Percentages are used everywhere — from comparing prices and calculating salary increases to measuring business growth, discounts, exam results, inflation and financial changes.
However, percentage calculations can become confusing when you need to determine whether a value has increased, decreased, changed, or differs from another value.
The good news is that the calculations are straightforward once you understand which formula to use.
In this guide, you'll learn:
- How to calculate percentage increase
- How to calculate percentage decrease
- How to calculate percentage change
- How to calculate percentage difference
- The difference between percentage change and percentage difference
- How to calculate percentages step by step
- Real-world examples
- Common percentage calculation mistakes
- How to use a percentage calculator
You can also use the OneCalcApp Percentage Calculator to perform these calculations quickly.
What Is a Percentage?
A percentage represents a number as a fraction of 100. The word "percent" means "per hundred".
For example:
- 10% = 10 out of 100
- 25% = 25 out of 100
- 50% = 50 out of 100
- 75% = 75 out of 100
- 100% = the entire amount
The basic percentage formula is:
Example
Suppose you scored 45 marks out of 60.
So your score is 75%.
How to Calculate Percentage Increase
Percentage increase tells you how much a value has increased compared with its original value.
The formula is:
Example 1: Price Increase
Suppose a product originally costs ₹1,000 and its price increases to ₹1,200.
Divide the increase by the original price:
Multiply by 100:
The price increased by 20%.
Percentage Increase Formula
For quick reference:
where Increase = New Value − Original Value. The complete formula is therefore:
How to Calculate Percentage Decrease
Percentage decrease tells you how much a value has fallen compared with its original value.
The formula is:
Example 2: Price Decrease
A laptop originally costs ₹80,000 and its price falls to ₹68,000.
Divide by the original value:
Multiply by 100:
The laptop price decreased by 15%. The same logic drives every discount calculation.
Percentage Increase vs. Percentage Decrease
The main difference is the direction of the change.
| Calculation | Formula |
|---|---|
| Percentage Increase | (New − Original) ÷ Original × 100 |
| Percentage Decrease | (Original − New) ÷ Original × 100 |
The important point is that the original value is normally used as the reference value.
Example
A price changes from ₹500 to ₹600.
₹600 − ₹500 = ₹100
Now consider a change from ₹600 back to ₹500.
₹600 − ₹500 = ₹100
A 20% increase followed by a 16.67% decrease returns you to the same value, because the reference values are different.
How to Calculate Percentage Change
Percentage change is commonly used when comparing an old value with a new value.
Example 3
A company's monthly revenue increases from ₹2,00,000 to ₹2,50,000.
₹2,50,000 − ₹2,00,000 = ₹50,000
Revenue increased by 25%.
How to Calculate Percentage Difference
Percentage difference is different from percentage increase or decrease. It is generally used when comparing two values without treating either one as the original or reference value.
Example 4
Suppose two measurements are Measurement A = 80 and Measurement B = 100.
|80 − 100| = 20
The percentage difference is approximately 22.22%.
Percentage Change vs. Percentage Difference
This is one of the most common sources of confusion.
Percentage Change
Use percentage change when you have a starting value and a new value, such as an old price and a new price:
((New − Old) ÷ Old) × 100
Percentage Difference
Use percentage difference when comparing two values where neither value is necessarily the baseline:
|A − B| ÷ ((A + B) ÷ 2) × 100
Quick comparison
| Situation | Formula |
|---|---|
| Price increased | Percentage Increase |
| Price decreased | Percentage Decrease |
| Old vs. new measurement | Percentage Change |
| Compare two independent values | Percentage Difference |
Percentage of a Number
Sometimes the question isn't about an increase or decrease. Instead you may want to know: what percentage is 30 of 120?
So 30 is 25% of 120.
How to Calculate a Percentage of a Number
To calculate a percentage of a number:
Example
Find 15% of ₹2,000.
So 15% of ₹2,000 = ₹300.
Reverse a Percentage Increase
Suppose a product costs ₹1,200 after a 20% increase. What was its original price?
A 20% increase means the final value represents 100% + 20% = 120%.
The original price was ₹1,000. The same reverse calculation is used when you remove GST from a gross amount.
