Reverse VAT Calculator
Type a UK gross (VAT-inclusive) amount and pick the rate. The calculator splits it into net and VAT and shows the VAT fraction used. Use this to reverse-engineer supplier receipts, simplified VAT invoices, or any total that includes VAT but does not break it out.
The math behind reverse VAT
Reverse VAT is the inverse of adding VAT. If gross = net × (1 + rate ÷ 100), then net = gross ÷ (1 + rate ÷ 100). The VAT amount is gross minus net.
The VAT fraction simplifies the calculation into a single multiplication. At 20% the fraction is 20/120, which reduces to 1/6. At 5% it is 5/105, which reduces to 1/21. The fraction is always the rate divided by (100 + rate), with the gross as the implicit denominator.
VAT fractions at common rates
| Rate | VAT fraction (full) | VAT fraction (simplified) | Use case |
|---|---|---|---|
| 0% | 0 / 100 | 0 | Zero-rated supplies — books, food, children's clothing |
| 5% | 5 / 105 | 1/21 | Reduced rate — domestic energy, mobility aids |
| 10% | 10 / 110 | 1/11 | Reduced rate in many overseas jurisdictions |
| 12.5% | 12.5 / 112.5 | 1/9 | UK hospitality temporary rate (2020–2022) |
| 15% | 15 / 115 | 3/23 | Reduced rate used internationally |
| 17.5% | 17.5 / 117.5 | 7/47 | UK historical standard rate (1991–2008, 2010) |
| 20% | 20 / 120 | 1/6 | UK standard rate since January 2011 |
| 23% | 23 / 123 | 23/123 | Standard rate in several EU member states |
| 25% | 25 / 125 | 1/5 | Standard rate in Scandinavia |
Worked examples
Example 1 — Extract VAT from £120 gross at 20%
VAT fraction: 20 / 120 = 1/6
VAT: £120 × 1/6 = £20.00
Net: £120 − £20 = £100.00
Cross-check: £100 × 1.20 = £120. Confirmed.
Example 2 — Reduced rate: £105 gross at 5%
VAT fraction: 5 / 105 = 1/21
VAT: £105 × 1/21 = £5.00
Net: £105 − £5 = £100.00
Use this for domestic energy bills, children's car seats, and mobility aids installed for over-60s. The 5% rate appears on the bill but the supplier may show only the gross total.
Example 3 — Awkward gross: £427.86 at 20%
VAT: £427.86 × 1/6 = £71.31 (rounded to nearest penny)
Net: £427.86 − £71.31 = £356.55
For non-round numbers, calculate the VAT to the nearest penny first, then derive the net by subtraction. Going the other way — net ÷ rate then summing — can produce a 1p discrepancy because of compound rounding.
Example 4 — Historical UK rate: £117.50 gross at 17.5%
VAT fraction: 17.5 / 117.5 = 7/47
VAT: £117.50 × 7/47 = £17.50
Net: £117.50 − £17.50 = £100.00
The 17.5% rate was the UK standard rate until January 2011 (with a temporary drop to 15% in 2008–2009). Useful when reconciling older invoices or working with archived contracts.
When to use reverse VAT
- Simplified VAT invoices. Retail receipts under £250 gross only need to show the total and the VAT rate. Reverse VAT extracts the input VAT for your records.
- Petty cash claims. Staff expense receipts usually arrive as a gross figure. Extract the VAT line by line for the Box 4 entry on the VAT return.
- Competitor pricing. A B2C competitor advertising gross prices includes VAT. Reverse VAT shows what they actually charge net — useful for like-for-like B2B comparisons.
- Quote reconciliation. An unclear quote labelled "all-in £600" may or may not include VAT. Reverse VAT against the standard rate gives the implied net so you can ask the supplier to confirm.
- Pricing on consumer products. Setting a £19.99 sticker price means net is £16.66 at 20% VAT. Reverse VAT works backwards from the desired shelf price to the wholesale price you need to negotiate.
Common reverse VAT mistakes
- Multiplying the gross by 20% instead of 1/6. 20% of £120 is £24, not £20. The fraction is rate ÷ (100 + rate), not rate as a decimal.
- Using the wrong rate. A 5% supply reverse-calculated at 20% over-states the VAT by a factor of four.
- Reversing a "+ VAT" quote. Quotes marked "+ VAT" or "ex VAT" are already net — running reverse VAT on them double-deducts the tax.
- Compounding rounding errors. Building gross from rounded net + rounded VAT is fine. Working the other direction — gross ÷ rate then summing — can produce 1p drift.
- Forgetting the receipt needs a VAT number. Reverse VAT only gives a reclaimable input VAT figure if the receipt or invoice carries the supplier's VAT registration number.
Frequently asked questions
How do I work out VAT from a gross figure?
Use the VAT fraction. At 20% multiply the gross by 1/6 to get the VAT directly. The net is gross minus VAT.
