How to Calculate Discounts: Sale Price, Double Discounts and Tax

 

To calculate a discounted price, multiply the original price by the percentage remaining after the discount. For successive discounts, apply each reduction to the remaining price rather than adding the percentages.

Sale price = original price x (1 - discount percentage / 100)

Use our Discount Calculator for up to three successive discounts and optional tax on the discounted subtotal.

Single discount example

A $100 item with 20% off costs $100 x 0.80 = $80 before tax. The savings are $20.

For a 7.5% discount, the remaining-price factor is 1 - 0.075 = 0.925. A $100 item therefore costs $92.50 before tax. In a field labeled discount percentage, enter 7.5, not 0.075.

Why 20% plus 10% is not 30% off

With successive discounts, the second rate applies to the reduced price.

1. Start with $100.
2. Take 20% off: $100 - $20 = $80.
3. Take 10% off the remaining $80: $80 - $8 = $72.

Total savings are $28, giving an effective combined discount of 28%, not 30%.

Combined discount = 1 - (1 - first rate) x (1 - second rate), with rates expressed as decimals. For this example, 1 - 0.80 x 0.90 = 0.28.

Triple discount example

Add a 5% reduction to the previous example:

$100 x 0.80 x 0.90 x 0.95 = $68.40

The combined discount from the rates is 31.6%, not 35%. If a promotion defines discounts differently, follow its terms rather than assuming they stack.

Add tax after discounts

For the $72 discounted subtotal, an entered tax rate of 8% gives:

Tax = $72 x 0.08 = $5.76

Final total = $72 + $5.76 = $77.76

This is the calculator's tax model. It does not determine the legal taxable amount. Coupon, rebate, product, and location rules can differ. Confirm the applicable rules and your seller's receipt.

How to calculate savings

Savings before tax = original price - discounted subtotal.

Comparing an original pre-tax price with a final after-tax amount mixes two different measures. Keep tax separate when comparing the value of a discount.

Understand the rounding rule

Our calculator rounds the subtotal to cents after each discount, rounding half a cent up. It then calculates tax on the rounded discounted subtotal and rounds that tax once.

The combined percentage is derived from the rates before monetary rounding. On very small prices, cent rounding can make the realized savings percentage differ from that rate-based percentage.

Without rounding, changing the order of the same percentage discounts does not change the final result. With per-step rounding, small amounts can differ. Enter the order used by your seller.

Common mistakes

• Adding successive discount percentages instead of multiplying remaining-price factors.
• Entering a decimal fraction in a field that expects a percentage.
• Assuming a fixed-dollar coupon works like a percentage discount.
• Applying tax to the wrong base for the rules of the purchase.
• Assuming every advertised promotion can be combined.

Frequently asked questions

What is 25% off $80?

The discount is $20, leaving $60 before tax.

What is 50% off, followed by another 50% off?

The remaining-price factor is 0.5 x 0.5 = 0.25, so the combined discount is 75%, not 100%.

Can I use a dollar coupon in this calculator?

No. This version supports percentage discounts only. Fixed-dollar coupons, rebates, minimum-purchase rules, and shipping require separate calculations.

Does blank tax mean a tax-free purchase?

No. It means no tax was entered in the estimate. It does not establish tax exemption.

Calculate your discounted total

Enter the price, successive percentages, and optional tax in the Discount Calculator. Review the promotion terms and final checkout amount.

This guide provides general arithmetic examples, not tax advice or a seller's final quote.