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Percentage Calculator

Online percentage calculator for daily math

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Common questions (FAQ)

10 quick answers with worked examples and links to the matching FAQ page. Open the Percentage Calculator above to try the same patterns with your numbers.

Guide

Formulas in LaTeX notation, numeric walkthroughs, and quick links into each calculator tab.

Formulas

Each mode uses a standard definition below. Symbols match the fields in the calculator tabs.

Basic Percentage

Formula

P=r100⋅NP = \frac{r}{100} \cdot N

P = result amount, r = percentage (%), N = base number.

Step-by-step

Example: What is 20% of 100?

StepCalculation
Substituter = 20, N = 100
Apply formulaP = (20 ÷ 100) × 100 = 0.2 × 100
ResultP = 20
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Percentage Change

Formula

C=Nnew−NoldNold×100C = \frac{N_{\text{new}} - N_{\text{old}}}{N_{\text{old}}} \times 100

C = percent change (%), Nold = original value, Nnew = new value (C > 0 increase, C < 0 decrease).

Step-by-step

Example: Value rises from 80 to 100.

StepCalculation
SubstituteN_old = 80, N_new = 100
Numerator100 − 80 = 20
Divide & × 100C = (20 ÷ 80) × 100 = 0.25 × 100
ResultC = 25%
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Percentage Of (part vs whole)

Formula

Q=BA×100Q = \frac{B}{A} \times 100

Q = what percent B is of A, A = total (whole), B = part (A ≠ 0).

Step-by-step

Example: What percent of 200 is 40?

StepCalculation
SubstituteA = 200, B = 40
RatioB ÷ A = 40 ÷ 200 = 0.2
ResultQ = 0.2 × 100 = 20%
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Value After Change

Formula

V=V0⋅(1+p100)V = V_0 \cdot \left(1 + \frac{p}{100}\right)

V = final value, V0 = starting value, p = change in % (negative for decrease).

Step-by-step

Example: 2,000 after a 15% decrease (discount).

StepCalculation
SubstituteV₀ = 2,000, p = −15
Factor1 + (−15 ÷ 100) = 1 − 0.15 = 0.85
MultiplyV = 2,000 × 0.85
ResultV = 1,700
Try it now

1. How can I use the percentage calculator tabs for discounts, tips, or grades?

  1. Basic Percentage: Enter a percentage and a number to find X% of that number.
  2. Percentage Change: Enter original and new values to calculate the percentage increase or decrease.
  3. Percentage Of: Enter total (A) and part (B) to see what percent B is of A.
  4. Value After Change: Enter a starting value and a percent change (negative for decrease) to get the final value.
  5. Results update as you type. Use Reset to clear the current tab. Recent calculations are saved locally (up to five).

2. How does this percentage calculator apply formulas in each mode?

Basic: Result = (Percentage ÷ 100) × Number.

Change: ((New Value − Old Value) ÷ Old Value) × 100.

Percentage Of: (Part ÷ Total) × 100.

Value After Change: Starting Value × (1 + Change% ÷ 100).

All calculations run in your browser. History is stored only in your browser (localStorage).

3. What percentage problems does this tool solve, and how is it organized?

Free online percentage calculator for everyday math. Calculate discounts, tax, growth rates, and more.

Use it for shopping, investments, grades, or any percentage-related calculation.

4. Why use a multi-tab percentage calculator in the browser?

  • Four modes: Basic, change, part-of-whole, and value after a percent change.
  • Real-time results, comma-formatted numbers, and a short sentence explaining each result.
  • Recent history with one-click restore. No signup required.
  • Works on any device with a browser.

5. When do people rely on percentage math for finance, school, or shopping?

  • Shopping: Calculate discount amounts and final prices.
  • Finance: Investment returns, interest, and tax.
  • Academics: Test scores and grade percentages.
  • Business: Sales growth and revenue change.
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