Percentage Calculator — Percent, Increase & Decrease Free
Percentage calculations come up everywhere — discounts, tax, grades, statistics, growth rates, tips, and data analysis. Our Percentage Calculator solves the three most common percentage problems: "what is X% of Y?", "X is what percent of Y?", and "what is the percentage change from X to Y?"
What Is a Percentage Calculator?
A percentage calculator solves percentage-related math problems. It handles three common question types: finding a percentage of a number, finding what percentage one number is of another, and calculating the percentage increase or decrease between two values.
How to Use Our Percentage Calculator
- Choose the type of calculation: percentage of a number, percentage one number is of another, or percentage change.
- Enter the relevant values.
- The result appears instantly with the formula shown for learning purposes.
- Use the calculator for as many problems as you need — no limits.
Why Use an Online Percentage Calculator?
- Three calculators in one: Handles all common percentage problem types without switching tools.
- Shows the formula: Learn how the calculation works while getting the answer.
- Instant and accurate: No rounding errors from mental math or quick phone calculator attempts.
- Works with any numbers: Handles decimals, large numbers, and negative values correctly.
Common Use Cases
Shoppers calculate the final price after a discount — 30% off a $79 item is $55.30. Knowing the exact number prevents overspending and helps compare deals across different stores and discount levels.
Students calculate grades — if you scored 42 out of 50 on a test, that is 84%. If you need 90% overall and have 85% so far, the calculator helps determine what score you need on the final exam.
Business analysts calculate growth rates — if revenue went from $1.2M to $1.5M, that is a 25% increase. Year-over-year percentage changes are the most common metric in business reporting.
Tips and Best Practices
- Percentage increase and decrease are not symmetric. A 50% increase followed by a 50% decrease does not return to the original number — it ends up 25% lower.
- For quick mental math: 10% is easy (move the decimal point), and you can build other percentages from it. 15% = 10% + half of 10%.
- When comparing percentages, consider the base numbers. A 100% increase from $10 ($10 gain) is much less impressive than a 10% increase from $10,000 ($1,000 gain).
Ready to try it? Use our free Percentage Calculator now — no signup required, works entirely in your browser.
Frequently Asked Questions
How do I calculate a percentage of a number?
Multiply the number by the percentage and divide by 100. For example, 20% of 150 is (150 × 20) / 100 = 30. Our calculator handles all three common percentage problem types.
How do I calculate percentage increase?
Percentage increase = ((New Value - Old Value) / Old Value) × 100. For example, if a price went from $80 to $100, the increase is ((100-80)/80) × 100 = 25%.
Is a 50% decrease followed by a 50% increase the same?
No. A 50% decrease from 100 gives 50. A 50% increase from 50 gives 75 — not back to 100. Percentage changes are not symmetric because they are calculated on different base values.