So £120 gross at 20% gives VAT of £20 and net of £100. For any rate, the formula is: VAT = gross × rate ÷ (100 + rate). At 5%, the fraction is 1/21. At 25%, it is 1/5. The shortcut is the same whether you are checking a till receipt or reconciling a supplier invoice.
What is the VAT fraction?
The proportion of a gross VAT-inclusive amount that represents the VAT itself. Formula: rate ÷ (100 + rate).
At the UK standard rate of 20%, the fraction is 20/120 = 1/6. At the reduced rate of 5%, it is 5/105 = 1/21. At a hypothetical 25%, it is 25/125 = 1/5. Multiply any gross figure by the fraction to extract the VAT in one step — useful when the invoice or receipt shows only a total.
Why is the VAT fraction at 20% equal to 1/6?
Because £120 (gross) = £100 (net) + £20 (VAT), so the VAT is 20/120 of the gross. That simplifies to 1/6.
Mathematically: rate ÷ (100 + rate) = 20 ÷ 120 = 1/6. The fraction always uses the gross as the denominator, not the net. People who instinctively use 20% (1/5) of the gross over-state the VAT by 20%. The fraction is the safe shortcut.
How do I extract VAT from a gross figure at 5%?
Multiply the gross by 1/21. So £105 gross at 5% gives £5 of VAT and £100 net.
For larger numbers, the same fraction applies: £2,100 gross = £100 VAT, £2,000 net. The 5% reduced rate applies to specific UK supplies including domestic energy, children's car seats, and mobility aids installed for over-60s. Confirm the rate is correct before using the calculator.
Can I reverse-calculate VAT at any rate?
Yes. The formula generalises: net = gross ÷ (1 + rate ÷ 100); VAT = gross − net.
So at 12.5%, a £900 gross gives net = 900 ÷ 1.125 = £800; VAT = £100. The VAT fraction at 12.5% is 12.5 ÷ 112.5 = 1/9. Useful when you encounter historical rates (UK was 17.5% before 2011) or non-UK rates on imported records. Always check the rate matches the document date.
What rate applies on UK VAT receipts that show only a total?
A simplified VAT receipt under £250 gross may show only the total plus the rate. Apply the standard 1/6 fraction to extract the VAT.
Receipts that mix rates — common at supermarkets where food is 0% and confectionery is 20% — itemise each rate separately. Petrol receipts at the pump usually show net, VAT, and gross in three lines. If a receipt shows no VAT number at all, you cannot reclaim the VAT regardless of the math.
How does reverse VAT differ from the reverse charge?
Reverse VAT is the arithmetic of splitting a gross into net + VAT. The reverse charge is a VAT accounting mechanism where the customer accounts for VAT instead of the supplier.
They sound similar but are very different. The reverse charge is used on cross-border services and domestic construction. It does not change the underlying VAT amount; it changes who reports it on the VAT return. The two come up together because both involve VAT and a "reverse" word, but they solve different problems.
What if my gross figure already excludes VAT?
Then it is the net figure, not the gross. Reverse VAT only applies to VAT-inclusive amounts.
If the receipt or quote is marked "ex VAT" or "+ VAT", use the Add VAT calculation instead: gross = net × (1 + rate ÷ 100). Always check whether a quote is inclusive or exclusive before doing arithmetic — confusing the two is one of the most common pricing mistakes on small-business invoices.
How accurate should the VAT figure be?
Round to the nearest penny on each line. Be consistent within a document.
Most jurisdictions accept either line-level or invoice-level rounding, but be consistent within a document. Compound rounding errors on long invoices can leave the gross total a penny off the calculated sum. Always rebuild the gross from the rounded net plus rounded VAT, not the other way around. Accounting software handles this automatically.
Why does my gross divided by 6 not equal the invoice's VAT?
Usually because the invoice contains mixed rates — for example some lines at 20% and some at 0% (food, books, children's clothes).
Apply the fraction to each line at its own rate, not to the invoice total. Less commonly: the invoice uses a different rate, a margin scheme, or a partial exemption calculation. Check the invoice carefully before assuming the math is wrong. A 1p discrepancy is usually rounding, not a real error.
Can I use reverse VAT to check a competitor's price?
Yes — knowing the net price tells you the supplier's true selling price before tax.
A B2B competitor advertising £600 gross sells at £500 net at 20% VAT. If you sell the same item at £550 net, your gross is £660 — £60 dearer at the till. Reverse VAT is a quick tool for competitive pricing analysis. Just confirm the rate matches: UK consumer prices include VAT; many B2B quotes do not.
Is reverse VAT relevant for petty cash?
Yes. Apply the VAT fraction to expense receipts to extract the input VAT for the Box 4 entry on your VAT return.
Standard rate receipts use 1/6; reduced-rate energy uses 1/21; zero-rated food has nothing to reclaim. Without a VAT number on the receipt, you cannot reclaim — keep this in mind when authorising staff expenses. Receipt photographs in expense apps still need the VAT number visible to qualify.
Sources and references
- HMRC VAT Notice 700 — The VAT Guide
- gov.uk — VAT rates on different goods and services
- HMRC — VAT invoices and records