Discount Calculator

How this is worked out

A discount multiplies the price rather than subtracting from it. Twenty-five per cent off means you pay 75% of the price:

new price = price × (1 − discount ÷ 100)

The part worth understanding is what happens when two discounts stack. They do not add up. The second one applies to the already-reduced price, so it is worth less than it looks:

20% off, then 10% off  →  0.80 × 0.90 = 0.72  →  28% off, not 30%

This is why "extra 10% at the checkout" is a smaller gift than the sign implies, and it is worth knowing before you decide whether a sale is actually good.

The same arithmetic runs the other way. A price cut of 50% needs a 100% rise to get back to where it started.

A worked example

A 120 jacket with 25% off:

• You pay 90
• You save 30

Now add a 10% member discount at the till:

• You pay 81
• You save 39
• Real discount: 32.5%, not the 35% you might expect

The gap is small here — 3 units of currency. On a 2,000 sofa with the same two discounts it is 50, which is worth knowing before you compare shops.

What this doesn't cover

• Where prices already include sales tax or VAT, as they normally do in Europe, leave the tax field at zero. Adding it again inflates the answer.
• Some shops apply the second discount to the original price rather than the reduced one, which works out better for you. The receipt will tell you which happened.
• "Up to 70% off" means the best item in the shop, not the one you want.

Common questions