Percentage Decrease Calculator
Discount maths with textbook working: % drop between numbers, apply a discount, or reveal the true original price.
💡 Enter marks, prices, followers, weights — any before/after pair.
120 → 80 is a
33.33% decrease
absolute change: -40
Step-by-step working
1. Change = 80 − 120 = -40
2. Divide by the original: -40 ÷ 120 = -0.3333
3. × 100 → 33.33% decrease
📊 Before and after
⚠️ Percentage changes don't cancel: +50% then −50% leaves you at 75% of the start, because the second change acts on a different base. The reverse mode exists precisely for this asymmetry.
📉Discounts, drops, and the original-price trap
Percentage decrease shows up everywhere money and marks do: discounts, depreciation, weight loss, falling scores. This calculator solves all three shapes with the working written out: the decrease between two numbers (120 → 80 = −33.3%), applying a decrease("₹500 minus 15% = ₹425"), and the shopkeeper's favourite trap — finding the original price from the discounted one ("it's ₹690 after 15% off; the tag price wasn't 690 plus 15%").
📊Everything you'd want to know
- Three modes: between two values, apply a decrease, and find-the-original (reverse).
- Textbook-style steps for every answer, ready to copy into homework.
- Before/after bars that make the drop visible.
- A quick discount table from 5% to 100% on your number.
- The asymmetry warning: a 33% drop needs a 50% rise to undo.
🧮The maths
Divide by the original, always. And note the asymmetry with increase: 120 → 80 is a 33.3% decrease, but climbing back 80 → 120 is a 50% increase — same distance, different base.
💡Where you'll use it
- Sale season: reverse mode reveals whether the 'original price' on the tag is honest.
- Depreciation: a phone losing 20% a year is worth 51% of its price after 3 years — decreases compound too.
- For stacked discounts (30% + extra 10%), use our Discount Calculator — they don't simply add to 40%.
- Marks dropped from 90 to 75? That's −16.7% — knowing the size helps plan the recovery honestly.
💡 Frequently Asked Questions
How do I calculate percentage decrease?+
Subtract the new value from the original, divide by the original, multiply by 100: (original − new) ÷ original × 100. From 120 to 80: (40 ÷ 120) × 100 = 33.33% decrease. The calculator writes out these steps for your numbers.
How do I take a percentage off a price?+
Multiply by (1 − percentage ÷ 100): ₹500 with 15% off is 500 × 0.85 = ₹425. The apply mode shows the saving and final price, plus a quick table of common discounts.
How do I find the original price before a discount?+
Divide by (1 − %/100) — never add the percentage back. ₹690 after 15% off was 690 ÷ 0.85 = ₹811.76. Adding 15% to 690 undercounts, because the discount was taken from the larger original.
Why doesn't a 50% decrease cancel a 50% increase?+
Because each change uses a different base: 100 + 50% = 150, then 150 − 50% = 75. Undoing a decrease of d% needs an increase of d ÷ (1 − d/100) percent — a 33.3% drop takes a 50% rise to recover.
Can a percentage decrease exceed 100%?+
Not for quantities that stop at zero (price, marks, weight) — a 100% decrease means it's gone. Values that can go negative (profit, temperature) can fall by more than 100%.