About the Percentage Calculator
What is the Percentage Calculator?
A percentage is a number expressed as a fraction of 100 — “per cent” literally means “per hundred”. 18% means 18 out of every 100, or 0.18. Percentages make it easy to compare quantities of different sizes, which is why they are used for discounts, GST, exam marks, interest rates, election results and growth figures.
This calculator answers the seven percentage questions people ask most: P% of a value, what percent one number is of another, the percentage change from an old to a new value, increasing or decreasing a value by a percentage, finding the original whole from a part (reverse percentage), and the percentage difference between two values.
How to use the Percentage Calculator
- What do you want to find? — pick the question you want answered; only the fields that mode mentions are used. (sample: P% of X)
- Value (X) — the whole, original or starting value. (sample: 1,000)
- Percentage (P %) — the rate, for example 18 for 18% GST. (sample: 18)
- Part (Y) — a portion of X, used by the “what %” and reverse modes. (sample: 180)
- New Value — the later value, used for % change and % difference. (sample: 1,180)
- Press Calculate Percentage (results also refresh as you type). The result card shows the Percentage Result, along with Remaining 82%, X plus P% and X minus P%.
Formula used
P% of X = X × P ÷ 100
- X = the whole, original or starting value
- P = the percentage
- Y = a part of X
- New = the later value after a change
The other modes rearrange the same idea: Y as % of X = Y ÷ X × 100; % change = (New − X) ÷ |X| × 100; increase by P% = X × (1 + P/100); decrease by P% = X × (1 − P/100); reverse % = Y ÷ (P/100); % difference = |X − New| ÷ ((X + New) ÷ 2) × 100.
Worked example
These are the sample values already filled in the calculator above, and the result it returns for them:
| Input | Sample value |
|---|---|
| What do you want to find? | P% of X |
| Value (X) | 1,000 |
| Percentage (P %) | 18 |
| Part (Y) | 180 |
| New Value | 1,180 |
| Result | Value |
|---|---|
| 18% of 1,000 | 180 |
| Remaining 82% | 820 |
| X plus P% | 1,180 |
| X minus P% | 820 |
Quick percentage shortcuts
| Percentage | Shortcut | Example on 5,000 |
|---|---|---|
| 1% | Divide by 100 | 50 |
| 5% | Half of 10% | 250 |
| 10% | Divide by 10 | 500 |
| 12.5% | Divide by 8 | 625 |
| 20% | Divide by 5 | 1,000 |
| 25% | Divide by 4 | 1,250 |
| 50% | Divide by 2 | 2,500 |
Tips for using the Percentage Calculator
- A percentage increase followed by the same percentage decrease does not bring you back to the start: 100 + 10% = 110, but 110 − 10% = 99.
- To remove 18% GST from a tax-inclusive price, use the reverse mode with P = 118: the answer is the price before tax.
- A move from 8% to 9% is a rise of 1 percentage point but a 12.5% increase — keep the two ideas separate.
- Use percentage difference when neither value is the “before”; use percentage change when one value is clearly the starting point.