% Change = ((New − Old) / |Old|) × 100. Positive = increase, negative = decrease.
From $50 to $75 = +50% increase. From $75 to $50 = -33.3% decrease.
This tool is most valuable when you need a result to compare against something else: a quoted figure, a competing option, or a budget threshold. Accurate comparisons require accurate inputs and arithmetic — this calculator ensures both.
The most frequent error is rounding intermediate values before completing the full calculation. Round only the final result — rounding intermediate steps compounds errors in multi-step calculations, sometimes significantly.
A student checks their overall module grade before results day: 3 assignments scored 72%, 68%, and 81% — the calculator confirms the weighted average and tells them what score they would need on the final exam to achieve a target grade.
% Increase = ((New Value − Old Value) / Old Value) × 100.