How to calculate sales tax from total backwards

Reverse sales tax isn't some something you pay; it's something you calculate. For example, when you're going over your business receipts, you may want to know how much is actual income and how much is sales tax. Instead of calculating sales tax on the purchase amount, you have to figure out sales tax backward and separate it from the total. You can use an online reverse sales tax calculator or figure it out yourself with a reverse sales tax formula.

Collecting Sales Tax

Like income tax, calculating sales tax often isn't as simple as "X amount of money = Y amount of state tax." In Texas, for example, the state imposes a 6.25 percent sales tax as of 2018. However cities, counties, transit authorities and "special tax districts" may together increase the tax by up to 2 percent total. Special tax districts raise money for hospitals, crime prevention, medical services and municipal development, among other causes. Two stores on opposite sides of a street could pay different rates if one of them falls in a special district.

Further muddying the waters, businesses don't charge sales tax on everything. Most states, but not all, exempt groceries; and some states tax services. Some buyers are exempt from paying sales tax, such as schools, libraries and other nonprofits. The result is that you'll have to use a little thought to get your income/sales tax ratio right.

Apply a Reverse Sales Tax Formula 

If you run a retail business with computerized cash registers, they'll be able to break out the total sales tax for you. Otherwise, you'll have to go over your books or handwritten receipts and identify which transactions involved sales tax. Then apply a formula to crunch the numbers. Instead of using a sales-tax calculator, you use what's jokingly called a sales tax "decalculator."

The formula is fairly simple. Divide your sales receipts by 1 plus the sales tax percentage. Multiply the result by the tax rate, and you get the total sales-tax dollars. Subtract that from the receipts to get your non-tax sales revenue.

For example, suppose your sales receipts are $1,100, and the tax is 10 percent. Divide $1,100 by 1.1 and you get $1,000. Multiply that by 10 percent, and you get $100 sales tax, so your non-tax receipts are $1,000. You enter $1,000 in "sales" in your journal and $100 in "sales tax payable."

Use a Reverse Sales Tax Calculator

If you don't want to crunch the numbers yourself, there's no shortage of calculators to do it for you. Just search online for a decalculator or reverse calculator and you'll have plenty of options. You can also find a downloadable Excel decalculator template to save on your computer to handle the job.

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Fraser Sherman has written about every aspect of business: how to start one, how to keep one in the black, the best business structure, the details of financial statements. He's also run a couple of small businesses of his own. He lives in Durham NC with his awesome wife and two wonderful dogs. His website is frasersherman.com

Calculate the original price of an item given the sales tax% and the final price. Evaluate the total sales tax given the starting price and final price. This calculator can also determine the final price after tax and the tax rate given the other two values.

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Reverse Sales Tax Formula

The following formula can be used to calculate the original price of an item given the sales tax % and the final price of the item.

Initial Price=FP/ST/100

  • Where FP is the final price
  • ST is the sales tax (%)

To calculate the initial price of an item using reverse tax, divide the final price of the item by the sales tax rate.

This can be useful for making sure you are being charged the correct amount out at stores, and for understanding the total percent of the final price that is coming from the sales tax.

Reverse Sales Tax Definition

Reverse sales tax is a way to calculate the initial price of an item given the selling price and sales tax.

How to calculate a reverse sales tax

The following example is a step-by-step guide on how to calculate the initial price of an item given its final price and sales tax.

  1. First, you must determine the sales tax % in your state. You can either use Google or look at your receipt to figure this out. The only exception to this is Delaware, which has no sales tax.
  2. Let’ assume the sales tax for this problem is 13%. Quite higher than normal, but it’s just an example.
  3. Now we need to determine the final price of the item. This should be the final number on your receipt if it’s the only item you purchase. If you purchase multiple items, you will need to subtract the others.
  4. Let’s assume the total item was $100.00 to make this problem simple.
  5. Finally, plug the numbers into the calculator or formula above, and you have your initial price. The answer is $88.49.

Use this calculate while shopping to understand the true price of the items you are going to buy or have already bought.