How do I find what percent one number is of another?

Divide the part by the whole and multiply by 100. Example: 30 of 150 is 30 ÷ 150 × 100 = 20%.

Can the percent change be negative?

Yes. A negative result means the new value is smaller than the old one — that's a decrease.

100% of a number is the number itself. 200% is double, and 50% is half.

Can I use decimals like 12.5%?

Yes. Decimal percentages work the same way — just divide by 100 (12.5 ÷ 100 = 0.125).

Why does percent change need an absolute value?

Using the absolute value of the old number keeps the sign of the result tied to the direction of change rather than the sign of the starting point.

How do I add a percent (like sales tax) to a price?

Multiply the price by (1 + rate/100). A $40 item with 8% tax is 40 × 1.08 = $43.20.

How do I work out the original price before a percent was added?

Divide the new total by (1 + rate/100). A $43.20 receipt that already includes 8% tax is 43.20 ÷ 1.08 = $40 pre-tax.

What's the difference between percent and percentage points?

If a conversion rate moves from 2% to 3%, that's a 1 percentage-point increase but a 50% relative increase. Headlines often mix these up.

Do two 50% discounts equal a free item?

No. Two stacked 50% discounts give 0.5 × 0.5 = 25% of the original price, which is a 75% total discount — still not free.

How do I use this for tip calculations?

Set mode to 'X% of Y', enter the tip percent and the bill, and the result is the tip in dollars. For splitting between people, use the dedicated Tip Calculator.

Is there a quick way to estimate percentages in my head?

Use 10% as your anchor — divide by 10 — then scale up or down. For example, 15% of 80 is 10% (= 8) plus half of that (= 4), so 12.

Percentage Calculator

Find a percent of a number, work out what percent one value is of another, or measure how much something has gone up or down — in a single tool. Useful for shoppers comparing deals, students checking test scores, freelancers calculating tax or commission, and small-business owners tracking month-over-month growth.

Last Updated: June 2026

Who this calculator helps

Shoppers checking how much they'll save on a sale or coupon.
Students working out a test score as a percentage of total marks.
Freelancers and self-employed workers estimating tax set-aside or commission.
Small-business owners measuring month-over-month growth or shrinkage in sales.
Anyone reading a news headline that quotes a percent change and wants to sanity-check the math.

What do you want to calculate?

Value X

Value Y

20% of 150

All calculations are estimates based on average platform fees. Real profits may vary depending on category, ads, and shipping.

How to use this calculator

Enter your numbers in each field above — the calculator updates instantly as you type, so there's nothing to submit.
Use your real figures when you have them, or sensible estimates while you're planning. If a field doesn't apply, leave it at zero.
Compare the results, then change one input at a time to see how each lever (price, cost, fees, volume) moves the outcome.

When to use this calculator

Comparing two prices to see which discount is actually bigger.
Calculating a tip when you're away from the Tip Calculator on this site.
Working out how much your salary or rent went up or down year over year.
Translating fractions and decimals into percentages (or the reverse) for school or work.
Measuring marketing performance: open rates, click-through rates, and conversion rates.

Formula

X% of Y = (X ÷ 100) × Y · % change = ((New − Old) ÷ |Old|) × 100

Worked example

What is 20% of 150?

Turn 20% into a decimal: 20 ÷ 100 = 0.20
Multiply by the whole: 0.20 × 150 = 30

Answer: 30

More worked examples

What percent of 240 is 36?

Divide the part by the whole: 36 ÷ 240 = 0.15
Multiply by 100 to turn the decimal into a percent: 0.15 × 100 = 15%

Answer: 15%

A subscription went from $12 per month to $15 per month — what's the percent change?

Difference: 15 − 12 = 3
Divide by the old value: 3 ÷ 12 = 0.25
Multiply by 100: 0.25 × 100 = 25%

Answer: 25% increase

Your portfolio fell from $8,400 to $7,560 — what percent did it drop?

Difference: 7,560 − 8,400 = −840
Divide by the old value: −840 ÷ 8,400 = −0.10
Multiply by 100: −10%

Answer: 10% decrease

How it works

Percent literally means "per hundred", so any percentage is just a fraction with 100 on the bottom. Converting it to a decimal first keeps the arithmetic simple on paper or in your head — for example, 18% becomes 0.18.

For a "percent of" calculation, multiply the decimal by the whole. For a "what percent is X of Y" calculation, divide the part by the whole and then multiply by 100. Both questions are really the same equation rearranged.

