Percentage Decrease
Percentage Decrease - a browser-based calculators utility.
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About Percentage Decrease
Taking a percentage off a figure, or measuring how far something has fallen. The second is where mistakes cluster, because a fall and the rise needed to undo it are not the same percentage and never have been. Free, immediate, and without a sign-in step. Everything is calculated in the page you are looking at.
How to use it
- Take a percentage offA price and a discount gives the new price, and the amount saved alongside it.
- Or measure a fallAn old and a new value gives the percentage drop between them.
- Or recover the originalGiven the reduced figure and the discount applied, work back to what it was before.
Why a 50% fall needs a 100% rise
Percentages are always of something, and after a fall that something is smaller. Drop 100 by half and you have 50; to return to 100 you must add 50, which is the whole of what remains — a 100% rise. This asymmetry is why a portfolio down 50% needs to double rather than gain 50%, and it catches people every time.
What it does not do
- A decrease of more than 100% is not meaningful for a positive quantity — it would take the value below zero, which usually indicates the wrong calculation rather than a real result.
- Successive discounts do not add. Twenty percent off and then a further ten percent off is 28% off, not 30%.
Questions people ask
- How do I find the original price before a discount?
- Divide rather than add back. A price of 80 after 20% off was 80 ÷ 0.8 = 100. Adding 20% back onto 80 produces 96, which is neither the original price nor anything useful.
- Do two discounts add together?
- No. They apply one after the other, so 20% then 10% leaves 0.8 × 0.9 = 0.72 of the original — a 28% reduction rather than 30%.
Questions about ToolsVerse itself — privacy, cost, what happens to your files — are answered in the frequently asked questions.
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