Use this proportional calculation to compare quantities or compute a percentage only after defining the reference, direction, units, and zero-case policy.

Observed value

Required number input.

Accepted value

Required number input.

Calculate absolute percentage error relative to an accepted value. The tool evaluates the supplied inputs together and returns the named outputs below; it does not infer omitted operating conditions or change the units shown.^[1]

Percentage error (%)

The resulting percentage error returned as a number.

• Percentage change is asymmetric, percentage difference uses a chosen denominator, and percentage points are not percentages. Zero or signed baselines and rounded inputs can make familiar formulas undefined or misleading.
• Use finite inputs in the displayed units and preserve more precision than the final presentation requires. Independently verify safety-critical, financial, compliance, or production decisions.

Report the original values and denominator with the result, distinguish relative from absolute change, and retain sufficient precision until final display.

• Percentage Change Calculator

  Calculate signed percentage change from an old value to a new value.

• Percentage Decrease Calculator

  Calculate the percentage decrease from an original value to a smaller value.

• Percentage Increase Calculator

  Calculate the percentage increase from an original value to a larger value.