Percentages Are Everywhere. Most People Calculate Them Wrong.
A store says 30% off. You want to know the final price. Your salary increased by 8%. You want to know how much extra that is per month. Your test score was 43 out of 56. You want to know what percentage that is. A product costs $85 now and used to cost $110. You want to know how much the price dropped in percentage terms.
These are four different percentage calculations. Most people know vaguely how percentages work but regularly reach for a calculator for any of these because the formulas are not immediately obvious. This tool handles all of them — and several more — without requiring you to remember a single formula.
—The Six Most Common Percentage Calculations
What is X% of Y?
The most basic percentage calculation. What is 20% of $85? What is 15% of 240? What is 7.5% of $1,200?
Formula: Result = (X ÷ 100) × Y
Example: 20% of 85 = (20 ÷ 100) × 85 = 0.20 × 85 = 17
Use for: discounts, tips, tax calculations, commission calculations, interest on a fixed amount.
X is what percentage of Y?
You have two numbers and want to express the relationship as a percentage. You scored 43 out of 56. What percentage is that? Your team completed 34 of 50 tasks. What is the completion rate?
Formula: Percentage = (X ÷ Y) × 100
Example: 43 out of 56 = (43 ÷ 56) × 100 = 76.79%
Use for: test scores, completion rates, market share, survey results, batting averages.
Percentage Increase
A value went up. By what percentage? Your salary went from $45,000 to $48,600. Your portfolio went from $10,000 to $12,400. Your website traffic went from 3,200 to 4,800 monthly visitors.
Formula: Increase % = ((New − Old) ÷ Old) × 100
Example: From 45,000 to 48,600 = ((48,600 − 45,000) ÷ 45,000) × 100 = (3,600 ÷ 45,000) × 100 = 8%
Use for: salary increases, investment returns, business growth metrics, price changes.
Percentage Decrease
A value went down. By what percentage? A product went from $110 to $85. Your commute time dropped from 45 minutes to 32 minutes. Your monthly expenses went from $3,400 to $2,900.
Formula: Decrease % = ((Old − New) ÷ Old) × 100
Example: From 110 to 85 = ((110 − 85) ÷ 110) × 100 = (25 ÷ 110) × 100 = 22.73%
Use for: price reductions, cost savings, performance improvements, discount verification.
Add a Percentage to a Number
A bill is $240 and you need to add 8% tax. A salary is $52,000 and it increases by 5%. A price is $89 and you want to add a 20% markup.
Formula: Result = Original × (1 + Percentage ÷ 100)
Example: $240 + 8% tax = 240 × 1.08 = $259.20
Use for: adding tax, applying markups, calculating raises, projecting growth.
Subtract a Percentage from a Number
An item costs $150 and is 25% off. Your hourly rate is $85 and a client requests a 10% discount. A subscription is $299 and there is a 15% loyalty discount.
Formula: Result = Original × (1 − Percentage ÷ 100)
Example: $150 minus 25% = 150 × 0.75 = $112.50
Use for: discounts, reductions, negotiated price cuts, after-tax calculations.
—Common Percentage Mistakes and How to Avoid Them
Reversing a percentage change is not the same percentage. If a price increases by 20% and then decreases by 20%, you do not end up back at the original price. Starting at $100, a 20% increase gives $120. A 20% decrease from $120 gives $96, not $100. The percentages are applied to different base numbers. To reverse a 20% increase, you need to decrease by 16.67%.
Percent versus percentage points. If an interest rate rises from 3% to 5%, it increased by 2 percentage points — but it increased by 66.7 percent. These are completely different statements. Politicians and media often conflate these deliberately or accidentally. “Interest rates rose by 2%” and “interest rates rose by 2 percentage points” mean entirely different things.
The base matters for percentage calculations. A 50% discount followed by an additional 20% off is not 70% off. The 20% is calculated on the already-discounted price. A $100 item at 50% off is $50. An additional 20% off $50 is $10 off, giving $40. Total discount from original: 60%, not 70%.
—Quick Percentage Mental Math
For round numbers, percentage calculations can be done quickly in your head with these techniques:
10% — Move the decimal one place to the left. 10% of 340 = 34.
5% — Calculate 10% and halve it. 5% of 340 = 17.
1% — Move the decimal two places to the left. 1% of 340 = 3.4.
20% — Calculate 10% and double it. 20% of 340 = 68.
25% — Divide by 4. 25% of 340 = 85.
50% — Divide by 2. 50% of 340 = 170.
75% — Calculate 50% and add 25%. 75% of 340 = 170 + 85 = 255.
—Frequently Asked Questions
What is the difference between percent and percentage?
Percent (%) refers to a specific rate — “a 20 percent discount.” Percentage refers to the result of a percentage calculation — “what percentage of the total is this?” In everyday use they are often interchangeable, but in precise writing they have distinct roles.
How do I calculate percentage change?
Subtract the old value from the new value, divide by the old value, then multiply by 100. A positive result is an increase, a negative result is a decrease. This tool calculates percentage change instantly when you enter the two values.
What does basis point mean?
One basis point equals 0.01 percent. Basis points are used in finance and economics to describe small changes in rates or yields with precision. A 25 basis point increase in an interest rate is a 0.25 percent increase.
How do I find the original price before a discount?
If you know the discounted price and the discount percentage, divide the discounted price by (1 minus the discount as a decimal). A $75 price after a 25% discount means the original was $75 ÷ 0.75 = $100.
Is this tool free?
Yes, completely free with no account required.
—Enter Your Numbers. Get Your Percentage. Done.
Six types of percentage calculations. All of them handled instantly. No formulas to remember, no mental arithmetic required. Select the calculation type, enter your numbers, and get the answer.