Percentage Change Calculator

Built and maintained by ToolsBuilt • Last updated: October 11, 2026

Quick Answer

The Percentage Change Calculator calculates relative growth or drop between two numbers, increases or decreases a number by a specific percentage rate, or finds what percent one value is of another. Choose a mode below to view instant results and formulas.

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Calculation Result
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Key Facts & Formula Reference

Formula Summary

  • Percent Change: ((New - Old) / |Old|) × 100
  • Percent Increase: Base + (Base × Rate)
  • Percent Decrease: Base - (Base × Rate)
  • Proportion Ratio: (Part / Total) × 100

Sample Calculations

Calculation Input Values Result
Price Rise $50 → $75 +50% increase
Discount $100 less 20% $80 final price
Test Score 45 out of 50 90% score

How to Use the Percentage Calculator

  1. Choose Your Calculation Mode

    Select Tab 1 to find percentage change between two values, Tab 2 to adjust a number by X%, or Tab 3 to find what percentage X is of Y.

  2. Enter Your Numbers

    Input your starting values, percentages, or proportions into the respective fields.

  3. Review the Formula & Step-by-Step Breakdown

    Click the calculate button to view your result along with the mathematical formula and complete step-by-step breakdown.

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How Do You Calculate Percentage Change Between Two Numbers?

To calculate percentage change between two numbers, subtract the old value from the new value, divide the difference by the absolute value of the old value, and multiply by 100. A positive answer indicates a percentage increase, while a negative answer indicates a percentage decrease.

If you are measuring time intervals between project milestones or financial quarter start dates, try our Date Difference Calculator.

How Do You Increase or Decrease a Number by a Percentage?

To increase or decrease a number by a percentage, calculate the percentage portion (multiply base number by percent rate divided by 100) and then add (for increases) or subtract (for decreases) that portion from the starting number.

When preparing reports or financial summaries, you can quickly analyze word count and reading time using our Word & Character Counter, or clean up text formatting with our Text Case Converter.

Understanding the Reversibility Trap

A +50% increase followed by a -50% decrease does not return you to your original starting number. For example, $100 + 50% = $150. Decreasing $150 by 50% removes $75, resulting in $75.

Frequently Asked Questions

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