The formula
How to calculate vAT / IVA
VAT in Spain and IVA in Mexico both work the same way arithmetically — a percentage added on top of a net price — but neither country charges a single flat rate. Both apply a general rate to most goods and services, and one or more reduced rates to specific categories. Pick a country above, then pick the rate category that applies, and the calculator uses the correct percentage and currency together.
The tax is a straight percentage of the net amount: multiply the net amount by the rate to get the tax, then add the two together for the gross total. Which rate applies depends on both the country and the category of goods or services — Spain runs a general 21% rate alongside a 10% reduced rate and a 4% super-reduced rate; Mexico runs a general 16% rate alongside an 8% rate in border regions and a 0% zero rate for specific categories such as basic foodstuffs.
What to enter:
- Net amount (before tax)
- Country
- VAT / IVA rate
The result updates on every keystroke. The URL updates too, which makes the filled-in version easy to bookmark or send to someone else.
Some of the fields above will accept figures that seem unusual for your own situation, and that is deliberate: the formula behind vAT / IVA works the same way regardless of scale, so the calculator does not stop you testing a hypothetical scenario a long way from your actual numbers — often the fastest way to see which input the result is most sensitive to.
How to calculate vAT / GST
VAT in the UK, IVA in Spain and Mexico, and GST in Australia, Canada and New Zealand all work the same way arithmetically — a percentage added on top of a net price — but none of these countries charges a single flat rate on everything. Most apply a general rate to most goods and services, and one or more reduced or zero rates to specific categories. Pick a country above, then pick the rate category that applies, and the calculator uses the correct percentage and currency together. The US is not in the list: there is no federal VAT or sales tax in the US at all — sales tax is set state by state (and often city by city on top), so a single national figure would not mean anything.
The tax is a straight percentage of the net amount: multiply the net amount by the rate to get the tax, then add the two together for the gross total. Which rate applies depends on both the country and the category of goods or services. The UK runs a general 20% VAT rate alongside a 5% reduced rate and 0% zero rate; Ireland runs 23% general, 13.5% reduced and 0% zero; Australia's 10% GST is close to flat, with only a 0% GST-free category as the exception; New Zealand's 15% GST works the same way; Canada's GST/HST varies by province, from 5% GST-only in Alberta to 13-15% HST in provinces that have merged it with their provincial sales tax — the three options shown are representative examples, not an exhaustive province-by-province list.
What to enter:
- Net amount (before tax)
- Country
- VAT / GST rate
The result updates on every keystroke. The URL updates too, which makes the filled-in version easy to bookmark or send to someone else.
Some of the fields above will accept figures that seem unusual for your own situation, and that is deliberate: the formula behind vAT / GST works the same way regardless of scale, so the calculator does not stop you testing a hypothetical scenario a long way from your actual numbers — often the fastest way to see which input the result is most sensitive to.
Why vAT / IVA matters
A calculation like this usually gets used at a decision point rather than out of curiosity — comparing two real options, checking a number a lender or adviser has quoted, or working out whether a plan that sounded fine in conversation still holds up once it is written down with actual figures. The maths itself is rarely complicated; what is hard is remembering which figures to use and in what order, which is exactly what a dedicated calculator is for.
Beyond a one-off check, the same calculation is worth revisiting whenever the underlying numbers change — a new interest rate, a change in income, a different term. Because the figures live in the page's own web address, coming back to update just one field and compare the new result against the old one takes seconds rather than starting again from a blank page.
It is also worth being clear about what a single figure like this can and cannot settle on its own. It answers the specific question the formula was built to answer, and nothing more — a favourable vAT / IVA result does not automatically mean a decision is a good one overall, since plenty of other factors that a formula cannot capture, from personal circumstances to how comfortable a commitment feels, usually matter just as much as the arithmetic. Use the number as one solid input among several rather than the whole of the decision.
A calculator like this one is often bookmarked and returned to repeatedly over months rather than used once, particularly for anything tied to an ongoing plan such as a mortgage, a savings goal or an investment being tracked. Because the figures live in the web address rather than only in memory, coming back to the same page with updated numbers is quicker than starting from a blank spreadsheet each time.
Why vAT / GST matters
A calculation like this usually gets used at a decision point rather than out of curiosity — comparing two real options, checking a number a lender or adviser has quoted, or working out whether a plan that sounded fine in conversation still holds up once it is written down with actual figures. The maths itself is rarely complicated; what is hard is remembering which figures to use and in what order, which is exactly what a dedicated calculator is for.
Beyond a one-off check, the same calculation is worth revisiting whenever the underlying numbers change — a new interest rate, a change in income, a different term. Because the figures live in the page's own web address, coming back to update just one field and compare the new result against the old one takes seconds rather than starting again from a blank page.
