Sales Tax Calculator — Add Tax or Extract Tax

The Formula

Adding tax multiplies the base price by (1 + rate). Extracting tax (for businesses who collected a total including tax) divides the total by (1 + rate) to find the pre-tax amount. The tax owed is always Total − Net. This is a fundamental calculation for retail businesses, e-commerce sellers, and anyone who needs to determine the correct sales tax to remit to tax authorities. Getting this math wrong is one of the most common accounting errors new business owners make.

Variable Definitions

How to Use This Calculator

1. 1

   Select "Add Tax" to calculate the total price from a pre-tax price. Use this when setting retail prices or creating invoices.

2. 2

   Select "Extract Tax" to find the pre-tax amount and tax owed when you only know the total collected. Essential for reconciling sales reports and preparing tax filings.

3. 3

   Enter your local combined sales tax rate (state + county + city). You can find your exact rate at your state's department of revenue website or through sales tax lookup tools.

4. 4

   Review the tax amount and effective rate — the Extract mode also shows the tax as a percentage of the total collected, which differs from the stated rate.

Common Applications

• Calculate the total price including sales tax for retail purchases or invoices by adding your local combined tax rate.
• Extract the pre-tax amount and actual tax paid from a gross total for accurate accounting and sales tax filing.
• Determine the correct sales tax to remit when you only know the total amount collected from a customer transaction.

Add Tax calculates the gross from a net price; Extract Tax finds the net from a gross total — two different operations for two different scenarios

Understanding the Concept

The "Extract Tax" mode (also called "back-calculating" sales tax) is critically important for business owners and e-commerce sellers who collect a single price from customers and need to know how much of that collected amount to remit to the state. For example: if you sold an item for $108 with 8% tax, you might instinctively calculate $108 × 8% = $8.64 and think you owe that amount. But that is incorrect — $108 is already the gross tax-inclusive amount. The correct calculation is $108 ÷ 1.08 = $100 (pre-tax revenue), meaning you owe exactly $8 in tax. Over-remitting means you lose profit; under-remitting means you risk penalties and interest from the state. This distinction matters more than most new business owners realize because the error compounds with every transaction. For online sellers operating in multiple states, sales tax compliance became significantly more complex after the 2018 South Dakota v. Wayfair Supreme Court decision, which allowed states to require out-of-state sellers to collect and remit sales tax even without a physical presence in the state.

Frequently Asked Questions

Sources & References