Percentage Calculator Free
Calculate any percentage instantly — find X% of a number, what percent one value is of another, percentage change between two numbers, or apply an increase/decrease. No signup, runs entirely in your browser.
⏱ 5 min read · Complete guide below
How the Percentage Calculator Works
- 1Select a calculation mode — X% of Y, what percent, percentage change, or increase/decrease.
- 2Enter your two values in the input fields. Labels update to show you exactly what each field means for the selected mode.
- 3The result appears instantly as you type — no button to press.
- 4The formula is shown below the result so you can see exactly how the calculation was done.
Percentage Formulas
Every mode uses a standard mathematical formula. X% of Y: result = (X ÷ 100) × Y. X is what % of Y: result = (X ÷ Y) × 100. Percentage change: result = ((New − Old) ÷ |Old|) × 100. Increase by X%: result = Y × (1 + X/100). Decrease by X%: result = Y × (1 − X/100).
Worked Example: Comparing Two Credit Card Rewards Rates
Card A pays a flat 2% cashback on everything. Card B pays 5% on the first $1,000 of monthly spend and 1% on the rest. On $2,400 of monthly spend: Card A earns 2% × $2,400 = $48. Card B earns 5% × $1,000 = $50 on the first tier, plus 1% × $1,400 = $14 on the remainder, for a total of $64 — a tiered rate with a lower headline number on part of your spend can still out-earn a higher flat rate once you do the blended math.
This is exactly the kind of comparison the X% of Y mode handles: run each tier separately (5% of $1,000, then 1% of $1,400) and add the results, rather than applying a single percentage to the full amount, which would understate Card B by treating its bonus category rate as if it applied to your whole budget.
The Percentage Mistakes That Trip People Up
Percentages are simple arithmetic but they hide a few traps worth knowing. The first is confusing percentage points with percent: if an interest rate rises from 4% to 6%, that is a 2 percentage-point increase, but a 50 percent increase in the rate itself — headlines and arguments often blur the two. The second is the asymmetry of increase and decrease: raising a number by a percentage and then cutting it by the same percentage does not return you to the start, because each percentage applies to a different base. A stock that falls 50% then rises 50% is still down 25%, and famously a 50% loss needs a 100% gain just to break even — a fact this calculator's “percentage change” mode makes easy to verify. The third is mixing up “X% of” with “X% off”: 20% of $50 is the $10 discount, while 20% off $50 is the $40 you actually pay. Keeping these distinctions straight — and using the mode that matches exactly what you are asking — prevents the small slips that turn into real money errors on taxes, discounts, and investment returns.
Common Percentage Calculations
Sales Tax
Use "Increase by X%" to add tax to a price. Enter the tax rate as X and the pre-tax price as Y to get the total including tax.
Discount Price
Use "Decrease by X%" to apply a discount. Enter the discount percentage and the original price to get the sale price instantly.
Exam Scores
Use "X is what % of Y" to convert marks to a percentage. Enter your score as X and the total marks as Y.
Profit / Loss
Use "Percentage change" to calculate profit or loss percentage. Enter the cost price as the original value and the selling price as the new value.
Tip Calculation
Use "X% of Y" to calculate a tip. Enter the tip percentage (e.g. 15 or 20) and the bill total to get the tip amount.
Population / Growth
Use "Percentage change" to measure year-over-year growth. Enter last year's value as original and this year's as new.
Frequently Asked Questions
How do I calculate what percentage one number is of another?
Divide the part by the whole, then multiply by 100. For example, to find what percentage 30 is of 200: (30 ÷ 200) × 100 = 15%. Use the "X is what % of Y" mode in the calculator — enter 30 as X and 200 as Y.
How do I calculate a percentage of a number?
Multiply the number by the percentage divided by 100. For example, 15% of 200 = (15 ÷ 100) × 200 = 30. Use the "X% of Y" mode — enter 15 as the percentage and 200 as the number.
How is percentage change calculated?
Percentage change = ((New Value − Original Value) ÷ |Original Value|) × 100. A positive result means an increase; negative means a decrease. For example, from 80 to 100: ((100 − 80) ÷ 80) × 100 = +25%.
What is the difference between percentage increase and percentage change?
Percentage change measures how much a value changed relative to its original — it can be positive (increase) or negative (decrease). Percentage increase specifically refers to a positive change. The "Percentage change" mode covers both; the "Increase / Decrease" mode lets you apply a percentage to a starting number to get a new value.
How do I increase a number by a percentage?
Multiply the number by (1 + percentage/100). For example, to increase 500 by 20%: 500 × 1.20 = 600. Use the "Increase / Decrease" mode, set to Increase, enter 20% and 500.
Is this calculator free and does it store my inputs?
Yes, completely free — no signup, no account required. All calculations run entirely in your browser using JavaScript. No data is sent to any server.
How do I calculate sales tax on a price?
Use the "Increase by X%" mode. Enter the tax rate as X (e.g. 8 for 8%) and the pre-tax price as Y. The result is the total price including tax. For example, 8% tax on $45: 45 × 1.08 = $48.60.
How do I work out a percentage discount?
Use the "Decrease by X%" mode. Enter the discount percentage and the original price. For example, a 25% discount on $120: 120 × (1 − 0.25) = $90. The saving is $30, which you can verify with "X% of Y": 25% of 120 = 30.
Why do percentage increase and decrease not cancel each other out?
Because each percentage is applied to a different base. Increasing 100 by 50% gives 150. Decreasing 150 by 50% gives 75 — not 100. The asymmetry occurs because 50% of 150 is larger than 50% of 100. This matters in finance: a 50% portfolio loss requires a 100% gain to recover.