Reverse a Percentage Decrease
Suppose an item costs ₹850 after a 15% discount. After a 15% decrease, the remaining value is 100% − 15% = 85%.
The original price was ₹1,000.
Why Equal Percentages Don't Cancel
Suppose a stock price is ₹100 and it increases by 20%:
Now it decreases by 20%:
The final value is ₹96, not ₹100. A 20% increase followed by a 20% decrease is not "no change", because the second percentage is calculated from a different base value.
Real-World Percentage Examples
1. Salary Increase
Your salary increases from ₹40,000 to ₹46,000.
₹46,000 − ₹40,000 = ₹6,000
Your salary increased by 15%.
2. Discount
A product costs ₹5,000 and is discounted to ₹4,250.
₹5,000 − ₹4,250 = ₹750
The discount is 15%.
3. Business Growth
A company generated ₹10 lakh in revenue last year and ₹12 lakh this year.
₹12 lakh − ₹10 lakh = ₹2 lakh
Revenue grew by 20%. To convert that revenue into a margin, use the Profit Margin Calculator.
4. Exam Score
A student scored 72 marks out of 90.
The student's percentage is 80%.
5. Electricity Consumption
A household's electricity consumption increases from 400 kWh to 460 kWh.
460 − 400 = 60 kWh
Electricity consumption increased by 15%.
Common Percentage Calculation Mistakes
Mistake 1: Using the new value as the denominator
For percentage increase and decrease, the original value is normally the reference.
- Incorrect: Difference ÷ New Value
- Correct: Difference ÷ Original Value
Mistake 2: Confusing percentage points with percentage change
Suppose an interest rate changes from 5% to 7%. The increase is 7% − 5% = 2 percentage points, but the relative percentage increase is 2 ÷ 5 × 100 = 40%.
- Increase = 2 percentage points
- Relative increase = 40%
These are not the same thing, which matters whenever you compare loan or deposit rates in the financial calculators.
Mistake 3: Assuming equal percentage increases and decreases cancel
A 20% increase followed by a 20% decrease produces a net decrease. Percentages must always be interpreted relative to their appropriate base.
Frequently Asked Questions
How do I calculate percentage increase?
Use ((New Value − Original Value) ÷ Original Value) × 100. For example, if a value increases from 100 to 120, the calculation is (20 ÷ 100) × 100 = 20%.
How do I calculate percentage decrease?
Use ((Original Value − New Value) ÷ Original Value) × 100.
What is the formula for percentage change?
((New Value − Old Value) ÷ Old Value) × 100. A positive result indicates an increase, while a negative result indicates a decrease.
What is the difference between percentage change and percentage difference?
Percentage change uses a defined starting or reference value. Percentage difference compares two values using their average as the reference.
How do I calculate 20% of a number?
Multiply the number by 0.20. For example, 20% of 500 = 500 × 0.20 = 100.
Can a percentage change be negative?
Yes. A negative percentage change generally indicates a decrease. If a value changes from 500 to 450, then (450 − 500) ÷ 500 × 100 = −10%, so the value decreased by 10%.
How do I calculate the original value after a percentage increase?
Divide the final value by 1 + (percentage increase ÷ 100).
How do I calculate the original value after a percentage decrease?
Divide the final value by 1 − (percentage decrease ÷ 100).
Use a Percentage Calculator
Although percentage formulas are simple, a calculator saves time when you're working with multiple values or longer calculations. The OneCalcApp Percentage Calculator works out increase, decrease, change and difference from any two values.
Related tools that use the same arithmetic:
- Discount Calculator — sale price, savings and effective discount percentage
- GST Calculator — add or remove tax from a net or gross amount
- Profit Margin Calculator — margin and markup percentages from cost and price
- Financial Calculators — EMI, interest, investment and tax tools
Summary
Percentage calculations become much easier when you identify what you're trying to compare. The most important formulas are:
- Percentage: (Part ÷ Whole) × 100
- Percentage Increase: ((New − Original) ÷ Original) × 100
- Percentage Decrease: ((Original − New) ÷ Original) × 100
- Percentage Change: ((New − Old) ÷ Old) × 100
- Percentage Difference: |A − B| ÷ ((A + B) ÷ 2) × 100
The key is to choose the correct reference value before doing the calculation.