Sales Tax Calculator

Sales tax calculations run in two directions and people routinely get the second one wrong. Adding tax to a price is easy: multiply by one plus the rate. Extracting tax from a total that already includes it is where the common error lives — subtracting the tax percentage from the total gives the wrong answer, because the percentage was applied to the smaller pre-tax figure, not to the total. This calculator handles both. Enter a net price to get the tax and the gross total, or enter a tax-inclusive total to recover the base price and the tax component. The same arithmetic applies to VAT, GST, and any other percentage levied on a sale, which makes this useful well beyond the United States — the name differs by country, the calculation does not.

How this is calculated

Adding tax: tax = net × rate, and total = net × (1 + rate). Removing tax: net = total ÷ (1 + rate), and tax = total − net.

Worked example at 8.875%. Adding: a $100.00 item incurs $8.88 of tax for a total of $108.88. Removing: a $108.88 total divided by 1.08875 gives $100.00 net and $8.88 tax.

The mistake to avoid is taking 8.875% of $108.88, which gives $9.66 — off by 78 cents, and the error grows with both the rate and the amount. At a 20% VAT rate, taking 20% of a gross figure overstates the tax by a sixth.

Why the reverse calculation trips people up

The percentage is always applied to the pre-tax price. Once tax is included, that price is no longer the number in front of you, so the percentage no longer corresponds to any share of the total you can see.

The shortcut worth remembering: at a 20% rate, the tax is one sixth of the gross, not one fifth. At 10% it is one eleventh. The general form is rate ÷ (1 + rate) of the gross — which is what dividing by (1 + rate) does for you.

Sales tax, VAT and GST are not the same thing

US sales tax is levied once, at the point of retail sale, and is normally quoted separately from the shelf price — the total at the register is higher than the tag. It is set by state and often by county and city too, so the combined rate varies within a single metropolitan area.

VAT and GST are collected at each stage of production with credits along the chain, and in most countries the advertised price already includes them. The consumer-facing arithmetic is identical, but the expectation is reversed: in Europe or Australia the price you see is the price you pay, which is why the reverse calculation is the one that gets used there.

How to use the sales tax calculator

Enter the amount. Either a pre-tax price or a tax-inclusive total, depending on which direction you need.
Enter the tax rate. Use your combined state and local rate for US sales tax, or the applicable VAT or GST rate elsewhere.
Read the matching row. The calculator shows both directions, so pick the one whose input you supplied.

Frequently asked questions

How do I remove sales tax from a total?

Divide the total by (1 + rate). A $108.88 total at 8.875% tax: 108.88 ÷ 1.08875 = $100.00 base price, $8.88 tax.

Why can't I just subtract the tax percentage from the total?

Because the percentage was applied to the smaller pre-tax price, not to the total. Taking 20% off a gross figure removes more than the tax that was added. The correct extraction is rate ÷ (1 + rate) of the gross — at 20% that is one sixth, not one fifth.

Does this work for VAT and GST?

Yes — the arithmetic is identical. The practical difference is that VAT and GST prices are usually advertised inclusive, so you will mostly want the reverse calculation, whereas US sales tax is added at the register and you will mostly want the forward one.

What sales tax rate should I use?

Your combined rate, which stacks state, county and city components. Two addresses a few miles apart can differ by more than a percentage point, and the rate that applies is generally the one where the buyer takes delivery rather than where the seller is based.