Percentage Calculator
Three percentage questions, one page — portions, shares and change, all computed as you type.
① What is X% of Y?
② X is what % of Y?
③ Change from X to Y
How to use
- Scroll to the panel that matches your question.
- Type your numbers — results update instantly.
- Use the change panel to measure growth or decline between two values.
Frequently asked questions
What are the three modes?
① "X% of Y" finds a portion of a number (15% of 200 = 30). ② "X is what % of Y" finds the share (30 is 15% of 200). ③ "Change from X to Y" finds the percentage increase or decrease between two values (150 → 180 is a 20% increase).
How is a percentage change computed?
As (new − old) ÷ |old| × 100. The absolute value in the denominator keeps decreases reporting correctly when the starting value is negative, and the result is labeled Increase or Decrease so the direction is never ambiguous.
Why can "X is what % of Y" fail?
When Y is zero the share is undefined — nothing can be a percentage of nothing, so the tool shows a dash instead of inventing a number. Negative values are allowed and computed normally.
How precise are the results?
The math is done in full floating-point precision and only the display is trimmed to 6 significant digits, so a result like 33.333333% shows as 33.3333% without losing practical accuracy.
Is anything sent to a server?
No. Every calculation runs locally in your browser as you type.