How to calculate sales tax and discounts together

Adding sales tax to a price

Sales tax is a percentage of the taxable price, added at checkout. Convert the rate to a decimal by dividing by 100, multiply it by the price to get the tax, then add the tax to the price. A shortcut: multiply the price by 1 plus the decimal rate to go straight to the total.

Example: an item priced at $84.99 in a place with a 7.25% rate. Tax = 84.99 x 0.0725 = $6.161775, which rounds to $6.16. Total = 84.99 + 6.16 = $91.15.

The Sales Tax Calculator works the same way: enter the pre-tax price and the rate and it returns the tax and the total. Its own walkthrough shows $120 at 8.25% producing $9.90 of tax and a $129.90 total.

Use the combined rate for where the sale is sourced. Many places charge a state rate plus county or city rates, and the rates for the buyer's address can differ from the seller's location. The Streamlined Sales Tax Governing Board publishes rate and boundary files that link addresses to the rates for member states, and sellers use them in their tax software. For a one-off purchase, a recent receipt from a nearby store or your state revenue department's website will give you the combined rate.

Working backward: finding the price before tax

Receipts often show only the total. To recover the pre-tax price, divide the total by 1 plus the rate. Do not subtract the tax percentage from the total, because the rate applies to the smaller pre-tax number, not to the total.

Example: you paid $53.46 in a place with 8.25% tax. Pre-tax price = 53.46 / 1.0825 = $49.39. Tax = 53.46 - 49.39 = $4.07. Check it forward: 49.39 x 1.0825 = $53.46.

Now see what the wrong method does. Taking 8.25% off the total gives 53.46 x 0.9175 = $49.05, which is 34 cents too low, and it implies $4.41 of tax when the real figure was $4.07. The error grows with the size of the bill and the rate. On a $107.50 total at 7.5%, the correct pre-tax price is $100.00, while the subtract-the-rate method says $99.44 and overstates the tax at $8.06 instead of $7.50.

The Sales Tax Calculator only works forward from price to total, so use the divide-by-(1 + rate) step yourself when starting from a total.

Stacked discounts do not add up

When a sale price gets a second discount on top, such as a storewide markdown and then a coupon, the second percentage applies to the already-reduced price. That means the percentages multiply, they do not add.

Take 25% off followed by 10% off. The first discount leaves 75% of the price, and the second leaves 90% of that: 0.75 x 0.90 = 0.675. You pay 67.5% of the original, so the combined discount is 32.5%, not 35%. On a $400 item, that is $270 rather than the $260 you would get by wrongly adding the percentages.

The order of percentage discounts does not change the result, since multiplication is commutative. 25% then 10% and 10% then 25% both land on 67.5%. Three discounts work the same way: 20%, 10%, and 5% leave 0.80 x 0.90 x 0.95 = 0.684, a combined discount of 31.6%.

Dollar-amount coupons are different, and the order matters. On a $120 item with 20% off and a $10 coupon, taking the percentage first gives 96 - 10 = $86, while taking the coupon first gives (120 - 10) x 0.80 = $88. The percentage-first order is better for you here because the coupon comes off a smaller number. The Discount Calculator handles percentage discounts only, with one optional second discount; convert a flat coupon to a percentage first (a $15 coupon on an $80 item is 15 / 80 = 18.75%) or subtract it yourself.

Discount first, then tax: a full example

When a store discount lowers the selling price, sales tax is normally figured on the lower price. So the order of operations is: apply the discounts, then add tax to what is left.

Example: a $200 item with 25% off, a further 10% off at checkout, and an 8% sales tax rate. After 25%: 200 x 0.75 = $150. After the extra 10%: 150 x 0.90 = $135. Savings are $65, or 32.5% of $200. Tax = 135 x 0.08 = $10.80. Total = $145.80.

If tax were wrongly figured on the original price, it would be 200 x 0.08 = $16.00 and the total would be $151.00, which is $5.20 too high. The Invoice Total Calculator follows the discount-then-tax order and adds shipping afterward without taxing it. It is a good fit for quotes and invoices where you already have a subtotal.

Be aware of one wrinkle. Some places treat discounts differently depending on who pays for them. A discount the store gives you generally reduces the taxable price, but a coupon that a manufacturer reimburses to the retailer may leave the tax calculated on the pre-coupon amount. Rules differ by state, so check your state revenue department if the exact tax matters. The same goes for shipping, which is taxable in some places and not in others.

Comparing two offers properly

A bigger advertised percentage does not always mean a lower price. Always compare the final price after discounts and tax, not the discount headline.

Example: Store A lists a jacket at $120 with 30% off, which is $84.00. Store B lists a similar jacket at $95 with 10% off, which is $85.50. Store A has the bigger discount and the lower price, but only by $1.50. With 8% tax in both cases, Store A totals $90.72 and Store B totals $92.34.

Stacking helps the same way. The Discount Calculator's own walkthrough takes a $150 jacket at 30% off to $105, then an extra 15% to $89.25. That saves $60.75, or 40.5% of the original price, which is less than the 45% you would get by adding 30 and 15.

Undoing a discount, rounding, and other edge cases

To find the original price from a sale price, divide by the share you paid. If a jacket costs $71.50 after 35% off, the original price was 71.50 / 0.65 = $110.00. This is the reverse of the stacked-discount multiplication: for two discounts, divide by both factors.

Rounding can shift a bill by a cent or two. Say you buy three items at $4.99 each with 6.5% tax. If the register taxes each line, each is 4.99 x 0.065 = $0.32435, which rounds to $0.32, for $0.96 total tax. If it taxes the $14.97 subtotal, tax is $0.97305, which rounds to $0.97. Neither is wrong; stores follow the rounding method their system uses. The EveryFix tools calculate on the whole amount and round the displayed result, so a receipt may differ from them by a cent.

Rate limits in the tools: the Sales Tax Calculator accepts rates from 0% to 25%, the Invoice Total Calculator allows tax up to 30%, and the Discount Calculator accepts discounts up to 100%. Enter 0% for tax-exempt items.

Common mistakes

A few errors cause most of the wrong answers.

• Adding stacked discounts. 25% plus 10% is 32.5% off, not 35%.
• Subtracting the tax rate from a total instead of dividing by 1 plus the rate.
• Taxing the original price when a store discount has already reduced the selling price.
• Using the wrong rate: a state rate alone, or the seller's rate when the buyer's address sets the rate.
• Comparing two sales by the advertised percentage instead of the final price after tax.
• Assuming every item is taxable. Many places exempt some categories, and rules vary by location.

A note on accuracy

These calculations show how the arithmetic works. They are not tax advice. What is taxable, which rate applies, and how discounts, coupons, and shipping are treated vary by state and local jurisdiction. If you collect and remit sales tax for a business, rely on your state revenue department or a qualified accountant for the rules that apply to you.