Prices that include tax are convenient for customers and treacherous for calculations. The number on the label includes money the business does not keep, and mixing the inclusive and exclusive figures produces errors that persist for months — in quotes, in invoices, and in the margin you thought you were making.
This guide shows how to add tax to a net price, how to remove it from a gross price, and why the obvious shortcut for the second one is wrong.
Adding and removing tax
Every tax-inclusive price contains three numbers: the net amount, the tax, and the gross amount. Net + tax = gross.
Going from net to gross is multiplication. Going from gross to net is division. Using multiplication in both directions is the error that causes most of the trouble.
The example throughout uses a 20 per cent rate because it divides easily. The method is identical at any rate — 5, 7.5, 15, 21 — and the rules on which goods and services are taxable, and at what rate, vary by country. Confirm the treatment that applies to you locally.
Adding tax to a net price
If the net price is known, tax is simply the rate applied to it.
Net 1,000 at 20 per cent: tax = 1,000 × 0.20 = 200. Gross = 1,200.
The business collects 1,200 and, if registered, accounts for 200 to the tax authority. The 200 was never income. Treating it as revenue overstates sales by a fifth and makes every margin calculation wrong.
Removing tax from a gross price
If the gross price is known, the net price is the gross divided by (1 + rate).
Net = gross / 1.20, and tax = gross - net.
At a gross of 1,200: net = 1,200 / 1.20 = 1,000. Tax = 200.
At a gross of 45: net = 45 / 1.20 = 37.50. Tax = 7.50.
At a gross of 96: net = 96 / 1.20 = 80. Tax = 16.
In each case the tax is 20 per cent of the net figure, which is what the tax authority expects to see. It is not 20 per cent of the gross figure, and that distinction is the whole point.
Why subtracting the rate is wrong
The intuitive method is to take the rate off the gross: 1,200 × 0.80 = 960, so tax of 240.
That is incorrect. The 20 per cent was applied to the net, not to the gross. Subtracting 20 per cent of the gross removes more than the tax that was added, and the difference is not small.
The error compounds. On 1,200 the mistake is 40. On 12,000 it is 400. A business that makes it consistently reports lower net sales than it actually has and understates the tax it owes — the kind of discrepancy that surfaces later in a reconciliation.
The correct divisor is 1 + rate, not 1 - rate: 1.20, not 0.80. The two are not reciprocal, and no amount of careful arithmetic will make them so.
Worked example: 1,200 gross at 20 per cent
A freelancer quotes a day rate of 1,000 net. At 20 per cent, the invoice shows:
- Net: 1,000
- Tax at 20 per cent: 200
- Gross total: 1,200
The client pays 1,200. The freelancer keeps 1,000 of income and holds 200 for the tax authority.
Now suppose the client says their budget is 1,200 including tax and asks what that buys. The net is 1,200 / 1.20 = 1,000, so the answer is one day. Had the freelancer subtracted 20 per cent instead, they would have calculated 960 and concluded that the budget falls short — then either reduced the scope or turned the work down for no reason.
The same arithmetic runs the other way on costs. If a supplier charges 1,200 including tax and the business can recover that tax, the real cost is 1,000. Pricing a job as though the cost were 1,200 overstates it by 20 per cent; pricing it as though the cost were 960 understates it by 4 per cent.
Rates, exemptions and registration
Not everything is taxed at one rate. Reduced rates, zero rates and exemptions apply to different categories in different countries, and some businesses are not registered and therefore do not charge the tax at all.
Three practical points follow. First, find out whether you should be registered; thresholds vary and crossing one carries obligations. Second, do not assume a supplier's price includes tax just because the last one did. Third, when a price is quoted between businesses, establish whether it is net or gross before agreeing it — a 20 per cent misunderstanding on a 10,000 project is 2,000.
Common mistakes
- Subtracting the rate from the gross figure. Divide by 1 + rate instead.
- Applying the rate to a price that already includes it. Adding 20 per cent to a gross price gives a number that is wrong twice over.
- Treating collected tax as revenue. It is a liability, not income, from the moment it is charged.
- Mixing net and gross in one comparison. Two quotes are only comparable on the same basis.
- Forgetting that recovery depends on registration. If you cannot reclaim the tax, the gross cost is your real cost.
- Rounding at the wrong point. Round the final tax figure, not each line, or the invoice total will not reconcile.
Getting it right every time
Use the VAT calculator to convert between net and gross in either direction, and check the result against the invoice total rather than the other way round. When you issue the invoice itself, the invoice generator shows the net amount, the rate and the tax as separate lines, which is what most customers and tax authorities expect to see.
General information: this guide explains common business calculations. It is not accounting, tax or legal advice, and rules vary by country. Confirm decisions with a qualified professional.