Discount calculator

How to use the discount calculator

1. Type the original price, without the currency sign.
2. Type the discount: 25 for 25% off.
3. For a second discount on top, like “an extra 10% off sale prices”, type it in Extra discount.

The final price, what you save and the total discount show as you type, with the working under them, so you can check each step.

The formula

To take a percentage off a price, multiply by what’s left:

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

25% off means you pay 75%, so you multiply by 0.75. Here is what common discounts do to 80.00:

Discount	Multiply by	80.00 becomes
10% off	0.9	72.00
20% off	0.8	64.00
25% off	0.75	60.00
30% off	0.7	56.00
50% off	0.5	40.00

Two discounts don’t add up

When a shop offers “an extra 10% off sale prices”, the 10% comes off the sale price, not the original one. So 20% off and then 10% off isn’t 30% off:

• 100 with 20% off is 80.
• 80 with 10% off is 72.
• You save 28: that’s 28% off, not 30%.

The quick way: multiply what you pay each time. 80% × 90% = 72% of the price, so 28% off. Two discounts of 50% leave a quarter of the price: 75% off, not free.

A worked example

A jacket costs 80.00, with 30% off. Type 80 and 30:

• 80.00 × (1 − 30 ÷ 100) = 56.00, and you save 24.00.

At the till, there’s an extra 10% off sale prices. Type 10 in Extra discount:

• 56.00 × (1 − 10 ÷ 100) = 50.40.
• You save 80.00 − 50.40 = 29.60: 37% off in all (70% × 90% = 63% of the price), not 40%.

Finding the original price

To go back from a sale price, divide by the part you paid: original = sale price ÷ (1 − discount ÷ 100). You paid 45 with 25% off, so 75% of the price: 45 ÷ 0.75 = 60. The percentage calculator does it too: 45 is 75% of what?

Deals as a percentage

Deals are easier to compare as a percentage. When the items cost the same:

Deal	You pay	Off the total
Buy one, get one half price	1.5 for 2	25%
3 for the price of 2	2 for 3	33.3%
Buy one, get one free	1 for 2	50%

When they don’t, the free or half-price item is usually the cheaper one, so you save less. With items at 40 and 30, the second half price, you pay 55 instead of 70: 21.4% off. And a deal is only a saving if you wanted the second item.

Mental shortcuts

• 10% off: move the decimal point one place to the left and subtract. 10% of 64 is 6.40, so you pay 57.60.
• 20% off: double the 10%. 20% of 64 is 12.80, so you pay 51.20.
• 25% off: take off a quarter. 25% off 48 is 36.
• Think of what you pay: 30% off means paying 70%. 70% of 80 is 56.