Percentage Calculator
MathCalculate what percent of a number is, find percentage of a total, or reverse-calculate the base value. Instant results for students and professionals.
Reviewed by the thecalcu.com team · Last updated July 6, 2026
A% of B
What is a Percentage?
A Percentage Calculator instantly computes four related percentage operations between any two numbers, covering every common percentage question in a single view. Rather than choosing which formula to apply, you enter Value A and Value B once, and the calculator simultaneously shows you A% of B, what percentage A is of B, what percentage B is of A, and the base number when A equals B% of it.
Percentages express a ratio on a common scale of 100, making them the universal language of comparisons: exam scores, GST rates, FD interest, discount offers, income tax slabs, profit margins, and market share statistics all use this format. The word comes from the Latin per centum, "per hundred", and the concept is anchored in Class 5 CBSE/ICSE textbooks before appearing in virtually every domain of adult life.
The challenge with percentages is that the same two numbers give different meaningful answers depending on which direction you ask the question. "25% of 200" (the answer is 50) is a different calculation from "25 is what percent of 200" (12.5%) and "200 is what percent of 25" (800%). All three results are useful in different contexts, and all three are visible the moment you enter your numbers.
The fourth output, "B% of what = A?", solves the reverse percentage problem: given a result and a percentage, find the original base. This is the formula behind reverse-calculating MRP from a discounted price, or finding the gross salary from TDS and tax rate. It is algebraically simple (A × 100 ÷ B) but easy to confuse with the other three operations.
Understanding percentage relationships between numbers is foundational for the Percentage Change Calculator, which uses these same operations to express how much one value has shifted relative to another over time.
Why Use a Percentage Calculator?
Percentage arithmetic is deceptively easy to get wrong, especially when the question changes form. Most people can compute "10% of 500" but struggle when the question is flipped ("500 is what percent of 800?") or reversed ("50 is 10% of what?"). This calculator eliminates that friction by computing all four answers simultaneously.
Four questions answered at once. Instead of recalling which formula applies to which question, you enter two numbers and read four results in a grid. This is particularly useful for students checking CBSE/ICSE homework, where percentage problems switch between all three formula types within the same exercise set.
Instant validation for financial calculations. When a bank says your FD earned 8% per annum interest of ₹6,400, you can verify the principal by the reverse formula: 6,400 × 100 ÷ 8 = ₹80,000. When a salary slip shows 12% EPF deduction of ₹2,400, you can confirm the gross salary: 2,400 × 100 ÷ 12 = ₹20,000.
Exam score benchmarking. Students use the "A is what % of B" output to convert raw marks to percentages and compare against cutoffs. A candidate with 312 marks can immediately see that 312 is 78% of 400, and confirm whether that clears a 75% cutoff.
No mode-switching. Unlike calculators with formula-type dropdowns, this tool shows all perspectives simultaneously, which is faster for users who need to reason about a number relationship rather than run a specific formula.
Who Should Use This Calculator?
Students in Class 5–12 and competitive exam aspirants. CBSE and ICSE curricula introduce all three percentage formula types by Class 7. This calculator is a direct study aid: enter the values from a textbook problem and verify your working. For JEE, NEET, CAT, and banking exam preparation, percentage proficiency is tested heavily, fast calculation of A% of B and reverse percentages is a timed skill.
Salaried professionals reviewing payslips. Monthly payslips are full of percentage relationships: DA as a % of basic, HRA deduction limits, EPF contribution rates, income tax TDS as % of gross. This calculator helps decode each line, enter the deduction amount and the percentage to verify the base salary, or enter the base and rate to verify the deduction.
Small business owners and traders. Calculating GST-inclusive and GST-exclusive prices, trade margins, and commission structures all reduce to percentage operations. The Discount Calculator handles retailer-specific use cases, but for general percentage relationships in pricing and procurement, this tool covers the full range.
Finance and accounting professionals. Ratio analysis, working capital percentages, budget utilisation, and variance analysis are all percentage computations. Having a four-output calculator removes the need to re-run formulas for each perspective of the same data.
What Insights Does the Percentage Calculator Give You?
A% of B is the most direct output, take a percentage of a base value. With A=25 and B=200, this tells you that 25% of 200 is 50. This number represents the actual quantity corresponding to the stated percentage: 18% GST on ₹10,000 is ₹1,800, or 10% commission on ₹3,50,000 property revenue is ₹35,000.
A is what % of B converts a raw number into a percentage of a reference value. 78 marks out of 120 is 65%; 42 defective units out of 1,400 produced is 3%. This output is used wherever performance needs to be expressed relative to a benchmark.
B is what % of A flips the reference point. If sales grew from ₹40 lakh (A) to ₹55 lakh (B), B is 137.5% of A, meaning the new figure is 37.5% higher than the old, or the new is 1.375 times the old. This perspective is particularly useful in year-on-year comparisons where you want to express the new value as a proportion of the previous one.
B% of what = A answers the reverse lookup: what must the base be for A to equal B% of it? If ₹40,000 is the TDS deducted at 20% (no-PAN rate), the gross payment was ₹40,000 × 100 ÷ 20 = ₹2,00,000. A 0 result for this output indicates B is 0, division by zero is protected.
How to use this Percentage calculator
Enter Value A, the number that plays the role of percentage, numerator, or result depending on which question you are asking. For "X% of a number", A is the percentage rate (e.g., 25). For "A is what % of B", A is the actual count or amount.
Enter Value B, the base or reference number. For "X% of a number", B is the base (e.g., 200). For "A is what % of B", B is the total or benchmark.
Read all four outputs at once, the results update live as you type. The highlighted primary result is A% of B (the most common query). The three secondary results give you the same pair of numbers viewed from every other angle.
Use the step breakdown, click "How was this calculated?" to see the working for each of the four formulas. This is useful for homework verification and for explaining the calculation to a client or colleague.
Interpret the fourth output carefully, "B% of what = A?" is the reverse formula. If B is 0, the output is 0 (undefined mathematically). For meaningful results, both A and B should be non-zero positive numbers.
Formula & Methodology
The calculator applies four percentage formulas simultaneously: Formula 1, A% of B: Result = (A ÷ 100) × B Formula 2, A is what % of B: Result = (A ÷ B) × 100 Formula 3, B is what % of A: Result = (B ÷ A) × 100 Formula 4, B% of what = A (reverse percentage): Result = (A × 100) ÷ B Variables: - A = Value A (the percentage rate in Formula 1; the part/numerator in Formulas 2 and 3; the known result in Formula 4) - B = Value B (the base in Formula 1; the whole/denominator in Formula 2; part in Formula 3; the percentage rate in Formula 4) Worked example, A = 15, B = 60: Formula 1: (15 ÷ 100) × 60 = 9 → 15% of 60 is 9Formula 2: (15 ÷ 60) × 100 = 25% → 15 is 25% of 60Formula 3: (60 ÷ 15) × 100 = 400% → 60 is 400% of 15Formula 4: (15 × 100) ÷ 60 = 25 → 60% of 25 = 15 Precision: All outputs are rounded to 4 decimal places. For exact integer results (e.g., 25% of 200 = 50.0000), the trailing zeros are dropped by the display layer. Edge cases: - If B = 0, Formulas 2 and 4 return 0 (division by zero protected) - If A = 0, Formula 3 returns 0 (division by zero protected) - Negative inputs are accepted, percentage relationships between negative numbers are valid in contexts like temperature change or negative returns
Frequently Asked Questions