How to calculate sales tax, add it, and back it out of a total

Sales tax in the US depends on the state, county and city, so there’s no single rate. The arithmetic is the same everywhere.

Adding tax

Price × (1 + rate). At 8.25%:

• 50 × 1.0825 = 54.13

By voice: “50 times 1.0825 equals”. Or with the Pro “plus tax” command, set your rate once and say “50 plus tax”.

Backing tax out of a total

This is where people slip. To get the pre-tax price from a total, divide, don’t subtract:

• 54.13 ÷ 1.0825 = 50.00

Subtracting 8.25% from 54.13 gives 49.66. The gap is small on one item and real across a year of expenses.

Just the tax part

Total − (total ÷ 1.0825). For 54.13, that’s 4.13.

Tips

• Check the rate on a receipt from your area. Receipts usually print it.
• For a column of pre-tax prices, add them all first and apply tax once at the end. Fewer steps, fewer rounding differences.
• Some items, like groceries in many states, are taxed at a lower rate or not at all.

More: how to calculate tax by voice.