It is also worth being clear about what a single figure like this can and cannot settle on its own. It answers the specific question the formula was built to answer, and nothing more — a favourable vAT / GST result does not automatically mean a decision is a good one overall, since plenty of other factors that a formula cannot capture, from personal circumstances to how comfortable a commitment feels, usually matter just as much as the arithmetic. Use the number as one solid input among several rather than the whole of the decision.
A calculator like this one is often bookmarked and returned to repeatedly over months rather than used once, particularly for anything tied to an ongoing plan such as a mortgage, a savings goal or an investment being tracked. Because the figures live in the web address rather than only in memory, coming back to the same page with updated numbers is quicker than starting from a blank spreadsheet each time.
Worked example
Here is the calculation with the starting values:
- Net amount (before tax): 100
- Country: GB
- VAT / GST rate: general
That gives:
- Tax amount: 20 £
- Total including tax: 120 £
- Rate applied: 20 %
These figures are only the calculator's own starting values, included so the working is visible rather than hidden inside the tool above. Replace them with your own numbers and the same arithmetic applies — nothing about the method changes, only the inputs feeding it.
Reading the result
The gross total is what a consumer pays at the till; the net amount and the tax amount are what a business needs separately for bookkeeping and for a tax return. If a figure already includes tax and the net amount is what is needed instead, divide by (1 + rate) rather than subtracting the same percentage — subtracting the rate from a gross figure overstates the tax removed.
Where this goes wrong. The most common mistake is assuming the general rate applies to everything — many everyday categories (certain food, books, some housing or energy) fall under a reduced or zero rate instead in most of these countries, and using the wrong rate category produces a wrong total even though the arithmetic itself is correct.
A useful check on any unfamiliar result is to compare it against a rough mental estimate first — round the inputs to convenient numbers and see whether the calculator's answer lands in roughly the same territory. A wildly different figure usually means one of the fields was entered in the wrong unit, most often a percentage typed as a whole number where a decimal was expected, or the reverse.
Yes, in both countries. Spain has reduced rates of 10% and 4% for specific goods and services (certain food, books, some housing). Mexico applies a reduced 8% IVA rate in border regions for many goods and services. This calculator uses each country's general rate; a category-specific rate needs to be applied manually if it differs.
That depends on the specific goods or service, which this calculator does not attempt to classify automatically — check the relevant tax authority's category list (Spain's Agencia Tributaria or Mexico's SAT) for the item in question, then select the matching rate category above.
That depends on the specific goods or service, which this calculator does not attempt to classify automatically — check the relevant tax authority's category list for the item in question (HMRC in the UK, Revenue in Ireland, the ATO in Australia, the CRA in Canada, Inland Revenue in New Zealand, the Agencia Tributaria in Spain, or the SAT in Mexico), then select the matching rate category above.
Because there is no federal VAT, GST or sales tax in the US to select — sales tax is set at state and sometimes city level, ranges from 0% to over 11% depending on location, and does not exist at all in a handful of states. A single "US rate" would be misleading rather than useful, so it is left out of this calculator rather than shown as an inaccurate placeholder.
Because VAT, GST and IVA are always calculated in the local currency. Switching the country selector switches the available rate categories and the currency symbol shown next to the result together, so the figure always reads correctly for the country selected.
The headline figure is tax amount. With 100 net amount (before tax), that comes to 20 £. Change any field and the figure moves with it.
Whenever one of the underlying figures changes — a new interest rate, a different balance, an updated term — since the result only reflects what is currently in the fields. There is no need to keep a separate record of past results; the web address for a filled-in version already carries the figures used to produce it.
Not unless a tax rate or a fee is explicitly one of the inputs above. Where it is not, the figure shown is a gross calculation, and any tax due depends on your personal circumstances and current tax rules, which are worth checking separately.
The arithmetic itself is exact — the calculator applies the formula shown above precisely, with no rounding until the final figure is displayed. The uncertainty, where it exists, is entirely in the inputs: an estimated rate or an approximate balance carries that same approximation through to the result.
Example by country
The same net amount of 100, at each country's general (or first-listed) rate category, in that country's own currency:
| Country | Rate category | Tax | Total |
|---|---|---|---|
| 🇬🇧 UK | General, 20% | £20.00 | £120.00 |
| 🇮🇪 Ireland | General, 23% | €23.00 | €123.00 |
| 🇦🇺 Australia | General, 10% | A$10.00 | A$110.00 |
| 🇨🇦 Canada | GST only, 5% | C$5.00 | C$105.00 |
| 🇳🇿 New Zealand | General, 15% | NZ$15.00 | NZ$115.00 |
| 🇪🇸 Spain | General, 21% | €21.00 | €121.00 |
| 🇲🇽 Mexico | General, 16% | MX$16.00 | MX$116.00 |
The general rate is the highest most of these countries charge — Canada's other categories run to 13-15% in provinces that use HST, so the C$5.00 shown here is the lowest end of that range, not a typical figure for the whole country. Switching the rate category in the calculator above shows the reduced and zero-rated equivalents for whichever country is selected.