Algebra
Percentage Change Calculator
Calculate % increase or decrease between two values. Find the percentage increase or decrease from an original value to a new value, with reverse calculation support.
Examples:
Formula Reference
Linear Equation
ax + b = c → x = (c−b)/a
Quadratic Formula
x = (−b ± √(b²−4ac)) / 2a
Discriminant
Δ = b² − 4ac
Vertex Form
y = a(x−h)² + k
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Solution Methodology
01
Enter Old & New Values
Provide the original value and the new value.
02
Compute Change
Calculate (New − Old) to determine direction and magnitude.
03
Express as Percentage
Divide by |Old| and multiply by 100 to get the percentage change.
Common Questions
How do you calculate percentage change?
Percentage Change = ((New Value − Old Value) / |Old Value|) × 100%. If the result is positive, it is a percentage increase; if negative, a percentage decrease. Always divide by the original (old) value, not the new one.
How do you find the new value given a percentage change?
New Value = Old Value × (1 + percentage/100). For example, a 25% increase on 80 gives 80 × 1.25 = 100. For a decrease, subtract the fraction: a 20% decrease gives Old × 0.80.