How to Calculate a Price with Tax

This turns a pre-tax price into the price a customer actually pays, and shows the tax on top of it. Multiply the pre-tax price by one plus the rate.

$x$ is the pre-tax price, $r$ is the tax rate in per cent and $y$ is the price with tax. The tax itself is $x \times \dfrac{r}{100}$, which is exactly the gap between the two prices.

Example

With a pre-tax price of 1000 and a rate of 10, $y = 1000 \times 1.1 = 1100$, and the tax is $1000 \times 0.1 = 100$.

Notes

To work backwards from a tax-inclusive price, divide instead of taking a percentage off. At 10% you divide by 1.1, so a price of 1100 with tax was $1100 \div 1.1 = 1000$ before tax. Knocking 10% off instead gives 990, which is wrong: undoing a multiplication takes a division, not a subtraction.

Japan charges a reduced rate of 8% on most food, drink and newspapers, so type 8 rather than 10 for those items.

Real invoices must round the tax to a whole unit of currency, and each seller is free to round down, round up or round to nearest. Your receipt can therefore sit one unit either side of the figure here.