Guides/Percent left after a decrease
Percent left after a decrease
“25% off” means you still pay75% of the original. Thinking in “percent left” makes stacked discounts and reverse checks easier.
Rule
- Percent left = 100% − percent decrease
- Pay factor = percent left ÷ 100 (e.g. 0.75)
- New value = original × pay factor —discount math.
Worked examples
- $80 item, 30% off → 70% left → 0.70 × 80 = $56.
- Score drops 15% from 100 → 85% left → 85 points.
- Two decreases: 20% then 10% → left factors 0.80 × 0.90 = 0.72 → 72% left (28% total off) —successive discounts.
Reverse check
If you know the sale price and the percent left, original = sale ÷ (left/100) —original before discount·reverse %.
Common mistakes
- Treating “25% off” as multiply by 0.25 (that yields the discount amount only if applied to the original).
- Assuming +25% then −25% returns to start —± percent round trip.