80 after 20% off
- Input
- 80 ÷ 0,8
- Expected output
- 100
The wrong way (80 plus 20%) would give 96.
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original price before the discount, reverse percentage
If a product costs 80 after a 20% discount, the list price was 100, not the 96 that "80 plus 20%" would give. The calculator opens in the "original value" mode, with 80, 20% and the discount direction already filled in, and shows the starting value, the difference and the result of the most common mistake.
The wrong way (80 plus 20%) would give 96.
The wrong way would give 272.09.
The wrong way would give 195.50.
The wrong way would give 1,493.66.
Subtracting 10% would give 990, which is wrong.
Start with 10%, which is the value divided by 10, and build the rest from it: 1% is dividing by 100, 5% is half of 10%, 20% is double 10%, 25% is dividing by 4 and 50% is dividing by 2. For 15% of 80, take 10% (8) plus 5% (4), which is 12. For 35% of 200, add 30% (60) and 5% (10), which is 70. If the numbers are awkward, swap the order: 8% of 50 equals 50% of 8, which is 4.
Divide the price paid by 1 minus the discount as a decimal. For 80 after 20% off: 80 ÷ 0.8 = 100. Do not add 20% of 80, which would give 96.
Because the percent was calculated on the original value, which is larger than the final one. 20% of 100 is 20, but 20% of 80 is only 16, and the difference builds up.
Divide by the markup factor. With a 10% markup, 1,100 ÷ 1.10 = 1,000. Subtracting 10% from 1,100 would give 990, which is not the price before tax.
Undo a discount or increase to find the value from before.
To undo a discount or increase, divide by the factor. Adding or removing the percentage from the final value gives a wrong answer, as the common mistake above shows.
Original = final ÷ (1 − X ÷ 100)
Step by step1 − 20 ÷ 100 = 0.880 ÷ 0.8 = 100100 × 0.8 = 80Calculations run in your browser. No data is sent to a server.