Percentage Change & Comparison Calculator
Quickly solve common percentage questions without manual arithmetic.
Use the Percentage Calculator
Solve three common percentage problems.
Calculations and text processing happen locally in your browser. ToolLott does not send these inputs to a server for this tool.
How to use it
Choose the percentage question, enter A and B, then calculate.
How the Percentage Calculator works
The Percentage Calculator solves three common percentage questions: finding A percent of B, finding what percentage A is of B, and calculating percentage change.
Calculation breakdown
ToolLott will explain the current inputs and displayed result here.
Percentage formulas used by ToolLott
The formula changes with the selected question. ToolLott keeps A and B visible so the user can see which value acts as the percentage, part, whole, original value or new value.
Result = (A / 100) x BUse when A is the percentage rate and B is the base value.
Percentage = (A / B) x 100B cannot be zero.
Change % = (B - A) / |A| x 100A is the original value and cannot be zero.
| Symbol / input | Meaning | Unit |
|---|---|---|
A | Meaning depends on selected mode: rate, part or original value | number |
B | Meaning depends on selected mode: base, whole or new value | number |
Step-by-step method
- Choose the percentage question that matches the problem.
- Enter A and B in the roles described by that mode.
- Apply the relevant formula.
- Keep the sign for percentage change so increases and decreases remain distinguishable.
Worked example
A user wants to calculate 20% of 250.
Example inputs
- Mode = What is A% of B?
- A = 20
- B = 250
Calculation / processing
20 / 100 = 0.200.20 x 250 = 50
The result is the portion represented by 20 percent of the base value 250.
Assumptions
- Inputs are treated as ordinary real numbers.
- Percentage change uses the absolute value of the original value in the denominator so the sign of the numerator indicates increase or decrease.
Limitations
- A percentage result is only meaningful when A and B represent comparable quantities for the selected question.
- Percentage change from an original value of zero is undefined in this model.
Common questions
What is the difference between percent of and percentage change?
Percent of finds a portion of a base. Percentage change compares a new value with an original value.
Why can percentage change be negative?
A negative result means the new value is lower than the original value.
Can I enter decimals?
Yes. The calculation engine accepts finite decimal values.
Methodology sources
This page uses basic mathematical or ToolLott implementation logic that does not require an external factual source. The worked result is still tied to the production tool and QA example.
Related ToolLott tools
A realistic way Alex could use this tool
Alex is a operations coordinator.
Alex is reviewing a supplier allowance and needs to confirm what 20% of a 250-unit budget line actually represents before approving the variation.
They use the worked values shown in the tool: Calculation: What is A% of B?; A: 20; B: 250.
ToolLott returns “20% of 250 = 50”. That gives Alex a concrete figure to check against the real task before they copy it into the next document or decision.
Fictional scenario using realistic example data. For Ready tools, the worked result is tied to the tested example shown in the tool. Replace the figures with your own inputs and independently verify important professional, financial, legal, health or safety decisions.
What this calculator is for
Use it to solve common percentage questions without manual arithmetic.
It sits within ToolLott’s Date & Time collection, where you can also calculate age, date differences and durations, or convert meeting times between worldwide cities and time zones.
Percentage Change & Comparison
Use one place for the common questions people actually ask: “what percent?”, “how much did it change?” and “what was the original?”