Percentage Calculator: Solve Any Percentage Problem Instantly

Percentages come up constantly — shopping discounts, tax calculations, grade scoring, financial analysis, and data reporting. Yet mental math with percentages is surprisingly error-prone, especially when you need to work backwards or calculate changes. Our Percentage Calculator handles four distinct types of percentage problems so you always get the right answer.

The Four Calculation Modes

Mode 1: What is X% of Y?

The most common percentage question. Enter a percentage and a number, and get the result.

What is 15% of 200?
15 / 100 * 200 = 30

Real-world examples:

• 20% tip on a $85 dinner = $17.00
• 7.5% sales tax on a $499 purchase = $37.43
• 30% discount on a $120 item = $36.00 savings

Mode 2: X is What % of Y?

This mode works in reverse. Given two numbers, it tells you what percentage the first is of the second.

What percent of 80 is 20?
20 / 80 * 100 = 25%

Real-world examples:

• You scored 42 out of 50 on a test = 84%
• 15 out of 200 survey respondents said yes = 7.5%
• Your project used $3,400 of a $10,000 budget = 34%

Mode 3: Percentage Change

Calculate the percentage increase or decrease between two values. This is essential for tracking trends over time.

From 80 to 100:
(100 - 80) / 80 * 100 = +25%

From 100 to 80:
(80 - 100) / 100 * 100 = -20%

Notice that going from 80 to 100 is a 25% increase, but going from 100 to 80 is only a 20% decrease. This asymmetry catches many people off guard because the base number changes.

Real-world examples:

• Revenue grew from $50,000 to $65,000 = +30% increase
• Website traffic dropped from 12,000 to 9,600 visits = -20% decrease
• Stock price moved from $145 to $168 = +15.86% gain

Mode 4: Increase or Decrease by X%

Start with a number and apply a percentage increase or decrease to get the new value.

Increase 200 by 15%:
200 + (200 * 15 / 100) = 230

Decrease 200 by 15%:
200 - (200 * 15 / 100) = 170

Real-world examples:

• A $1,200 rent with a 3% increase = $1,236
• A $60 item after a 25% discount = $45
• A 500-calorie meal reduced by 20% = 400 calories

How to Use Our Percentage Calculator

1. Select the mode that matches your question from the four calculation types
2. Enter your values in the input fields
3. See the result update instantly as you type — no need to click a button
4. Copy the result if you need it elsewhere

Tips

• Switch between modes to approach the same problem from different angles
• The percentage change mode automatically tells you whether the change is positive or negative
• Use increase/decrease mode to quickly calculate sale prices, tax-inclusive totals, or adjusted budgets
• Results display with appropriate decimal precision

Common Percentage Formulas at a Glance

Question	Formula
What is X% of Y?	Y * X / 100
X is what % of Y?	X / Y * 100
% change from A to B	(B - A) / A * 100
Increase Y by X%	Y * (1 + X / 100)
Decrease Y by X%	Y * (1 - X / 100)

Practical Use Cases

Shopping and Discounts

A store advertises “Buy one, get one 50% off” on $40 shirts. Your total is $40 + $20 = $60 for two shirts. What’s the effective discount? Use Mode 2: the $20 discount is what percent of $80 (full price for two)? Answer: 25%.

Finance and Investing

You invested $5,000 and your portfolio is now worth $5,750. Use Mode 3 to find the percentage change: +15%. If you want to project a further 8% gain, switch to Mode 4: $5,750 increased by 8% = $6,210.

Grades and Scoring

You need 70% to pass an exam with 85 questions. Use Mode 1 to find the minimum correct answers: 70% of 85 = 59.5, so you need at least 60 correct answers.

Data Analysis

Last month your website had 8,500 visitors. This month it has 10,200. Use Mode 3 to report the growth: +20% increase in traffic.

Frequently Asked Questions

Why is a 50% increase followed by a 50% decrease not back to the original? Starting at 100, a 50% increase gives you 150. A 50% decrease of 150 gives you 75, not 100. The base changes after the first operation. This is one of the most common percentage misconceptions.

How do I calculate compound percentages? For multiple successive changes, multiply the factors. A 10% increase followed by a 20% increase is 1.10 * 1.20 = 1.32, or a 32% total increase (not 30%).

What is the difference between percentage and percentage points? If an interest rate moves from 3% to 5%, it increased by 2 percentage points but by 66.7% in relative terms. Percentage points measure the absolute difference between two percentages.

How do I reverse-engineer a discounted price? If a discounted price is $75 after a 25% off sale, the original price is $75 / (1 - 0.25) = $75 / 0.75 = $100. Divide by (1 - discount rate) to find the original.

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Try our free Percentage Calculator to solve any percentage problem instantly.