Percentage Calculator

Percentage change = ((New Value - Old Value) / |Old Value|) × 100. A positive result indicates an increase; a negative result indicates a decrease. For example, if a stock goes from $50 to $65, the percentage change is ((65 - 50) / 50) × 100 = 30%. This percentage formula works for any two comparable values, whether you are tracking price changes, population growth, or performance improvements.

A percentage increase happens when a value grows larger, while a percentage decrease happens when it shrinks. The key detail many people miss is that the base value changes. For example, a 20% increase from $100 gives $120, but a 20% decrease from $120 brings you back to $96, not $100. This asymmetry is why percentage increase and percentage decrease are not reversible operations. Understanding this is important when evaluating investment gains and losses, discount pricing, or year-over-year growth rates.

Divide the part by the whole and multiply by 100. For example, if you scored 42 out of 60 on a test, your percentage is (42 / 60) × 100 = 70%. This is one of the most commonly used percentage calculations in everyday life — from grading exams to measuring budget utilization. The percentage formula here is straightforward: (part / whole) × 100. Make sure the "whole" is the total or maximum value, not just any reference number, or your result will be misleading.

Differences usually come down to rounding or which value is treated as the base. Some apps round intermediate steps, which can shift the final digit. Others may interpret "X is what percent of Y" differently depending on whether you enter the part first or the whole first. Always double-check which number is your denominator. For the most reliable result, use the exact percentage formula without intermediate rounding — keep full precision until the final step, then round to the desired number of decimal places.

Percentages are everywhere in shopping. A 30% discount on a $80 item means you save $24 (80 × 0.30), paying $56. Sales tax works in reverse: a $56 purchase with 8% tax adds $4.48 (56 × 0.08), bringing the total to $60.48. Many people mistakenly subtract the tax percentage from the discounted price, which underestimates the total. Always apply discounts first, then tax — this is the standard retail order and the one our percentage calculator follows.