a net amount, multiply by the VAT rate and add it to the original price. At the standard rate of 20%:

Net amount × 1.20 = Gross amount (including VAT)

Example: £500 × 1.20 = £600. The VAT is £100.

To remove VAT from a gross amount, divide by 1 plus the VAT rate. At 20%:

Gross amount ÷ 1.20 = Net amount (excluding VAT)

Example: £600 ÷ 1.20 = £500. The VAT is £100.

A common mistake is to simply subtract 20% of the gross amount — this gives the wrong answer. £600 × 20% = £120, which is incorrect. The right method is to divide by 1.20.

The same formula works for any VAT rate. For the reduced rate of 5%, multiply or divide by 1.05. For zero-rated items, no VAT is applied.

Example at 5%: £200 × 1.05 = £210 (VAT = £10). Removing: £210 ÷ 1.05 = £200.

When extracting VAT from a gross amount, you can use the VAT fraction. At 20%, the fraction is 1/6. So: £600 × (1/6) = £100 VAT.

At 5%, the fraction is 1/21. This shortcut is useful for mental arithmetic and quick checks.

Write the VAT rate as a decimal before calculating. At 20%, the decimal rate is 0.20; at 5%, it is 0.05. The same three formulas then work for any valid rate:

• VAT from net: net × rate = VAT.
• Gross from net: net × (1 + rate) = gross.
• Net from gross: gross ÷ (1 + rate) = net.

For £240 net at 20%, VAT is £240 × 0.20 = £48 and gross is £240 × 1.20 = £288. Starting with £288 gross, £288 ÷ 1.20 returns £240 net. The extracted VAT is the difference: £288 − £240 = £48.

Keep more precision during the calculation and round the displayed money at the end unless the invoice method requires line-level rounding. Repeatedly rounding intermediate percentages can create avoidable penny differences.

A 20% VAT charge is 20% of the net price, not 20% of the final gross price. If net is £100, VAT is £20 and gross is £120. The VAT therefore represents £20 ÷ £120 = one sixth, or about 16.67%, of the gross amount.

Subtracting 20% from £120 gives £96, which cannot be the original net because adding 20% to £96 produces only £115.20. Dividing £120 by 1.20 correctly returns £100. The same reasoning gives a gross-price VAT fraction of rate ÷ (100 + rate): 20 ÷ 120 = 1/6, and 5 ÷ 105 = 1/21.

This distinction is the main reason “add VAT” and “remove VAT” are not inverse percentage buttons. One starts from a net base; the other starts from a total that already contains the tax.

The UK standard rate is 20%, the reduced rate is 5%, and some supplies are zero-rated. The correct treatment depends on what is supplied, who receives it, where it is supplied and whether a specific condition is met. A calculator cannot determine that treatment from the price alone.

Zero-rated and exempt are not the same. A zero-rated supply is taxable at 0% and normally remains part of taxable turnover; an exempt supply is outside VAT charging and can affect whether related input VAT is recoverable. Check the official VAT-rates guidance before using 0%.

If a transaction includes items with different treatments, calculate each line or rate group separately. Applying one rate to the entire invoice can produce the wrong VAT even when the arithmetic itself is correct.

This calculator rounds displayed money values to the nearest penny. Real invoices may calculate VAT for each line and then total the rounded values, or calculate on a rate-level total. Small penny differences can therefore appear between two valid-looking methods.

Keep the original net amount, rate, VAT amount and gross amount together when checking a calculation. For a VAT invoice, also follow HMRC's invoice rules and retain the evidence needed for your records. Do not use an extracted VAT amount as proof that VAT is recoverable.

For a quick reasonableness check at 20%, VAT added should equal one fifth of the net price, while VAT inside a gross price should equal one sixth of that gross price. At 5%, the corresponding gross-price fraction is one twenty-first.

Suppose an invoice contains £300 net of standard-rated supplies and £200 net of reduced-rated supplies. Calculate each rate group separately:

• £300 × 20% = £60 VAT, giving £360 gross.
• £200 × 5% = £10 VAT, giving £210 gross.
• Total net is £500, total VAT is £70, and total gross is £570.

Applying 20% to the whole £500 would produce £100 VAT and overstate the tax by £30. Applying a blended rate without preserving the line classifications would make the invoice hard to verify. Group lines by treatment, calculate each group and retain the rate next to its taxable value.

If an invoice also contains zero-rated or exempt items, label them correctly rather than combining both as “0%”. Their arithmetic may look similar on the sale, but their VAT and input-tax consequences are different.

The VAT added to taxable sales is usually called output tax. VAT on eligible business purchases may be recoverable as input tax. A VAT return brings those figures together under the applicable rules; it is not simply 20% of turnover or the sum of every VAT amount found on receipts.

Input VAT recovery depends on valid evidence, business use and the nature of the supply. Exempt activities, private use, special schemes and restricted costs can change what is recoverable. The calculator does not decide recovery or produce VAT-return boxes.

Use the arithmetic tool when the rate and tax treatment are already known. Use bookkeeping records and HMRC guidance for return preparation, and get specialist help where partial exemption, imports, exports, reverse charge, margin schemes or cross-border place-of-supply rules apply.

VAT should follow the taxable amount for the transaction. If a discount changes the amount actually charged, calculate VAT on the price after the relevant discount rather than on a higher list price that the customer never pays. State whether a quoted discount is applied before or after VAT so the invoice can be checked.

When a completed sale is reduced or refunded, the business may need a credit note and corresponding record adjustment. Reversing the gross cash amount without preserving the original net, VAT and rate can leave sales records inconsistent with the VAT return.

Deposits, vouchers, bad-debt relief and changes in consideration can have timing or documentation rules beyond this arithmetic guide. The safe control is to retain the original invoice, the reason for the adjustment and the document that changes it. Use accounting software or professional advice for return treatment; use the calculator only to check a known net, rate and gross relationship.

The formulas above work well for standard-rated goods and services. However, VAT can be more complex when dealing with mixed supplies, partial exemptions, the Flat Rate Scheme, or cross-border transactions.

If your situation involves any of these, it's worth checking HMRC's detailed guidance or consulting a VAT-registered accountant. Our VAT calculator handles standard add/remove calculations at any UK rate.

Before relying on a number, write down the supply, customer, place of supply, price basis and rate source. If any of those facts are uncertain, the unresolved issue is tax treatment rather than multiplication. Resolve that question first, then use the calculator as an independent arithmetic check against the invoice or bookkeeping entry.