Transparent method
The formula
Worked example
Example inputs
How to interpret the result
Whether local sales tax applies before or after a discount is a real jurisdictional difference, not a rounding technicality, and it changes the actual final price paid. Some jurisdictions tax the pre-discount price, others tax the post-discount price, and assuming the wrong order produces a final price that's consistently off.
Before you rely on it
What to check
Confirm whether local tax rules apply tax to the pre-discount or post-discount price before calculating the final expected total.
The common error
Where people go wrong with discount calculator
Assuming sales tax always applies after a discount is subtracted. Some jurisdictions calculate tax before the discount is applied, and using the wrong assumption produces a final price calculation that doesn't match what's actually charged.
Sensitivity evidence
How original price changes the final price after tax
| Original price | Final price after tax | Total savings |
|---|---|---|
| $96 | $77 | $24 |
| $108 | $87 | $27 |
| $120worked example | $96 | $30 |
| $132 | $106 | $33 |
| $144 | $116 | $36 |
Every input, tested
Which input moves the final price after tax most
| Input | Tested from | To | Final price after tax at each end | Swing |
|---|---|---|---|---|
| Original price | $108 | $132 | $87 to $106 | $19 (20%) |
| Discount | 23.0% | 27.0% | $99 to $94 | $5.14 (5.3%) |
| Sales-tax rate | 6.0% | 8.0% | $95 to $97 | $1.80 (1.9%) |
Two variables at once
Final price after tax by original price and discount
| Original price \ Discount | 21.0% | 25.0% | 29.0% |
|---|---|---|---|
| $96 | $81 | $77 | $73 |
| $108 | $91 | $87 | $82 |
| $120 | $101 | $96 | $91 |
| $132 | $112 | $106 | $100 |
| $144 | $122 | $116 | $109 |
Step by step
The worked example, input by input
| Input | Value used |
|---|---|
| Original price | $120 |
| Discount | 25.0% |
| Sales-tax rate | 7.0% |
| Final price after tax | $96 |
| Total savings | $30 |
Where the inputs come from
Original price is the regular price before the sale, discount is the percentage off, and the sales-tax rate is added after the discount in most places. Some stores stack discounts, such as 25% off and an extra 10% off, which multiply rather than add. Coupon and rebate rules differ: a manufacturer coupon may reduce the taxable price in some states and not in others.
When the result stops applying
The regular price may be inflated to make a discount look larger, so compare with other stores and price history. Tax treatment varies by state. Minimum purchase requirements, exclusions and shipping fees can change the effective saving. A sale price does not mean you should buy: only buy what you would buy anyway.
What to compare it with
Work backward from a sale price with the percentage change calculator, add tax with the sales tax and reverse sales tax pages, and compare package sizes on the unit price comparison calculator. The tip calculator handles restaurant bills.
People also ask
Frequently asked questions
How do I calculate a percentage discount?
Multiply the price by the discount as a decimal to find the savings, and subtract it. For 25% off $120, 120 times 0.25 is $30 off, so you pay $90.
Do two discounts add up?
No. They multiply: 20% off followed by 10% off leaves 72% of the price, a 28% total discount, not 30%.
Is tax calculated before or after the discount?
In most places on the discounted price, but store coupons and manufacturer coupons can be treated differently, so check your state's rule.