Calculate Percentage Change and Discounts Online — Free Percentage Calculator
Use a free percentage calculator to find percentage increase, decrease, discounts, original price, and what percent one number is of another.
Why percentage calculations are easy to get wrong
Percentages look simple, but the wording can change the formula. “What is 15% of 240?” is different from “240 is what percent of 15?” A discount question is different from a percentage increase question. A reverse percentage question, such as finding the original price before a discount, needs another formula again.
UtilDen's Percentage Calculator puts the most common percentage problems in one place, so you can calculate price changes, discounts, grade scores, business growth, and before-and-after comparisons without doing the math by hand.
The three percentage formulas you need most often
Most everyday percentage questions fit into one of these patterns:
- Find X% of Y: multiply Y by X, then divide by 100. Example: 20% of 150 = 150 × 20 ÷ 100 = 30.
- Find what percent X is of Y: divide X by Y, then multiply by 100. Example: 45 out of 60 = 45 ÷ 60 × 100 = 75%.
- Find percentage change: subtract the old value from the new value, divide by the old value, then multiply by 100. Example: from 80 to 100 = 25% increase.
When you are in a hurry, the easiest option is to open the Percentage Calculator, enter the two numbers, and let the tool show the result instantly.
How to calculate percentage increase
Percentage increase tells you how much a number grew compared with its starting value. The formula is:
(New value − Old value) ÷ Old value × 100
If monthly sales increased from $2,000 to $2,600, the increase is $600. Divide 600 by 2,000 and multiply by 100. The result is 30%. This is useful for revenue growth, website traffic growth, app downloads, test score improvement, and weight or measurement changes.
How to calculate percentage decrease
Percentage decrease uses the same structure, but the new number is lower than the old number. If a file size drops from 5 MB to 3 MB, the decrease is 2 MB. Divide 2 by 5 and multiply by 100. The file size decreased by 40%.
This is helpful for checking price drops, budget cuts, weight changes, bounce rate improvements, file compression savings, and before-and-after performance metrics.
How to calculate a discount
For shopping, invoices, and pricing pages, percentages usually appear as discounts. To find the discount amount, multiply the original price by the discount percentage:
Discount amount = Original price × Discount % ÷ 100
If a $120 product has a 25% discount, the discount amount is $30. The sale price is $120 − $30 = $90. If you also need to add tax, calculate the discounted price first, then apply tax to the final taxable amount.
How to reverse a percentage
Reverse percentage is useful when you know the final value but need the original value. For example, if a product costs $80 after a 20% discount, $80 is not the original price minus $20. It is 80% of the original price.
The formula is:
Original price = Final price ÷ (1 − discount rate)
So $80 after a 20% discount means $80 ÷ 0.8 = $100. This same idea works for reversing increases too. If a value after a 10% increase is $110, divide by 1.1 to get the original value of $100.
Percentage vs percentage points
This is one of the most common percentage mistakes. If a conversion rate goes from 4% to 6%, it increased by 2 percentage points. But relative to the original 4%, the increase is 50% because 2 is half of 4.
Use percentage points when comparing two rates directly. Use percentage change when describing how much the metric grew or dropped relative to the starting point.
Common ways to use a percentage calculator
A percentage calculator is useful beyond school math. You can use it to calculate discounts, tips, tax estimates, grade percentages, profit margins, revenue growth, traffic changes, conversion rates, salary increases, and before-and-after comparisons.
For date-based math, use the Age Calculator. For restaurant bills, use the Tip Calculator. For unit-based problems, explore Unit Converters. For more calculation tools, visit the full Math & Science category.
Try the free percentage calculator
Open UtilDen's free Percentage Calculator whenever you need to calculate percent of a number, percentage change, increase, decrease, discounts, or reverse percentages. It is fast, browser-based, and built for simple everyday math.
Free Math Tool
Calculate percentages, discounts, and changes instantly
Use the calculator for price drops, grade scores, growth rates, and before-and-after comparisons.
Open Percentage Calculator →Frequently Asked Questions
How do I calculate percentage change? +
Use (new value minus old value) divided by old value, then multiply by 100. A positive result is an increase and a negative result is a decrease.
How do I calculate a discount percentage? +
Discount percentage = discount amount divided by original price times 100. If a $100 item is reduced by $25, the discount is 25%.
How do I find the original price after a percentage discount? +
Divide the sale price by 1 minus the discount rate. For example, if $80 is the price after a 20% discount, the original price is 80 ÷ 0.8 = $100.
What is the difference between percent and percentage points? +
Percentage points measure the direct difference between two percentages. Percent measures relative change. Going from 10% to 12% is +2 percentage points, but a 20% relative increase.
Can I use this calculator for grades, prices, and business metrics? +
Yes. A percentage calculator works for test scores, sales discounts, tax estimates, conversion rates, growth rates, and before-and-after comparisons.