Percent Calculator

Using a percent calculator is pretty straightforward once you know which type of calculation you need. Most calculators on this page ask you to fill in two known values, and then they solve for the missing one.

• Find a percentage of a number: Enter the percent and the base number. The calculator returns the result.
• Find what percent one number is of another: Enter both numbers. You get the percentage relationship between them.
• Calculate percent increase or decrease: Enter the original value and the new value. The calculator tells you the percent change.
• Find the percentage difference: Enter two values and get the difference expressed as a percent.

Just make sure you're using the right calculator for your situation. Percent increase and percentage difference are not the same thing, and mixing them up gives you a wrong answer every time.

This is the most common percentage question: "What is X% of Y?" You see it on sale tags, recipe conversions, and tax calculations constantly.

The formula is simple:

Result = (Percent / 100) × Number

So if you want to find 30% of 250, you'd calculate (30 / 100) × 250 = 75. That's it.

• 15% of 80 = (15 / 100) × 80 = 12
• 25% of 200 = (25 / 100) × 200 = 50
• 7% of 1,500 = (7 / 100) × 1,500 = 105

A quick mental shortcut: to find 10% of any number, just move the decimal point one place to the left. Then you can build from there. 10% of 340 is 34, so 20% is 68, and 5% is 17.

Sometimes you have two numbers and you want to know how they relate as a percentage. Like, you scored 43 out of 55 on a quiz. What percent is that?

The formula:

Percentage = (Part / Whole) × 100

So 43 ÷ 55 × 100 = about 78.2%.

A few more examples to make it concrete:

• 18 out of 24 = (18 / 24) × 100 = 75%
• 9 out of 36 = (9 / 36) × 100 = 25%
• 52 out of 80 = (52 / 80) × 100 = 65%

This works for any ratio. Revenue compared to a goal, items completed out of a total task list, correct answers on a test — the formula stays the same regardless of context.

Percent change tells you how much something has grown or shrunk relative to where it started. Knowing the direction (up or down) matters, so it's worth distinguishing between increase and decrease rather than lumping them together.

Both calculations start from the same basic idea: compare the difference to the original value, then scale it to a percentage. The sections below walk through each direction separately.

Percentage difference is a slightly different animal than percent change. You use it when comparing two values without treating either one as the definitive "starting point." It's about the gap between them, not a directional shift over time.

You'll see this in scientific data, price comparisons between two stores, or any situation where neither value is clearly the "before" and the other the "after."

Switching between percents, decimals, and fractions is something you'll need to do regularly, especially when plugging numbers into formulas or working with a calculator.

Percent to Decimal: Divide by 100 (or just move the decimal point two places to the left).
45% = 0.45 | 8% = 0.08 | 130% = 1.30

Decimal to Percent: Multiply by 100.
0.72 = 72% | 0.05 = 5% | 1.25 = 125%

Percent to Fraction: Write the percent over 100, then simplify.
50% = 50/100 = 1/2 | 25% = 25/100 = 1/4 | 75% = 75/100 = 3/4

Fraction to Percent: Divide the numerator by the denominator, then multiply by 100.
3/8 = 0.375 × 100 = 37.5%

These conversions are worth memorizing for common values. Knowing that 1/4 is 25% and 1/3 is roughly 33.3% saves real time when you're doing quick mental math.

There are really three core percentage formulas, and they all come from the same relationship between three variables: the part, the whole, and the percent. Know any two, and you can find the third.

These three cover the vast majority of percentage problems you'll encounter. If you're stuck on a percentage question, figure out which of the three variables is missing and apply the right formula.

Here are some worked examples across different scenarios to show how the formulas apply in practice.

1. Sales tax: You buy something for $85 and the tax rate is 6%. Tax = (6 / 100) × 85 = $5.10. Total = $90.10.
2. Tip at a restaurant: Your bill is $62 and you want to leave an 18% tip. Tip = (18 / 100) × 62 = $11.16.
3. Test score: You got 38 out of 50 questions right. Percent = (38 / 50) × 100 = 76%.
4. Discount: A $120 item is 35% off. Discount = (35 / 100) × 120 = $42. Sale price = $78.
5. Population growth: A city grew from 200,000 to 230,000 people. Percent increase = (30,000 / 200,000) × 100 = 15%.
6. Finding the whole: You know that 45 is 9% of some number. Whole = 45 / (9 / 100) = 45 / 0.09 = 500.

Working through examples like these is genuinely the fastest way to get comfortable with percentage math. The formulas start to feel automatic after a while.

A few percentage situations trip people up consistently. Here are the ones that come up most often, with clear explanations.

• "What is X% more than Y?" Multiply Y by (1 + X/100). For example, 20% more than 50 = 50 × 1.20 = 60.
• "What is X% less than Y?" Multiply Y by (1 − X/100). 15% less than 80 = 80 × 0.85 = 68.
• "A price increased by X%. What's the new price?" Same as above: Original × (1 + X/100).
• "After a Y% discount, the price is $Z. What was the original price?" Divide Z by (1 − Y/100). If $68 is the price after a 15% discount: 68 / 0.85 = $80.
• Stacking percentages: Two sequential discounts of 20% and 10% are not the same as a single 30% discount. On a $100 item: after 20% off you have $80, then 10% off that is $8 more, leaving $72 — not the $70 a flat 30% would give you.

That last one catches a lot of people off guard. Percentages compound, so sequential changes always need to be applied one at a time.

Percentages aren't just math-class problems. They're embedded in the financial and everyday decisions people make all the time.

Finance: Interest rates on loans, mortgages, and credit cards are expressed as percentages (usually APR). If you carry a $3,000 balance on a card with a 24% APR, you're paying roughly $720 per year in interest. Investment returns, savings account yields, and inflation rates all work the same way. Understanding percent change helps you evaluate whether an investment actually grew in real terms or just kept pace with inflation.

Shopping: Retail discounts are the most visible use of percentages. "40% off" sounds significant, but on a $25 item that's only $10 savings. Stacking a coupon on top of a sale price? Apply each discount sequentially, not together. Also watch for "percent off" versus "percent extra" offers. Getting 25% more product is not the same value as 25% off the price.

Grades and academic scores: Most grading systems are percentage-based. Teachers often use weighted percentages, where different categories (homework, tests, participation) count for different portions of your final grade. If your tests are worth 60% of your grade and you're averaging 72% on them, that component alone contributes 43.2 points to your final grade — so improving test scores moves the needle more than acing homework.

Once you see how percentages work in these areas, it's genuinely hard to unlearn it. You start doing quick mental math at the register, eyeballing whether a sale is actually good, or checking if a raise really beats inflation.

Here's a handy reference for common percent, decimal, and fraction equivalents. These are worth knowing by heart for quick mental math.

Bookmark this chart or keep it handy when you're working through problems. Recognizing these conversions on sight speeds up everything from mental estimates to formal calculations.