Percentage Calculator
Calculate percentages, percentage change, and what percent one number is of another. Free online percentage calculator for everyday math.
How to Use Percentage Calculator
- 1Choose a calculation mode from the three tabs: "X% of Y", "X is what % of Y", or "% Change".
- 2Enter the required numbers in the input fields shown.
- 3Click Calculate to get the result instantly.
- 4The formula used is shown below the result for verification.
- 5Switch between tabs to perform different percentage calculations without reloading.
About Percentage Calculator
The Percentage Calculator handles the three most common percentage problems: finding what X% of a number is, figuring out what percentage one number is of another, and calculating percentage increase or decrease between two values. It is ideal for students, shoppers calculating discounts, analysts measuring growth, and anyone needing quick percentage math.
How Percentage Calculator Works
Percentage calculations express one number as a fraction of 100 and are among the most frequently needed pieces of arithmetic in everyday life. Our calculator handles the three fundamental percentage problems. Mode 1 ("X% of Y") computes what a given percentage of a number is — used for calculating discounts, tips, tax amounts, and commission. Mode 2 ("X is what % of Y") answers the question "what fraction of the total is this part?" — used for analysing test scores, market share, and budget breakdowns. Mode 3 ("% Change") measures how a value has changed relative to its original — used in finance, science, and journalism to describe growth, decline, inflation, and returns. All three formulas are displayed alongside the result so you can verify the calculation or copy the formula for use in a spreadsheet. Results are rounded to four decimal places to eliminate floating-point noise while retaining precision for financial and statistical applications.
Mode 1: Result = (X ÷ 100) × Y
Mode 2: Result = (X ÷ Y) × 100
Mode 3: % Change = ((New − Old) ÷ |Old|) × 100Example: three typical calculations
- Mode 1 — 15% tip on a $67 restaurant bill: (15 ÷ 100) × 67 = $10.05
- Mode 2 — A student scored 43 out of 55: (43 ÷ 55) × 100 = 78.18%
- Mode 3 — Stock price went from $120 to $145: ((145 − 120) ÷ 120) × 100 = +20.83%
Tip: $10.05 · Score: 78.18% · Price change: +20.83%
Reference Data
Quick Percentage Reference Table (% of 100, 500, 1000, 5000)
| Percentage | of 100 | of 500 | of 1,000 | of 5,000 |
|---|---|---|---|---|
| 1% | 1 | 5 | 10 | 50 |
| 5% | 5 | 25 | 50 | 250 |
| 10% | 10 | 50 | 100 | 500 |
| 15% | 15 | 75 | 150 | 750 |
| 20% | 20 | 100 | 200 | 1,000 |
| 25% | 25 | 125 | 250 | 1,250 |
| 33.33% | 33.33 | 166.67 | 333.33 | 1,666.67 |
| 50% | 50 | 250 | 500 | 2,500 |
| 75% | 75 | 375 | 750 | 3,750 |
| 100% | 100 | 500 | 1,000 | 5,000 |
Who Uses This Tool and Why
- ✓Shoppers calculate the actual saving from a "30% off" sale before deciding whether a purchase is worth it.
- ✓Students and teachers convert raw scores into percentage grades and quickly check whether a mark meets a passing threshold.
- ✓Financial analysts calculate month-over-month and year-over-year percentage change in revenue, expenses, and key performance indicators.
- ✓Business owners calculate VAT/sales tax amounts, profit margins as a percentage of revenue, and commission rates for sales teams.
- ✓Scientists and engineers express measurement error, concentration changes, and efficiency gains as percentage differences for reports and papers.
Limitations & Practical Tips
Known Limitations
- •Percentage change is undefined when the original value is zero (division by zero) — the calculator will flag this edge case rather than returning an error or infinity.
- •Percentage calculations on very small numbers (e.g., finding 0.001% of 0.000003) may accumulate floating-point rounding errors — use the four-decimal result as a guide and verify with a dedicated scientific calculator for high-precision work.
- •The formula for "% of" assumes the percentage is a straightforward fraction of the whole. Compounding percentages (e.g. a 10% increase followed by another 10% increase) are not the same as a 20% increase — use the % Change formula twice in sequence for compound calculations.
Tips for Best Results
- →To quickly find 10% of any number, simply divide by 10 (move the decimal one place left). To find 5%, halve the 10% result. This is faster than a calculator for mental maths.
- →When comparing percentage change across items with different base values, a large percentage change on a small base can be misleading — always show the absolute change alongside the percentage.
- →To reverse a percentage (find the original price before a 20% discount was applied), divide the sale price by (1 − 0.20) = 0.80, not add 20% back, which would give the wrong answer.
Frequently Asked Questions
- How do I calculate what percentage one number is of another?
Switch to the "X is what % of Y" tab, enter the part (X) and the total (Y), and click Calculate. For example, 30 is 15% of 200.
- How do I calculate percentage increase or decrease?
Open the "% Change" tab, enter the original value and the new value, then click Calculate. A positive result indicates an increase; a negative result indicates a decrease.
- How accurate are the calculations?
Results are rounded to 4 decimal places to avoid floating-point noise while still being precise enough for financial and statistical use. The formula used is always shown below the result.
- What is the formula for calculating a percentage of a number?
Percentage of a number: Result = (Percentage ÷ 100) × Number. For example, 15% of 80 = (15 ÷ 100) × 80 = 0.15 × 80 = 12. You can also find it mentally by calculating 10% (divide by 10) and then halving it for 5%.
- How do I calculate a percentage discount?
Use Mode 1 ("X% of Y"): enter the discount percentage and the original price to get the discount amount. Then subtract from the original price to get the sale price. For example: 25% of $80 = $20 discount; sale price = $80 − $20 = $60.
- What is percentage change vs. percentage point change?
These are different. A percentage change measures the relative change from the original value — if a tax rate goes from 20% to 25%, that is a 25% change (5÷20×100). A percentage point change is the absolute arithmetic difference — in this case it is 5 percentage points. The distinction matters greatly in financial and political contexts.
- How do I find the original price before a percentage discount?
Divide the sale price by (1 − discount/100). If a product costs $60 after a 25% discount, the original price was $60 ÷ 0.75 = $80. Do not make the mistake of adding 25% to $60 — that gives $75, not the correct $80.
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Last updated: May 2, 2026 — Percentage Calculator by CalcDash.