Sales tax calculator

The formula

$$T = x\left(1 + \frac{r}{100}\right)$$ $$x = \frac{T}{1 + r/100}$$

$x$ is the price before tax, $r$ the tax rate in percent and $T$ the total you pay.

Where it comes from

The tax is $r$ percent of the price, $x \cdot r/100$. Adding it to the price and factoring out $x$ gives the multiplier form:

$$T = x + x\cdot\frac{r}{100} = x\left(1 + \frac{r}{100}\right)$$

At 8.25%, every price is multiplied by 1.0825. Going backwards, from a receipt total to the pre-tax price, means dividing by that same multiplier.

Worked example

A $49.99 item at 8.25% tax:

$$T = 49.99 \times 1.0825 = 54.11$$

Backing tax out of a $108.25 total: $108.25 / 1.0825 = 100.00$, so $8.25 of it was tax.

Watch out for

• Don’t subtract the percentage from the total. 8.25% of $108.25 is $8.93, more than the $8.25 of tax actually paid. The tax was a percentage of the smaller, pre-tax number.
• Rates are local. In the US, state, county and city rates stack, so look up the combined rate for the address.

Last checked November 11, 2026