How to use it
- Enter Percent (X).
- Enter Value (Y).
The formula
X% of Y = X ÷ 100 × Y.
Worked example
15% of 80 is 12; and 12 is 15% of 80.
About this calculator
Percentages are the most-used and most-misused arithmetic in money: discounts, tips, taxes, raises, interest — all of it. The two directions ('X% of Y' and 'X is what % of Y') cover nearly every daily case, so this tool computes both at once.
The classic trap is reversing a percentage: a 20% discount followed by a 20% increase does not return to the start (100 → 80 → 96). Whenever you undo a percentage, divide instead of multiplying — the FAQ shows the pattern.
Frequently asked questions
How do I add a percent to a number?
Multiply by (1 + percent/100): adding 15% to 80 gives 92.
How do I work backwards from a total?
Divide by (1 + percent/100): if 92 includes 15%, the base was 80.
Percent vs percentage points?
Going from 10% to 12% is a rise of 2 percentage points, but a 20% relative increase.
Tips
- Automate the boring parts of your budget.
- Compare unit prices, not package prices.
- Small recurring costs add up over a year.
Key terms
- Net worth
- Assets minus liabilities.
- Budget
- A plan for income and spending.
- Unit cost
- Price per single unit.