To calculate sales tax on a calculator, multiply the item’s price by the tax rate expressed as a decimal, then add that result to the original price. The whole process takes about five seconds once you know the keystrokes. Here’s exactly how to do it, plus shortcuts for calculators with built-in tax buttons.
The Basic Formula
Every sales tax calculation follows the same three steps:
- Convert the tax rate to a decimal. Divide the percentage by 100. A 7% tax rate becomes 0.07. An 8.25% rate becomes 0.0825.
- Multiply the price by the decimal. This gives you the dollar amount of tax.
- Add the tax to the original price. This is your total cost.
Written as a formula: (tax rate ÷ 100) × price = tax amount. Then: price + tax amount = total.
Step-by-Step on a Standard Calculator
Say you’re buying a pair of shoes for $85 and your local sales tax rate is 8.5%. Here’s exactly what you press:
- Key in 85 × 0.085 =
- The screen shows 7.225, which is the tax. Rounded to the nearest cent, that’s $7.23.
- Now press + 85 = to get the total: $92.23.
If you want to skip a step, there’s a one-line shortcut. Instead of calculating the tax separately and adding it, multiply the price by 1 plus the decimal tax rate. For 8.5% tax, that means typing 85 × 1.085 =, which gives you $92.225 (round to $92.23) in one shot. The “1” represents the full price, and the “.085” represents the tax, so you get both at once.
How to Find Your Total Tax Rate
Your sales tax rate is rarely just one number from one source. Most areas combine a state rate with a local rate set by your city, county, or special district. You need the combined total for an accurate calculation. For example, a state might charge 5.5%, and your city might add another 1.5%, giving you a combined rate of 7%.
The easiest way to find your exact combined rate is to search your state’s department of revenue website for local sales tax rates, or look at a recent receipt from a store in your area. The rate printed on the receipt is the total combined rate you should use in your calculations.
Calculating the Price Before Tax
Sometimes you know the total you paid but need to figure out what the item cost before tax. This comes up when splitting receipts, filing expense reports, or checking that a store charged you correctly. The formula works in reverse: divide the total by 1 plus the decimal tax rate.
For example, if you paid $53.50 total and the tax rate is 7%, press 53.50 ÷ 1.07 = on your calculator. The result is $50, which is the pre-tax price. To double-check, you can multiply $50 × 0.07 to get $3.50 in tax, and $50 + $3.50 = $53.50.
Using the TAX+ Button on a Desktop Calculator
Many desktop and office calculators from brands like Casio and Sharp have dedicated TAX+ and TAX- buttons. Once you program your local rate, these buttons add or remove tax with a single press, so you don’t have to remember the decimal conversion each time.
To set the rate on most Casio models, press AC, then hold the % key for about two seconds until the display changes. Key in your tax rate (for example, 8.25), then press % again to save it. After that, you can type any price and hit TAX+ to instantly see the total with tax included. Pressing TAX- on a total will strip the tax off and show you the pre-tax price.
To verify what rate is currently stored, press AC and then TAX+. The display will show the saved percentage. If you move to an area with a different rate, just repeat the programming steps with the new number.
Calculating Tax on Multiple Items
When you’re buying several things at the same tax rate, add up all the prices first, then apply the tax to the subtotal. This matches how stores actually calculate your receipt and avoids small rounding differences that can happen when you tax each item individually.
On your calculator, key in each price separated by the + sign: 12.99 + 24.50 + 8.75 = to get a subtotal of $46.24. Then multiply that subtotal by 1 plus your tax rate. At 6% tax: 46.24 × 1.06 = $49.01 (rounded).
Quick Reference for Common Tax Rates
To save time, here are the multipliers for rates you’ll encounter most often. Just multiply the price by this number to get the total including tax:
- 5% → multiply by 1.05
- 6% → multiply by 1.06
- 6.5% → multiply by 1.065
- 7% → multiply by 1.07
- 7.5% → multiply by 1.075
- 8% → multiply by 1.08
- 8.25% → multiply by 1.0825
- 8.5% → multiply by 1.085
- 9% → multiply by 1.09
- 9.5% → multiply by 1.095
- 10% → multiply by 1.10
If your rate isn’t listed, just take the percentage, move the decimal point two places to the left, and add 1. A rate of 7.75% becomes 1.0775.
Using the Phone Calculator
The calculator app on your phone works the same way as a basic handheld. Type the price, tap the multiplication sign, enter 1 plus your decimal rate, and tap equals. On an iPhone, turning the phone sideways switches to a scientific calculator, but you don’t need any of those extra functions for sales tax. The standard view handles everything.
For even faster results, you can ask your phone’s voice assistant to do the math. Saying “What is $85 plus 8.5% tax?” will return the correct total without opening any app at all.