Percent Calculator
Enter a value and a percent once to see four useful answers at the same time: the percent of the value, the value increased by that percent, the value decreased by that percent, and the original total that would make your value equal to that percent. The result cards update instantly and show the arithmetic behind each answer.
How to use the percent calculator
-
1
Enter the value
Type the amount, price, score, total, or any other base number you want to work with.
-
2
Enter the percent
Add the percentage as a plain number, such as 15 for 15% or 7.5 for 7.5%.
-
3
Read the four cards
See percent of value, increase by percent, decrease by percent, and reverse percent from the same inputs.
-
4
Copy or adjust
Use the result in your note, invoice, spreadsheet, or report, then tweak the numbers for another scenario.
Quick examples
| Question | Calculation | Result |
|---|---|---|
| 15% of 80 | 80 x 0.15 | 12 |
| Add 8% to 120 | 120 x 1.08 | 129.6 |
| Take 20% off $85.00 | $85.00 x 0.80 | $68.00 |
| 18 is 6% of what | 18 x 100 / 6 | 300 |
| 7.5% of 48 | 48 x 0.075 | 3.6 |
| Reduce 500 by 12% | 500 x 0.88 | 440 |
Formulas the tool uses
Where value is the number in the Value box and percent is the number in the Percent % box:
- Percent of value:
value * percent / 100 - Increase by percent:
value * (1 + percent / 100) - Decrease by percent:
value * (1 - percent / 100) - Value is percent of what:
value * 100 / percent
The reverse calculation needs a non-zero percent. If the percent is 0, there is no finite original value that can make the entered value equal to 0%.
Percent vs decimal
A percent is a decimal ratio written on a 100-point scale:
- 50% = 0.5
- 12.5% = 0.125
- 200% = 2
- 0.4% = 0.004
Multiplying by a percent is the same as multiplying by its decimal form. For example, 80 * 0.15 = 12, so 15% of 80 is 12. This is also a quick sanity check: 350% of 40 cannot be 14, because 3.5 times 40 is 140.
Watch out for
- Sequential discounts are not additive. A 20% discount followed by another 10% discount is 28% off overall, not 30%, because the second discount applies to the new price.
- Percentage points are different from percent change. A rate moving from 5% to 7% rises by 2 percentage points, but the relative increase is 40%.
- Currency results may need rounding. The math can return more decimal places than a receipt or invoice can show, so round only after the calculation.
Frequently Asked Questions
The Percentage Calculator focuses on separate classic question formats. This percent calculator keeps one value and one percent on screen, then shows percent-of, increase, decrease, and reverse-percent answers together.
Yes. A negative percent reverses the direction of increase and decrease. For example, increasing 200 by -15% gives 170, while decreasing 200 by -15% gives 230.
The reverse card is left blank because division by zero is undefined. A value cannot be a finite 0% share of another number unless the value is also zero.
Use decimals such as 0.5 or 3.75. The calculator does not parse fractions like 1/4, so convert the fraction to 0.25 first.
No. The calculations run in your browser, and the numbers you type stay on your device.
Related Tools
BMI Calculator
Calculate body mass index from height and weight. Shows WHO category, healthy-weight range and limitations of BMI.
GPA Calculator
Calculate grade point average from letter grades and credit hours. Supports US 4.0 and 5.0 honors scales with the standard A/B/C/D letter table.
Inflation Calculator
Calculate the equivalent purchasing power of a dollar across any two years using historical CPI data from 1913 to today.
Scientific Calculator
Full scientific calculator with trig, log, exponents, factorial, memory, parentheses and DEG/RAD toggle. Runs in your browser.
Binomial Probability Calculator
Compute exact, cumulative and tail probabilities for a binomial distribution. Enter n trials, p success rate and k successes.
Calorie Calculator
Estimate daily calorie needs for your goal using Mifflin-St Jeor BMR and activity factors. Includes deficit and surplus targets.