What does this tool do
The Percentage Calculator computes percentages three ways: find X% of Y, find what percent X is of Y, or find the percentage change between two values. Each mode uses a closed-form formula and shows the result instantly. Ideal for discounts, tip calculations, growth rates, and proportions.
How to use it
- Select a mode — Choose one of the three calculation types at the top.
- Enter values — Type the numbers in the input fields. Each mode has two fields (e.g. X and Y, or From and To).
- View result — The tool computes and displays the answer with a human-readable label.
- Switch modes — Change mode anytime; the inputs and result update accordingly.
How it works
Three modes, each with a closed-form formula:
- X% of Y:
result = Y × X / 100 - X is what % of Y:
percent = (X / Y) × 100 - % change from X to Y:
change = ((Y − X) / |X|) × 100
For "what %" mode, Y cannot be zero. For "% change" mode, the starting value (X) cannot be zero. Invalid input shows an error message.
All calculations run entirely in your browser. No data is sent to any server.
Use cases & examples
- Discounts — What is 20% of $50? → $10
- ** proportions** — 25 is what % of 200? → 12.5%
- Growth — % change from 80 to 100? → 25%
- Tips — 15% of a $45 bill → $6.75
- Statistics — Share of total (e.g. 75 out of 100 → 75%)
Example
20% of 250 → 50
40 is what % of 160 → 25%
Change from 50 to 75 → 50%
Limitations & known constraints
- Division by zero — "What %" mode: Y cannot be 0. "% Change" mode: starting value cannot be 0.
- Numerical precision — Results are rounded to 6 decimal places.
- Two values only — Each mode accepts exactly two inputs; no batch or list calculations.