How to Calculate Percent Change: A Complete Guide for Students and Professionals

Table of contents

The Core Formula: How to Calculate Percent Change
Everyday Example: How to Calculate Percent of Change
How to Calculate Percent Change in Excel
How to Calculate Percent Change Between Two Numbers
How to Calculate Percent Weight Change
How to Calculate Percent Change in Mass
Online Tools: Percent Change Calculators
Why Percent Change Is Important
Common Mistakes When Calculating Percent Change
Practice Problems: Try It Yourself
Conclusion

From economics and science to personal fitness and everyday shopping, percent change shows up everywhere. It's the universal way to compare how much something has increased or decreased over time. If you want to understand trends, track progress, or spot declines, you need to know how to calculate percent change.

Percent change is not just a classroom exercise. Businesses use it to measure sales growth, scientists use it in experiments, and people use it to calculate discounts or weight loss. Without this skill, data comparisons can be misleading.

If you'd like to practice quick calculations, try using a Basic Calculator. For a more detailed background, you can also check resources like Investopedia's guide to percentage change and Khan Academy's lesson on percent change. These provide examples that make the math more approachable.

This guide will walk through everything you need: the basic formula, how to calculate percent change in Excel, how to calculate percent change between two numbers, and even special cases like percent weight change and percent change in mass. We'll also highlight common mistakes and introduce tools like a percent change calculator to simplify the process.

The Core Formula: How to Calculate Percent Change

The essential formula for how to calculate percent change is:

Percent Change = ((New Value - Old Value) ÷ Old Value) × 100

This works for both increases and decreases.

If the result is positive, it shows a percentage increase.
If the result is negative, it shows a percentage decrease.

Example: Basic Increase

Old Value = 50

New Value = 75

((75 - 50) ÷ 50) × 100 = (25 ÷ 50) × 100 = 50% increase

This tells us the new value is 50% higher than the old one.

Everyday Example: How to Calculate Percent of Change

When people ask how to calculate percent of change, they usually mean the same thing. A common scenario is retail discounts.

Example: Sale Price

Old Price = 120

New Price = 90

((90 - 120) ÷ 120) × 100 = (-30 ÷ 120) × 100 = -25%

That means the item is 25% cheaper than before. Knowing how to calculate a percent change like this helps you quickly figure out if a discount is worth it.

How to Calculate Percent Change in Excel

For larger sets of numbers, spreadsheets save time. Here's how to calculate percent change in Excel:

Enter the old value in cell A1.
Enter the new value in cell B1.

In cell C1, type:

=(B1-A1)/A1

Format cell C1 as a percentage.

This formula can be dragged down for multiple rows of data, making Excel ideal for tracking sales, grades, or scientific measurements. If you prefer a pre-built solution, try a percent change calculator Excel template.

How to Calculate Percent Change Between Two Numbers

Sometimes you want to see the change between two values, like test results or sales figures.

Example: Test Scores

Old Score = 70

New Score = 84

((84 - 70) ÷ 70) × 100 = (14 ÷ 70) × 100 = 20% increase

So the new score is 20% higher than the old one. This is the basic method for how to calculate percent change between two numbers.

How to Calculate Percent Weight Change

In health and fitness, you'll often hear about percent weight change. It's a way to measure progress in weight loss or gain.

Example: Weight Loss

Old Weight = 180 lbs

New Weight = 165 lbs

((165 - 180) ÷ 180) × 100 = (-15 ÷ 180) × 100 = -8.3%

This shows an 8.3% weight loss. Tools like a percent weight change calculator can automate this, but understanding the formula helps you track progress accurately.

How to Calculate Percent Change in Mass

In science experiments, especially chemistry and physics, you may be asked how to calculate percent change in mass.

Example: Evaporation in a Lab

Old Mass = 200 g

New Mass = 180 g

((180 - 200) ÷ 200) × 100 = (-20 ÷ 200) × 100 = -10%

So the mass decreased by 10%. This kind of calculation is common when measuring evaporation, reaction rates, or experimental accuracy.

Online Tools: Percent Change Calculators

If manual math isn't your thing, an online percent change calculator can save time. These tools let you enter old and new values, then instantly see the result.

A percent of change calculator is great for general use.
A percent weight change calculator works well in health contexts.
Some websites offer a percent change calculator formula breakdown so you can see how the answer was derived.
A percent calculator change tool, or percent change calculator Excel template is perfect for students or professionals working with lots of data.

These tools are fast, but remember - they don't replace understanding. Knowing the math helps you double-check and apply it in unexpected situations.

Why Percent Change Is Important

Understanding how to calculate the percent change gives you an edge in many areas:

Finance: Compare investments, sales revenue, or expenses.
Science: Track experimental results and compare outcomes.
Health: Measure progress in weight management or patient recovery.
Education: Evaluate student performance or project improvements.

In short, percent change isn't just math - it's a tool for making informed decisions.

Common Mistakes When Calculating Percent Change

Using the wrong base value - Always divide by the old value, not the new one.
Confusing absolute and percent change - Absolute change is just the difference (new - old). Percent change divides by the old value.
Forgetting to note increase or decrease - Positive = increase, Negative = decrease.
Rounding too early - Round at the end for accuracy.

Avoiding these pitfalls makes your results more reliable.

Practice Problems: Try It Yourself

A book costs $40 last year, $50 this year. What's the percent change?
((50 - 40) ÷ 40) × 100 = (10 ÷ 40) × 100 = 25% increase

2. A student's grade dropped from 88 to 80.

((80 - 88) ÷ 88) × 100 = (-8 ÷ 88) × 100 = -9.1% decrease

3. A runner improved their time from 60 minutes to 54 minutes.

((54 - 60) ÷ 60) × 100 = (-6 ÷ 60) × 100 = -10% improvement (negative because time decreased, but that's good here).

These examples show why context matters when interpreting percent change.

Conclusion

Knowing how to calculate percent change is an essential skill for students, professionals, and everyday life. Whether you're learning how to calculate percent change in Excel, figuring out how to calculate percent of change at the store, or measuring how to calculate percent weight change for health goals, the method is always the same.

Online tools like a percent change calculator or percent of change calculator make the process faster, but learning the math behind them builds confidence. With practice, you'll know instantly whether a change is big, small, positive, or negative.

So next time you're asked how to calculate a percent change or even how to calculate percent change between two numbers, you'll have the formula, the steps, and the confidence to solve it.

Percent change won't just be math - it will be a tool you can use to make smarter decisions in school, work, and life!