The most common percent task
“What is 8% of $250?” is the same skeleton as “What is 15% of last year’s revenue?” Once you see the pattern, you stop reaching for mysterious buttons and start reading the story.
The mechanics
To take p% of a number N: convert p% to a decimal (divide by 100), then multiply.
p% of N = (p / 100) × N Example: 8% of 250 = 0.08 × 250 = 20
Mental shortcuts that stay honest
- 10% is one-tenth: move the decimal left once.
- 5% is half of 10%.
- 1% is two orders of magnitude: move the decimal left twice.
Then compose: 15% = 10% + 5%; 18% ≈ 20% − 2×(1%).
Money examples
- Sales tax on a subtotal.
- A deposit or down payment expressed as a percent.
- A portfolio position size as a percent of net worth.
Sanity checks
If your answer is bigger than the original whole for a “percent of” problem under 100%, stop—unless you intended a percent greater than 100%.
Use the calculator
FAQ
- How do I find the original if I know the part?
Rearrange: if p% of N equals P, then N = P / (p/100), provided p ≠ 0. Our change lessons cover the related “percent increase” form.