Percent change measures the gap between an old and a new value relative to the old value. Subtract old from new, divide by the old value, then multiply by 100. A positive number is an increase, a negative number is a decrease, and the size of the percentage tells you how big the move was.

If you only need a quick markup or markdown, multiply the original by (1 + percent/100) for an increase or (1 − percent/100) for a decrease. That single multiplication answers both "what's the new total?" and "what's the running balance after this change?" in one step.

Expert tips

When you stack percentages — for example a 10% raise followed by a 5% raise — multiply the factors (1.10 × 1.05 = 1.155, a 15.5% total increase). Adding the two percentages together gives the wrong answer.
A drop from 100 to 50 is a 50% decrease, but going back from 50 to 100 is a 100% increase. Percentages are not symmetric.
To reverse a percent change, divide by the multiplier instead of subtracting the percent. A price after a 20% markup is the original × 1.20, so divide by 1.20 to get back to the original.
Percentage points and percent are different. A conversion rate moving from 2% to 3% is a 1 percentage-point rise, but a 50% relative increase.
When the starting value is zero, percent change is undefined — there's nothing to compare against. State the absolute change instead.

How to interpret your results

Dollar values are shown per sale, per order, or per item unless a result is explicitly labelled monthly, weekly, or daily.
Percentages (margin, ROI, conversion rate) are easier to compare across products and price points than raw dollars — use them when you benchmark.
A positive result means you're ahead after the costs and fees you entered. A negative result means the current numbers don't work — change a lever (raise price, cut a cost, lower ad spend) and recalculate.
Treat the output as a planning estimate, not a guarantee. Fees, taxes, and conversion rates shift over time — re-run the numbers whenever a key input changes.

Limitations

The tool does not apply tax, fees, or rounding rules for any specific country or store. It returns the pure mathematical result.
It does not compound multiple percentages automatically — run them one at a time if you're stacking discounts, taxes, or raises.
Very large or very small numbers may display with rounding for readability; the underlying calculation uses full precision.

Common mistakes

Adding two percentages from different totals — they only add up if both are calculated from the same base.
Dividing by the new value instead of the old value when measuring percent change.
Forgetting to convert the percent to a decimal before multiplying (using 20 instead of 0.20).
Confusing percentage points with percent change when comparing rates such as interest, conversion, or unemployment.

Go deeper with plain-English guides on the same topic.

FAQ

How do I find what percent one number is of another?: Divide the part by the whole and multiply by 100. Example: 30 of 150 is 30 ÷ 150 × 100 = 20%.
Can the percent change be negative?: Yes. A negative result means the new value is smaller than the old one — that's a decrease.
What does 100% mean?: 100% of a number is the number itself. 200% is double, and 50% is half.
Can I use decimals like 12.5%?: Yes. Decimal percentages work the same way — just divide by 100 (12.5 ÷ 100 = 0.125).
Why does percent change need an absolute value?: Using the absolute value of the old number keeps the sign of the result tied to the direction of change rather than the sign of the starting point.
How do I add a percent (like sales tax) to a price?: Multiply the price by (1 + rate/100). A $40 item with 8% tax is 40 × 1.08 = $43.20.
How do I work out the original price before a percent was added?: Divide the new total by (1 + rate/100). A $43.20 receipt that already includes 8% tax is 43.20 ÷ 1.08 = $40 pre-tax.
What's the difference between percent and percentage points?: If a conversion rate moves from 2% to 3%, that's a 1 percentage-point increase but a 50% relative increase. Headlines often mix these up.
Do two 50% discounts equal a free item?: No. Two stacked 50% discounts give 0.5 × 0.5 = 25% of the original price, which is a 75% total discount — still not free.
How do I use this for tip calculations?: Set mode to 'X% of Y', enter the tip percent and the bill, and the result is the tip in dollars. For splitting between people, use the dedicated Tip Calculator.
Is there a quick way to estimate percentages in my head?: Use 10% as your anchor — divide by 10 — then scale up or down. For example, 15% of 80 is 10% (= 8) plus half of that (= 4), so 12.

Why trust this calculator?

This tool uses standard mathematical formulas and commonly accepted calculation methods, shown openly in the Formula section above so you can verify the math yourself. Results are estimates based on the information you enter and do not account for every individual circumstance. For important financial, tax, legal, medical, or business decisions, please double-check with a qualified professional before acting on the numbers.

Keep going

One calculator rarely tells the full story. Pair this one with a related tool below to pressure-test your numbers from a different angle, or browse Everyday Math Calculators for more in the same category.

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