Percentage Calculator

A percentage calculator handles the three percentage problems people run into every day: finding a percentage of a number, working out what percent one number is of another, and measuring the percent change between two values. Enter your numbers above and each answer appears instantly — no formulas to remember.

What Is a Percentage?

A percentage is simply a way of expressing a number as a fraction of 100. The word comes from the Latin for “per hundred,” so 25% means 25 out of every 100, or one quarter. Percentages are everywhere — discounts and sales tax, tips, test scores, interest rates, statistics, commissions, and growth figures — because they make different quantities easy to compare on a common scale. The trouble is that the same word covers several different calculations, and it’s easy to mix them up or reach for the wrong formula. A percentage calculator removes that friction by laying out the common operations side by side, so you can get a fast, correct answer whether you’re shopping, studying, or running a business.

How to Use This Calculator

1. What is X% of a number? Enter the percent and the number to find the amount — for example, 20% of 150.
2. X is what percent of Y? Enter two numbers to see the first as a percentage of the second — for example, 30 out of 150.
3. Percent change from X to Y? Enter a starting and ending value to see the increase or decrease as a percentage.

Each calculation updates as you type, so you can experiment freely.

The Formulas Behind It

The three calculations use three simple formulas. To find a percentage of a number, divide the percent by 100 and multiply by the number: 20% of 150 is 0.20 × 150 = 30. To find what percent one number is of another, divide the first by the second and multiply by 100: 30 ÷ 150 × 100 = 20%. To find percent change, subtract the old value from the new, divide by the old value, and multiply by 100: from 80 to 100 is (100 − 80) ÷ 80 × 100 = 25%. A positive result is an increase and a negative result is a decrease. Knowing these three patterns covers the overwhelming majority of everyday percentage questions.

Everyday Uses

Percentages show up constantly once you start noticing them. Shoppers use “percent of” to work out a sale price or how much tax or a tip adds. Students and teachers turn marks into “what percent of” to grade tests. Businesses track percent change to measure growth in sales, traffic, or costs from one period to the next, and use “percent of” to calculate commissions, margins, and discounts. Investors read percent change to see how an asset moved. Even everyday news — inflation, poll results, statistics — is reported in percentages. Being able to compute any of these quickly, and to sanity-check a number someone quotes you, is a genuinely useful skill, and this calculator makes it effortless.

Tips and Common Mistakes

• Don’t confuse “percent of” with “percent change” — they answer different questions.
• Percent change is always measured against the starting value, not the ending one.
• A percentage increase then an equal percentage decrease doesn’t return you to the start.
• Be careful with “percent” versus “percentage points” — a rise from 10% to 12% is 2 points but a 20% increase.
• Double-check which number is the whole (the denominator) before dividing.

Mastering Percentages with Confidence

Once the three core calculations make sense, a few mental shortcuts and cautions turn percentages from a chore into something you can do in your head and trust. For quick estimates, remember that 10% of any number is just that number with the decimal point moved one place left, and from there you can build others: 5% is half of 10%, 20% is double it, and 1% is the decimal moved two places. So a 15% tip on a $40 bill is 10% ($4) plus 5% ($2), or $6 — no calculator needed. Reversing a percentage trips many people up: if a price already includes a 25% markup or a 20% tax, you can’t simply subtract that percentage to get the original, because the percentage was taken of the smaller base; instead you divide by 1.25 or 1.20. The same care applies to successive percentages, which don’t add up the way they seem to — a 20% raise followed by a 20% cut leaves you below where you started, because the cut is taken from the higher amount. Watch the language, too. “Percent” and “percentage points” are not the same: a savings rate rising from 2% to 3% is one percentage point, but a 50% increase in the rate, and news headlines often blur the two. When a statistic sounds dramatic, ask what the base is — a “100% increase” in something rare may still be a tiny number, while a small percentage of something huge can be enormous. Used thoughtfully, percentages are one of the most powerful everyday math tools there is, letting you compare prices, judge deals, track growth, and check the claims you’re given. Use this calculator to get instant, accurate answers, and over time you’ll find yourself estimating many of them in your head — and catching the errors that come from applying the wrong percentage rule.

Frequently Asked Questions

How do I find a percentage of a number? Divide the percent by 100 and multiply by the number. For 20% of 150: 0.20 × 150 = 30. The first calculator above does this.

How do I work out what percent one number is of another? Divide the first number by the second and multiply by 100. For 30 of 150: 30 ÷ 150 × 100 = 20%.

How do I calculate percent change? Subtract the old value from the new, divide by the old value, and multiply by 100. A positive answer is an increase, a negative one a decrease.

What’s the difference between percent and percentage points? Percentage points measure the absolute gap between two percentages; percent change measures the relative change. Going from 10% to 12% is 2 points, but a 20% increase.

Why doesn’t a +50% then −50% return to the start? Because each percentage is taken of a different base. 100 up 50% is 150; 150 down 50% is 75, not 100.

This tool is for general calculation only.