How do you calculate the pre-tax amount from a VAT-inclusive price?

I’m trying to make sure I’m handling VAT-inclusive prices correctly when working backwards to find the original price before VAT.

For example, if an item costs £120 including 20% VAT, my understanding is that you shouldn’t simply subtract 20% from £120. Instead, you divide the VAT-inclusive price by 1.20:

£120 ÷ 1.20 = £100 before VAT

The VAT would therefore be £20.

Is this the standard method you use when working backwards from a VAT-inclusive amount? I’d be interested to hear how others handle this in their bookkeeping or accounting, particularly when dealing with multiple VAT rates.

Yes, that's exactly the right method. Dividing by 1.20 rather than knocking 20% off is the standard approach, and the reason it matters is that the 20% was added to the net figure, not the gross one. Taking 20% off £120 gives you £96, which understates the net and overstates the VAT by £4. Small on one line, but it adds up quickly across a quarter's worth of receipts and will put your VAT return out.

The VAT fraction shortcut
If you only want the VAT element rather than the net, HMRC's VAT fraction is handy. For the standard rate it is 1/6, so £120 × 1/6 = £20. For the reduced rate of 5% the fraction is 1/21. Both give the same result as dividing by 1.20 or 1.05 and then subtracting, just with fewer steps.

Multiple rates
The key thing is to keep each rate on its own line. Never try to blend rates or apply one divisor to a mixed total. So on a supplier invoice with standard-rated goods, reduced-rated items and zero-rated items:

• Standard-rated gross ÷ 1.20
• Reduced-rated gross ÷ 1.05
• Zero-rated and exempt items stay as they are (no VAT to strip out)

If a receipt only shows a single gross total with mixed rates and no breakdown, you'll need the supplier to provide a proper VAT invoice before you reclaim anything. Till receipts from supermarkets usually mark items with a code or asterisk to show which rate applies.

Rounding
Work to at least four decimal places before rounding, then round the final VAT figure. HMRC's guidance (VAT Notice 700, rounding section) allows rounding the total VAT payable on an invoice down to the nearest penny, or to the nearest 0.5p per line. Most bookkeeping software such as Xero, QuickBooks and Sage will handle this automatically if you enter the gross amount and select the rate, so it's worth using that "amounts are tax inclusive" toggle rather than doing the sums by hand.

You can also try our Calculator : https://www.businessforum.uk/blog/business-tools/vat-calculator

AI Helper said:

Yes, that's exactly the right method. Dividing by 1.20 rather than knocking 20% off is the standard approach, and the reason it matters is that the 20% was added to the net figure, not the gross one. Taking 20% off £120 gives you £96, which understates the net and overstates the VAT by £4. Small on one line, but it adds up quickly across a quarter's worth of receipts and will put your VAT return out.

The VAT fraction shortcut
If you only want the VAT element rather than the net, HMRC's VAT fraction is handy. For the standard rate it is 1/6, so £120 × 1/6 = £20. For the reduced rate of 5% the fraction is 1/21. Both give the same result as dividing by 1.20 or 1.05 and then subtracting, just with fewer steps.

Multiple rates
The key thing is to keep each rate on its own line. Never try to blend rates or apply one divisor to a mixed total. So on a supplier invoice with standard-rated goods, reduced-rated items and zero-rated items:

• Standard-rated gross ÷ 1.20
• Reduced-rated gross ÷ 1.05
• Zero-rated and exempt items stay as they are (no VAT to strip out)

If a receipt only shows a single gross total with mixed rates and no breakdown, you'll need the supplier to provide a proper VAT invoice before you reclaim anything. Till receipts from supermarkets usually mark items with a code or asterisk to show which rate applies.

Rounding
Work to at least four decimal places before rounding, then round the final VAT figure. HMRC's guidance (VAT Notice 700, rounding section) allows rounding the total VAT payable on an invoice down to the nearest penny, or to the nearest 0.5p per line. Most bookkeeping software such as Xero, QuickBooks and Sage will handle this automatically if you enter the gross amount and select the rate, so it's worth using that "amounts are tax inclusive" toggle rather than doing the sums by hand.

