Discount Calculator

About Discount Calculator

What you actually pay after a discount — or after several, which is where it stops being obvious. Two discounts do not add up: 20% and then another 10% is 28% off, not 30%, because the second one comes off what is left after the first.

There is room for two percentages and a fixed-amount voucher, applied in that order, which is how a checkout usually applies them. Each step shows the running price, so a promotion that sounds better than it is becomes obvious.

The effective percentage at the end is the number to compare offers with: it collapses whatever chain of deductions was applied into one figure.

Where it helps

• Handles stacked discounts correctly, which is the case people get wrong.
• Shows the price after each step, so an offer can be checked as it is applied.
• Collapses the chain into one effective percentage for comparing offers.
• Takes a fixed-amount voucher as well as percentages.

Limits

• The order matters and is fixed here: percentages first, then the voucher, which is the usual checkout order but not a universal one.
• It does not know about minimum spends, excluded lines or delivery charges.
• Tax interacts with discounts differently in different places; work out the discount first, then the tax.

Frequently asked questions

Why is 20% then 10% not 30%?

The second discount applies to the reduced price, not the original. 20% off 100 is 80; 10% off 80 is 72, which is 28% off in total.

In what order are they applied?

Both percentages first, then the fixed voucher — the order most checkouts use, and the one that gives the smaller saving when a voucher is involved.

Is the tax before or after the discount?

Normally after: the discount reduces the price, and tax is charged on what is actually paid. Work the discount out here, then use the VAT or GST tool.

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