Free Percentage Calculator Online 🔢
Calculate percentages, discounts, tips, percentage change, and more — 6 calculator types, instant results, no login needed.
Find the original value before a percentage was added or removed.
Free Percentage Calculator Online — Discounts, Tips, Percentage Change & More
Our free percentage calculator online covers every common percentage calculation in one place — finding a percentage of a number, calculating what percentage one number is of another, percentage increase and decrease, discount calculator, tip calculator with bill splitting, percentage error for science and business, and a reverse percentage calculator to find the original value before a percentage was applied. All results update instantly as you type — no calculate button needed.
How to Calculate a Percentage — The Basic Formula
The fundamental percentage formula is: Percentage = (Part ÷ Whole) × 100. To find a percentage of a number: Part = (Percentage ÷ 100) × Whole. For example, 15% of 240 = (15 ÷ 100) × 240 = 36. To find what percentage one number is of another: (36 ÷ 240) × 100 = 15%. These two formulas cover the majority of everyday percentage calculations — from calculating exam scores and shopping discounts to tax rates and financial ratios.
Percentage Increase and Decrease Calculator
Percentage change = ((New Value − Old Value) ÷ Old Value) × 100. A positive result is a percentage increase; negative is a percentage decrease. Examples: A salary rising from $50,000 to $57,500 = ((57,500 − 50,000) ÷ 50,000) × 100 = 15% increase. A stock price falling from $120 to $90 = ((90 − 120) ÷ 120) × 100 = −25% decrease. This calculator is used by investors tracking stock returns, HR professionals calculating salary changes, e-commerce teams analyzing conversion rate improvements, and students comparing test scores.
Discount Calculator — Shopping, Sales & Coupons
The discount calculator finds the final price and savings amount for any original price and discount percentage. Formula: Final Price = Original Price × (1 − Discount% ÷ 100). Savings = Original − Final. For example, a $350 jacket with a 30% discount costs $350 × 0.70 = $245, saving $105. This is useful for comparing prices across stores during sales, calculating the real value of coupon codes, and computing wholesale pricing with trade discounts for business purchases.
Tip Calculator with Bill Splitting
The tip calculator computes the tip amount, total bill, and per-person share for any bill and tip percentage. Standard tip percentages in the US: 15% for adequate service, 18% for good service, 20-25% for excellent service. For a $120 dinner bill with 20% tip: Tip = $24, Total = $144, Per person (4 people) = $36. This section is also useful for calculating service charges at hotels, gratuity at catered events, and per-person totals for group meals before splitting via Venmo or Zelle.
Percentage Error Calculator — Science & Business
Percentage error = |((Estimated − Actual) ÷ Actual)| × 100. It measures accuracy — how far an observed, estimated, or predicted value differs from the true accepted value. Used in: chemistry and physics labs to measure experimental accuracy, financial forecasting to measure prediction accuracy, quality control to measure defect rates, and engineering tolerances. A percentage error under 5% is generally considered acceptable in most science experiments. A percentage error above 10% typically indicates a measurement error or systematic bias that needs investigation.
Reverse Percentage Calculator — Find the Original Value
The reverse percentage calculator works backwards from a final value to find what the original value was before a percentage increase or decrease was applied. If a price after a 20% discount is $160, the original price = $160 ÷ (1 − 0.20) = $160 ÷ 0.80 = $200. If a value after a 15% tax increase is $345, the pre-tax value = $345 ÷ 1.15 = $300. This is useful for calculating pre-tax prices from tax-inclusive amounts, finding the pre-discount price from a sale price, and recovering the original figure from a marked-up wholesale price.
Frequently Asked Questions
How do I calculate a percentage of a number?
Divide the percentage by 100 and multiply by the number. Example: 20% of 150 = (20 ÷ 100) × 150 = 30. Use calculator ① above for instant results.
How do I calculate percentage increase or decrease?
Formula: ((New − Old) ÷ Old) × 100. Positive = increase, negative = decrease. Example: 80 to 100 = 25% increase. 100 to 80 = 20% decrease.
How do I calculate a discount percentage?
Final price = Original × (1 − discount% ÷ 100). Example: $200 with 25% off = $200 × 0.75 = $150. Savings = $50. Use calculator ④ above.
How do I calculate a tip percentage?
Tip = Bill × (tip% ÷ 100). For a $85 bill with 18% tip: $85 × 0.18 = $15.30 tip, $100.30 total. Use calculator ⑤ to split between multiple people.
What is percentage error?
|((Estimated − Actual) ÷ Actual)| × 100. Measures how far off an estimate is from the true value. Under 5% is generally acceptable in science experiments.
What is a reverse percentage calculator?
Finds the original value before a percentage was applied. Example: price after 20% discount is $160 → original = $160 ÷ 0.80 = $200. Use calculator ⑦ above.
About This Tool
This Percentage Calculator was built by the FreeImageTools team — students, finance professionals, and shoppers who calculate percentages daily for discounts, grades, financial analysis, and science work. The original tool had 2 calculators. We expanded it to 7 fully functional calculator types: basic percentage of a number, what percentage is X of Y, percentage change (increase/decrease), discount with savings, tip with bill splitting, percentage error, and reverse percentage. All results update in real time as you type — no button clicks needed. All calculations run in your browser. Reviewed in June 2026.