Sales tax is straightforward to calculate once you know the rate -- and most states post their rates publicly. The trickier calculation is the reverse: you have a receipt total and want to know what the pre-tax price was. Here is how to do both.
Calculating Tax on a Purchase (Forward)
Formula: Tax Amount = Purchase Price x (Tax Rate / 100)
Total with Tax = Purchase Price + Tax Amount
Or more directly: Total = Purchase Price x (1 + Tax Rate / 100)
- $250 item at 8% tax: $250 x 1.08 = $270 total. Tax paid: $20.
- $55 item at 9.5% tax: $55 x 1.095 = $60.23 total. Tax paid: $5.23.
- $1,200 laptop at 7.25% tax: $1,200 x 1.0725 = $1,287 total. Tax paid: $87.
Finding the Pre-Tax Price (Reverse)
If you only have the total and the tax rate:
Pre-Tax Price = Total / (1 + Tax Rate / 100)
- You paid $324 total at 8% tax: $324 / 1.08 = $300 pre-tax. Tax paid: $24.
- Receipt shows $47.85 at 6.5% tax: $47.85 / 1.065 = $44.93 pre-tax. Tax: $2.92.
How State and Local Rates Combine
Your actual sales tax rate is almost always a combination of a state rate plus one or more local rates. They simply add together to form the combined rate you pay.
Example: California state rate 7.25% + Los Angeles County district rate 2.5% = 9.75% combined rate. Apply the combined rate to the purchase price as a single number.
What Gets Taxed and What Doesn't
Sales tax does not apply uniformly to everything. Most states exempt:
- Unprepared groceries (in about 32 states)
- Prescription medications (in most states)
- Some clothing items (Pennsylvania, New Jersey, and others)
Prepared food (restaurant meals, hot takeout) is generally taxable even in states that exempt groceries. Digital goods and services are taxed inconsistently and rules vary by state.
Online Purchases
Since the 2018 Supreme Court ruling in South Dakota v. Wayfair, major online retailers collect sales tax in all states that have one. Smaller retailers may not -- but technically you owe "use tax" on those purchases to your home state regardless, a rule rarely enforced on individuals.
To calculate exactly what you will pay on any purchase, our Sales Tax Calculator adds tax or strips it out in one step.