Sales Tax Calculator

How This Calculator Works

Sales tax is calculated by multiplying a price by the local tax rate, then adding that amount to the price to get the final total. Enter a price and a sales tax rate, and this calculator handles two everyday questions:

• Add tax to a price — you know the price before tax and want to know the final total (and how much of it is tax).
• Find the price before tax — you’re looking at a receipt or invoice that already includes tax, and want to work backward to the original price and the tax amount.

Sales tax rates vary by state, county, and city, and change over time — this calculator doesn’t guess at a specific rate for you. Enter whatever rate applies where you’re shopping (check your receipt, your state/local revenue department, or a point-of-sale system for the exact rate).

The Formula

Every quantity is color-coded and carried through consistently:

$$\text{Adding tax: } \vC{\text{Tax Amount}} = \vA{\text{Price}} \times \left(\frac{\vB{\text{Rate}}}{100}\right)$$ $$\vD{\text{Total}} = \vA{\text{Price}} + \vC{\text{Tax Amount}}$$

Finding the price before tax rearranges that same relationship backward:

$$\vD{\text{Total}} = \vA{\text{Price}} \times \left(1 + \frac{\vB{\text{Rate}}}{100}\right) \quad\Rightarrow\quad \vA{\text{Price}} = \frac{\vD{\text{Total}}}{1 + (\vB{\text{Rate}} \div 100)}$$

Worked Example

Adding tax: An $80 item at a 7.25% sales tax rate:

1. Tax Amount: $\vA{80} \times \vB{0.0725} = \vC{5.80}$ dollars.
2. Total: $\vA{80} + \vC{5.80} = \vD{85.80}$ dollars.

Finding the price before tax: A receipt shows an $85.80 total at 7.25% tax:

1. Price: $\vD{85.80} \div 1.0725 \approx \vA{80.00}$ dollars.
2. Tax Amount: $\vD{85.80} - \vA{80.00} = \vC{5.80}$ dollars.

Both directions agree, as they should — adding tax to $80 gives $85.80, and working backward from $85.80 gives $80 again.

Common Mistakes

• Assuming one rate applies everywhere. Sales tax varies by state, county, and even city — five states charge no state sales tax at all — so the rate used here should be your own local combined rate, not a national average.
• Applying tax to exempt items. Groceries, prescription medication, and clothing are tax-exempt or taxed at a reduced rate in many states — check your local rules before assuming every purchase is taxed the same way.
• Mixing up the two modes. Adding tax to a pre-tax price and working backward from a tax- included total are the reverse of each other — using the wrong mode for the number you actually have gives a technically-correct but mismatched answer.