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Algebra

Percentage Change Calculator

Calculate percent change between two values. Free online Percentage Change Calculator. Calculate percentage change online — fast, accurate, mobile-friendly, no

Change
25%

Derivation

  1. ├── 01Givena = 100, b = 125
  2. ├── 02Formula{let t=e.a;return(e.b-t) / t × 100}
  3. ├── 03Substitute{let t=e.100;return(e.125-t) / t × 100}
  4. └── 04Compute Change25
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§01What is

Understanding the Percentage Change Calculator

The Percentage Change Calculator computes Change from 2 inputs: old value, new value. Calculate percent change between two values.

Algebra is the art of solving for the unknown. Rearranging a formula to isolate the variable you actually need is the single most common real-world math skill — and doing it with real numbers under time pressure is where errors happen. The Percentage Change Calculator sits in that toolkit — it calculate percent change between two values. Enter your numbers above and the result updates instantly; every step of the math is shown in the Derivation panel so you can see exactly how the answer was reached.

§02The Formula

How it’s calculated

{let t=e.a;return(e.b-t) / t × 100}

Where

a
Old value
b
New value
§03Practical Example

Step-by-step walkthrough

Scenario

Apply the formula to a realistic set of inputs: Old value = 100, New value = 125.

  1. 01Start by noting the input — Old value: 100.
  2. 02Start by noting the input — New value: 125.
  3. 03Substitute these values into the formula: {let t=e.a;return(e.b-t) / t × 100}
  4. 04Compute Change: the calculator returns 25.
  5. 05Cross-check the answer by opening the Derivation panel above — every line of math is shown so you can follow the computation end-to-end.
§04Variants

Common Percentage Change Problems

The formula gets rearranged depending on which variable you need. Here are the patterns you’ll run into in the real world — find the one that matches your problem and follow the worked steps.

01 · PATTERN

Old value halved

a = 50 (from 100)

Keep every other input at its default and halve the old value. See how change responds.

  1. 01New Old value: 50
  2. 02Baseline Change: 25
  3. 03New Change: 150
  4. 04Change increases by 500% → use this sensitivity to plan for real-world variation.
02 · PATTERN

Old value doubled

a = 200 (from 100)

Keep every other input at its default and double the old value. See how change responds.

  1. 01New Old value: 200
  2. 02Baseline Change: 25
  3. 03New Change: -37.5
  4. 04Change decreases by 250% → use this sensitivity to plan for real-world variation.
03 · PATTERN

New value halved

b = 62.5 (from 125)

Keep every other input at its default and halve the new value. See how change responds.

  1. 01New New value: 62.5
  2. 02Baseline Change: 25
  3. 03New Change: -37.5
  4. 04Change decreases by 250% → use this sensitivity to plan for real-world variation.
04 · PATTERN

New value doubled

b = 250 (from 125)

Keep every other input at its default and double the new value. See how change responds.

  1. 01New New value: 250
  2. 02Baseline Change: 25
  3. 03New Change: 150
  4. 04Change increases by 500% → use this sensitivity to plan for real-world variation.
§05FAQ

Frequently asked questions

Yes. The calculator implements the standard formula as documented and returns exact floating-point results. No approximations are used unless noted in the formula.
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