Discount Calculator

The tool opens on a 100 item at 20% off, and the breakdown updates with every keystroke.

1. Type the Original price, before any reduction.
2. Enter Discount (%), for example 25 for a quarter off. The field accepts 0 to 100.
3. If the shop offers a second reduction, such as an extra 10% at checkout, put it in Extra discount (%) applied after the first. It is taken from the already reduced price, not from the original.
4. Enter Sales tax (%) if you want the amount that will actually be charged. Leave it at 0 where the shelf price already includes tax.
5. Change the Currency symbol if needed.

The large figure, labelled You pay, is the final price. The list shows the original price, each deduction, the Sale price, You save (as an amount and as a percentage of the original), the tax added and the Final price. When two discounts are used, the headline also states that stacked discounts equal a smaller figure than their simple sum.

One discount is sale price = original × (1 - discount / 100). An 80.00 item at 25% off costs 60.00 and saves 20.00. A second discount multiplies, it does not add: after both = original × (1 - d1 / 100) × (1 - d2 / 100). Tax then goes on last, on the reduced price: final = after both × (1 + tax / 100).

With 20% and then 10% on 100.00, the price is 100 × 0.8 × 0.9 = 72.00, so the effective discount is 28%, not 30%. Here is a fuller case: a 120.00 item with 30%, an extra 20% and 8% tax.

The saving and its percentage are measured before tax. Some shops apply a coupon after tax or charge tax on the full price, which gives a slightly different total, so check the receipt against the order used here.

The calculator understands percentage-off offers only. A buy-one-get-one-free deal on two equal items is the same as 50% off their combined price, so enter that total and 50. A fixed coupon, such as 10 off a 40 order, is 25% once you divide 10 by 40, and you can enter that percentage. Offers that depend on spending thresholds or on the cheapest item in a basket need to be worked out by hand first.

Headline percentages are not always what they seem, so compare offers on the amount saved and the final price. Stacked 30% and 20% takes 44% off, not 50%. A large percentage on a cheap item can save less than a small one on an expensive item. To compare two promotions, look at the effective percentage in the You save row, which is the single figure that would give the same price.

To find an original price from a sale price, divide by one minus the discount as a decimal. If an item costs 45 after 25% off, the original was 45 / 0.75 = 60. The calculator has no reverse mode, but you can confirm the result by entering 60 and 25. The percentage calculator covers other percent questions, and the VAT and sales tax calculator adds or removes tax from a price, which is useful when a store quotes tax-inclusive figures.

Sellers choosing a sale price should check what a discount does to their margin with the profit margin calculator, since a 20% cut on price removes far more than 20% of the profit. Figures may differ by a cent or two from a till that rounds each line separately.

One practical habit is to check the total saving as well as the percentage. A deal advertised as up to 50% off often applies to only a few lines, so enter the actual discount shown on the tag for the item you want. If the final price with tax is still above your budget, the calculator makes it easy to test how much extra discount you would need before it fits.