How sales tax is calculated

The basic sales-tax calculation

Sales tax is usually stated as a percentage, but the calculation uses its decimal form. Divide the rate by 100, multiply it by the taxable subtotal, and then add the tax amount to that subtotal.

1. Identify the taxable subtotal.
   This may differ from the full basket if some items are exempt.
2. Convert the rate to a decimal.
   For example, 7.5% becomes 0.075.
3. Multiply to find the tax.
   Taxable subtotal × decimal rate.
4. Add the tax.
   The sum is the amount due, before any other charges.

A one-step shortcut

You can combine the subtotal and tax into one multiplication. Add 1 to the decimal tax rate, then multiply. At 8%, the multiplier is 1.08; at 6.25%, it is 1.0625.

For the $95 example, $95 × 1.08 gives $102.60 directly. The shortcut is useful when you only need the final total. The two-step method is better when you also need to show the tax amount.

How to remove included tax

If the number you have already includes tax, dividing the total by the tax multiplier finds the pre-tax price. Subtracting the tax rate from the total is not correct because the stated rate applies to the smaller pre-tax amount.

More than one tax rate

A receipt can combine state, county, city or special-district rates. When every component applies to the same taxable subtotal, add the rates first. A 4% state rate plus a 2% local rate produces a combined 6% rate.

Do not add rates when they apply to different items or different bases. In that case, calculate each taxable group separately and combine the results.

Discounts, shipping and exempt items

The arithmetic is simple only after you know what is taxable. Rules for coupons, rebates, shipping charges, digital goods, groceries, clothing and services vary by jurisdiction. A store discount often reduces the taxable price, but some manufacturer-funded discounts and fees may be treated differently.

For example, if a $100 item receives a $20 store discount and tax applies to the reduced $80 price, then 7% tax is $5.60 and the total is $85.60. If local rules use another taxable base, the result changes.

Rounding and receipt differences

Currency is commonly rounded to the nearest cent, but systems do not always round at the same stage. One register may calculate tax on each line item and add the rounded amounts. Another may calculate once on the combined taxable subtotal. Those methods can differ by a cent even when the rate is identical.

For planning, keep extra decimal places until the final step. For checking a real receipt, follow the rounding method and taxable categories printed on that receipt.