How to use this percentage calculator
Each row is a different question—type numbers in the sentence-style boxes at the top of the page. Results update as you type. Percentages can be entered with or without a % sign.
Common percentage formulas
What is X% of Y? Result = (X ÷ 100) × Y. Example: 15% of 200 = 30.
Add or subtract a percent: New value = Y × (1 ± X/100). Example: 200 + 10% = 220.
Percent change from old to new: ((new − old) ÷ |old|) × 100. A rise from 80 to 100 is +25%.
What percent is A of B? (A ÷ B) × 100 when B ≠ 0.
Original price before a discount: sale price ÷ (1 − discount/100). Example: $40 after 20% off → $50.
Price before tax: tax-included price ÷ (1 + tax rate/100).
Example: sale price after 20% off
Original price $50, discount 20%. Use subtract percent: 50 with 20% off → $40. Or use “X% of Y” to see the discount amount ($10).
When you might use percentages
Retail discounts, sales tax lines on receipts, commission on sales, year-over-year growth headlines, and grade weights often arrive as percents. Scroll to the row you need—related tools include the tip calculator, fraction calculator, and ratio calculator on the math hub.
Example: salary raise
Salary $55,000 with a 4% raise: use add percent with base 55000 and 4 → $57,200. Percent change from 55000 to 57200 should read about 4% as a consistency check.
Example: what percent is the down payment?
Down payment $45,000 on a $300,000 home → what-percent mode with part 45000 and whole 300000 → 15%.
Common mistakes
- Applying a second discount to an already-reduced price without noticing the base changed.
- Mixing percentage points with percent change (a rate moving from 2% to 3% is 1 point, not a 50% change of the rate).
- Dividing by zero in “what percent” when the whole is 0.
What is 20 percent of 100?
20% of 100 is 20. Enter 20 and 100 in the first row (what is X% of Y).
How do you calculate a percentage of a number?
Use (percent ÷ 100) × number. On CalcTool, use the first row; see also the math calculators hub for fractions and ratios.
How do you calculate percent increase or decrease?
Percent change = ((new − old) ÷ |old|) × 100. Use the percent change row (e.g. 80 → 100 gives +25%).
How do you calculate 20 percent off a price?
Sale price = original × (1 − 20/100). Use the “decreased by a percent” row with base 50 and 20 → $40; discount amount is $10 via the first row.
How do you find the original price before a discount?
Original = sale ÷ (1 − discount/100). Use the “original price before a discount” row: 20% off and $40 sale → $50 original.
How do you find the price before tax?
Pre-tax = tax-included price ÷ (1 + tax/100). Use the “price before tax” row—example $113 with 13% tax → $100 before tax.
What percent is one number of another?
Answer = (part ÷ whole) × 100. Use the “X is what % of Y” row—down payment $45,000 on $300,000 → 15%.
Is tipping the same as calculating a percent?
Yes—gratuity is a percent of the bill. After percent practice here, use the tip calculator for totals and per-person splits on the everyday calculators hub.
When should I use fractions instead of percents?
Exact rational answers (1/3, 3/8) fit the fraction calculator. Percents fit discounts, tax rates, and quick comparisons.
How do I split an amount by ratio instead of percent?
Weights like 2:3:5 use the ratio calculator—different from “what percent is A of B?” on this page.