Click to expand...

for this, although I’m still getting used to using it properly and wanted to make sure I was understanding the calculation correctly.

The 1/6 VAT fraction is useful to know as well. I’ll definitely keep that in mind when checking VAT-inclusive prices.

AI Helper said:

Yes, that's exactly the right method. Dividing by 1.20 rather than knocking 20% off is the standard approach, and the reason it matters is that the 20% was added to the net figure, not the gross one. Taking 20% off £120 gives you £96, which understates the net and overstates the VAT by £4. Small on one line, but it adds up quickly across a quarter's worth of receipts and will put your VAT return out.

The VAT fraction shortcut
If you only want the VAT element rather than the net, HMRC's VAT fraction is handy. For the standard rate it is 1/6, so £120 × 1/6 = £20. For the reduced rate of 5% the fraction is 1/21. Both give the same result as dividing by 1.20 or 1.05 and then subtracting, just with fewer steps.

Multiple rates
The key thing is to keep each rate on its own line. Never try to blend rates or apply one divisor to a mixed total. So on a supplier invoice with standard-rated goods, reduced-rated items and zero-rated items:

• Standard-rated gross ÷ 1.20
• Reduced-rated gross ÷ 1.05
• Zero-rated and exempt items stay as they are (no VAT to strip out)

If a receipt only shows a single gross total with mixed rates and no breakdown, you'll need the supplier to provide a proper VAT invoice before you reclaim anything. Till receipts from supermarkets usually mark items with a code or asterisk to show which rate applies.

Rounding
Work to at least four decimal places before rounding, then round the final VAT figure. HMRC's guidance (VAT Notice 700, rounding section) allows rounding the total VAT payable on an invoice down to the nearest penny, or to the nearest 0.5p per line. Most bookkeeping software such as Xero, QuickBooks and Sage will handle this automatically if you enter the gross amount and select the rate, so it's worth using that "amounts are tax inclusive" toggle rather than doing the sums by hand.

Click to expand...

Thanks, that clears it up. I think I was getting confused because I was looking at the 20% as if it could just be taken off the total.

I’ve mainly been trying to get more comfortable with working backwards from VAT-inclusive prices, so the explanation about the VAT fraction is really helpful. I’ll have to be a bit more careful when there are different VAT rates on the same invoice as well.

That confusion is a really common one, and it catches plenty of people out, including some who've been trading for years. The trick is to remember that the percentage always refers back to the net figure. Once that clicks, the maths falls into place and you'll spot the error immediately when someone else makes it.

A quick sanity check
Whenever you've worked backwards, add the VAT you've calculated back onto the net and see if you land on the original gross. So £100 net + £20 VAT = £120. If you'd used the wrong method, you'd get £96 + £19.20 = £115.20, which doesn't match the receipt, and that mismatch tells you straight away something's off. It takes two seconds and saves a lot of head-scratching later.

It also helps to understand where the 1/6 comes from rather than just memorising it. On a £120 gross, the £20 VAT is 20 parts out of 120, and 20/120 simplifies to 1/6. Same logic for the reduced rate: 5 parts out of 105 gives 1/21. If the rate ever changes again, you can work out the new fraction yourself without waiting for someone to tell you.

Mixed-rate invoices in practice
For invoices with more than one rate, get into the habit of entering them line by line in your software rather than as a single total. Most packages let you set a different VAT code on each line, so a hardware shop receipt with standard-rated tools and a zero-rated book can be recorded accurately in one transaction. If you're ever unsure which rate applies to something, HMRC's VAT rates guidance on GOV.UK lists the categories, and VAT Notice 701 series covers specific goods and services.

The calculator Adam linked further up the thread is worth bookmarking too for quick checks when you're away from your bookkeeping software. Just make sure you pick the "gross to net" option rather than "net to gross", otherwise you'll be adding VAT on top of a figure that already includes it.