Discount Calculator

Compare a USD sale price with its original price, apply two discounts in sequence and estimate tax separately.

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How to Use the Discount Calculator

Choose forward calculation from original price or reverse calculation from a before-tax sale price. Enter the first discount and optional additional discount and tax percentages. Blank optional percentages mean zero. Reverse mode uses both entered discounts and does not treat the sale-price input as tax-inclusive.

Formula and Explanation

Remaining-price factor = (1 − discount / 100) × (1 − additional / 100)
Sale price before tax = original × factor
Savings before tax = original − sale price
Effective discount % = (1 − factor) × 100
Tax = sale price × tax % / 100
Amount after tax = sale price + tax
Reverse original = before-tax sale price / factor

The second percentage reduces the already discounted amount. Discounts are not added together. Savings compare the original price with the sale price before tax; tax is shown separately and is applied once to that discounted amount. Calculations retain internal decimal precision and displayed money rounds to cents at the end, rather than rounding each discount stage.

Tax eligibility, coupon restrictions, fees and store-specific rounding are not determined here. The entered tax is a flat percentage applied to the full discounted price. A 100% discount is valid forward but cannot identify a unique original price in reverse mode, even when sale price is zero. Very large reverse results are rejected.

Worked Example

A $100 original price with 20% off followed by another 10% off becomes $100 × 0.80 × 0.90 = $72 before tax. Savings are $28 and the effective discount is 28%. With an illustrative 5% tax, tax is $3.60 and the amount after tax is $75.60. Reverse mode with a $72 sale price and the same discounts returns a $100 original price.

Frequently Asked Questions

Is 20% off plus 10% off the same as 30% off?

No. The second discount applies to the remaining 80%, giving 72% of the original price and an effective 28% discount.

Does total savings include tax?

No. Savings are the original amount minus the discounted amount before tax. The result shows tax and amount after tax separately.

What sale price should I enter in reverse mode?

Enter the price after the discounts but before tax. The original-price estimate reverses both discount factors; the optional tax is then added separately to the sale price.

Why can’t a 100% discount be reversed?

Its remaining-price factor is zero. Any original price would become zero, so the sale amount alone cannot determine a unique original value.