How to Calculate Discounts and Final Prices

A discount percentage is a decrease applied to a price. On Percent Folio, Price after first discount = Original Price × (1 − First Discount / 100). If a second discount is enabled, that factor is applied to the already reduced price, not to the original. Optional tax, when used, is calculated after discounts. The discount calculator itemizes each of those amounts. It does not look up live product prices and it does not claim to match every location’s tax rules.

Original price

Enter a price of zero or greater. The tool does not convert currencies. USD, EUR, and GBP only change the symbol in front of the displayed number. A price of 100 labeled EUR is still 100 units in the arithmetic.

Discount percentage

Rates are 0% through 100%. 0% leaves the original. 100% reduces that stage to zero. Rates above 100% are rejected here because this is an ordinary price-reduction calculator, not a rebate model that pays the buyer.

Discount amount

The first discount amount is original minus the price after the first discount. For a 20% discount on 100:

After first = 100 × (1 − 20/100) = 80
First discount amount = 100 − 80 = 20

That 20 is 20% of 100. The second discount amount, if used, is 10% of 80, not 10% of 100.

Price after discount

After one 30% discount on 100, the price is 70. That is example 9 on the examples page. Copy the breakdown if you need the line items in one string. Display of money rounds to two decimal places at the end. Intermediate factors are not rounded to cents and then reused, which would compound display rounding.

Two sequential discounts

Enable the second discount. 20% then 10% on 100:

After first = 80
After second = 80 × (1 − 10/100) = 72
Second discount amount = 8
Total savings before tax = 28

If you had added 20 and 10 and taken 30% of 100, you would have 70. That is the usual adding error. Sequential discounts multiply remaining factors: 0.80 × 0.90 = 0.72.

Why discount rates should not simply be added

Each rate refers to a different base. The first 20% refers to the ticket price. The second 10% refers to whatever is left. Adding the percents pretends both rates still see the original 100. They do not. Stacking more discounts continues the same pattern: always multiply by (1 − next rate / 100).

Optional sales tax

If a tax rate is entered and enabled, Tax = Discounted Price × (Tax Rate / 100), and Final Price = Discounted Price + Tax. On 72 with an 8% tax:

Tax = 72 × 0.08 = 5.76
Final = 72 + 5.76 = 77.76

Tax in this tool is after discounts. Some receipts tax first, or tax only part of a basket, or round each line. Those rules are not modeled. The tax input is limited to 0–30% as a bound for this general calculator, not as a legal maximum.

Rounding to cents

Calculation uses full available JavaScript Number precision. The ledger then shows two decimal places. A stored decimal-place preference for other tools (0–6 places, key pf-decimals) does not override money’s two-place display. Actual checkout totals may still differ because a retailer might round the discount, the tax, or both at different stages.

Common shopping calculation mistakes

Adding stacked percents, taxing the original instead of the discounted price in a “tax after discount” situation, and treating a 20% discount as “subtract 20” regardless of the price are the usual ones. Another is reversing a discount by adding the same percent back: 80 increased by 20% is 96, not 100. Recovering a ticket price from a sale price is a reverse decrease; see reverse percentages.

Related: the plain decrease calculator if you only need one rate and no currency ledger.

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