Percentage Increase Calculator

1. Find % change between two values. Enter the original and new values. The calculator shows whether it is an increase or decrease, the exact percentage, and the absolute difference. For example: from 200 to 250 is a 25% increase. From 250 to 200 is a 20% decrease (note the asymmetry).
2. Find a new value after a % change. Enter a starting value and a percentage. The calculator shows both the increased and decreased results simultaneously. Enter 500 and 15% to see both 575 (after 15% increase) and 425 (after 15% decrease).
3. Find the original value. If you know the final value and what percentage was applied, work backwards to find the starting point. A price of $460 after a 15% increase means the original was $460 / 1.15 = $400.

Watch out for a common mistake: a 50% increase followed by a 50% decrease does not return to the original. 100 × 1.5 × 0.5 = 75, not 100. The percentage decrease needed to undo an increase is always smaller than the original increase.

Percentage increase/decrease:
  % change = ((New - Old) / |Old|) × 100
  Positive result = increase, negative = decrease

  Example: Old = 200, New = 250
  % change = ((250-200)/200) × 100 = (50/200) × 100 = 25%

  Example: Old = 250, New = 200
  % change = ((200-250)/250) × 100 = (-50/250) × 100 = -20%

Find new value after % change:
  New = Original × (1 + %/100)   [for increase]
  New = Original × (1 - %/100)   [for decrease]
  Example: 500 × (1 + 0.15) = 575  [15% increase]
           500 × (1 - 0.15) = 425  [15% decrease]

Find original before % change:
  Original = Final / (1 + %/100)   [if % was added]
  Original = Final / (1 - %/100)   [if % was removed]
  Example: $460 / 1.15 = $400 [original before 15% increase]
           $460 / 0.85 = $541.18 [original before 15% decrease]

Percentage point vs percentage:
  Interest rate rises from 3% to 4%:
    Change in percentage points = 1 pp
    Percentage increase = (1/3) × 100 = 33.3%