How to Calculate VAT From a Gross or Net Amount

This article first appeared on Invoala.

To calculate VAT you need to know which figure you're starting from. If your amount is net (VAT-exclusive), multiply it by the rate — 20% of 500 is 100, so the gross is 600. If your amount is gross (VAT-inclusive), divide by 1 + the rate instead — 600 ÷ 1.20 = 500 net, and the VAT is the 100 difference. That's the whole trick: dividing by 1.2 undoes a 20% uplift, while multiplying by 1.2 applies one. Everything else on this page is about applying that correctly, handling rounding, and getting it onto an invoice.

Rates differ by country and by what you're selling — standard, reduced and zero rates all exist, and some supplies are exempt entirely. The mechanics below work for any rate; only the number changes. Check your national tax authority's published rate for your specific goods or services rather than trusting a rule of thumb.

The two formulas, and why the second one surprises people

From net to gross: VAT = net × rate, then gross = net + VAT.

From gross to net: net = gross ÷ (1 + rate), then VAT = gross − net.

The second step is where people go wrong. It's tempting to take 20% off a gross figure and call that the VAT — but 20% of a gross amount is not the same as 20% of the net amount it was built from. On 600 gross, 20% would give 120, and 600 − 120 = 480, which is not the correct net figure. The correct net is 500 because the VAT is charged on 500, not on 600.

A useful shortcut: at 20%, the VAT portion of a gross amount is exactly one sixth of it (100 ÷ 600 = 1/6). At 5% it's 1/21 of the gross. You can derive a fraction for any rate with rate ÷ (1 + rate), but the division formula is safer to remember than a set of fractions.

Photo by Kelly Sikkema on Unsplash

Working out the VAT portion only

Sometimes you don't need the net at all — you just need the tax line to put on an invoice. In that case:

At 20%: multiply the gross by 0.2 and divide by 1.2, which is the same as dividing by 6. At 10%: gross × 0.1 ÷ 1.1. At 7.5%: gross × 0.075 ÷ 1.075.

This one-liner is handy when a client pays a flat inclusive sum — a retainer, a package price, a fixed quote — and you need to back out the tax you owe. If you invoice in multiple currencies or across borders, note that the rate that applies is generally set by the customer's location and the nature of the supply, and the rules for cross-border services differ from those for goods. Our guide to sales tax, VAT and GST on invoices walks through which regime typically applies in which situation.

Example: reverse-engineering VAT from a £1,200 gross invoice

Say a client agrees to pay you a flat £1,200 for a project at a 20% VAT rate, and you need to record the net and the VAT separately.

Net: £1,200 ÷ 1.20 = £1,000
VAT: £1,200 − £1,000 = £200 (check: £1,000 × 0.20 = £200 ✓)
Total charged: £1,200

Now the same project quoted the other way round, as a net figure:

Net: £1,000
VAT at 20%: £1,000 × 0.20 = £200
Gross: £1,200

Both routes land in the same place, which is exactly the point — you should be able to move between gross and net without the numbers drifting. If you bill several line items, work out the VAT on the invoice subtotal rather than line by line unless your tax authority requires per-line rates; it keeps rounding cleaner.

Rounding is the one place small discrepancies creep in. If you have three line items of £33.33 each at 20%, the per-line VAT rounds to £6.67 three times (£20.01), while the VAT on the £99.99 subtotal is £20.00. Pick one method, apply it consistently, and be aware that a penny of difference is normal rather than an error. Most accounting software rounds at the invoice level.

Putting the right figures on the invoice

A compliant invoice generally needs to show the net amount, the VAT rate, the VAT amount and the gross total separately — not just a single inclusive figure. In most countries that separation is a legal requirement for a valid tax invoice, and it's what lets your customer reclaim the tax if they're registered. The exact fields, wording and any registration-number requirements depend on your jurisdiction, so check your tax authority's guidance for the format it expects.

For a simple, non-VAT or single-rate invoice, the layout is: describe the work, show the net subtotal, add a VAT line at the stated rate, then the total due. Keep the rate visible next to the VAT figure — "VAT 20%: £200" reads better than a bare number, and it makes the arithmetic checkable by whoever receives it.

If you're also issuing quotes before the work, remember that a quote is not a tax invoice. An estimate can show an indicative VAT figure, but the VAT becomes chargeable when you actually invoice, at the rate in force at that point.

How Invoala helps you get the VAT lines right

Invoala is a free invoice generator that runs in the browser with no sign-up and no watermark on the output. Here's how it maps to what you've just read:

1. Open the free invoice generator and fill in the form — your details, the client's details, and your line items with net amounts.
2. Add VAT as its own line so the net, the rate and the tax amount stay visibly separate, rather than folding tax into the item prices.
3. Check the totals against the formulas above before you download — the arithmetic is yours to verify, and having the lines split makes it a five-second check.
4. Download the finished document as an A4-accurate PDF, ready to send. Nothing is gated behind an account.
5. If you'd rather not build the layout from scratch, the free invoice templates give you a starting structure with the standard net/rate/tax/total blocks already in place.

For anyone invoicing across several clients at once, Invoala also handles the after-sending side: payment tracking shows which invoices are paid, due or overdue, so a VAT figure you've recorded stays tied to an invoice you can see the status of.

One note for solo operators: whether you must charge VAT at all depends on your registration status and your country's threshold rules, not on the size of the invoice. If you're unsure whether a given project is in scope, that's a question for your tax authority or an accountant — the calculator won't tell you, and neither should a blog post.

Quick reference

From	To	Do this
Net	VAT	net × rate
Net	Gross	net × (1 + rate)
Gross	Net	gross ÷ (1 + rate)
Gross	VAT only	gross × rate ÷ (1 + rate)

Swap rate for your actual rate as a decimal (20% → 0.20, 7.5% → 0.075). The formulas hold for any rate; only your country's published figures and scope rules change.

This article is general information, not tax, legal or financial advice. Rules, rates and deadlines vary by country and change over time. Check with your tax authority or a qualified professional before acting on anything here.

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Originally published at How to Calculate VAT From a Gross or Net Amount. More guides at Invoala.