Percentage decrease calculator

How percentage decrease works

Subtract the new value from the starting value, divide by the starting value, and multiply by 100. From 80 to 60 the drop is 20, and 20 ÷ 80 = 0.25, so it’s a 25% decrease.

Decreases stop at 100%

A positive quantity can lose at most 100% of its value, which takes it to zero. If you get more than 100%, either the values have crossed zero (a profit turning into a loss, for example) or the old and new values are the wrong way round.

Ups and downs don’t cancel

A 25% decrease followed by a 25% increase doesn’t get you back where you started. 80 falls to 60, and 25% of 60 is only 15, so you end at 75. To recover a 25% loss you need a 33.3% gain. The bigger the fall, the larger the gap: a 50% loss needs a 100% gain.

Subtracting a percentage

Multiply by 1 minus the percentage as a decimal. To take 12% off 340, multiply by 0.88 to get 299.20. This is how a percentage discount works, and the discount calculator adds a field for stacking a second discount.

Finding the value before the decrease

If something is worth 63 after a 30% drop, it was worth 63 ÷ 0.7 = 90. Adding 30% to 63 gives 81.90, which is wrong because the 30% was taken from the original, larger value.