Percentage Calculator
Work out percentages, increases and discounts.
Your numbers
Your result
30
20% of 150
20% of 150
30
Remaining
120
- Percentage as a decimal
- 0.2
- 150 + 20%
- 180
- 150 − 20%
- 120
How it is worked out
- 20 ÷ 100 = 0.2
- 0.2 × 150 = 30
Common percentages of 150
A quick look-up for the percentages people use most, worked out from the number above.
| Percent | Amount | Add it | Take it off |
|---|---|---|---|
| 5% | 7.5 | 157.5 | 142.5 |
| 10% | 15 | 165 | 135 |
| 15% | 22.5 | 172.5 | 127.5 |
| 20% | 30 | 180 | 120 |
| 25% | 37.5 | 187.5 | 112.5 |
| 30% | 45 | 195 | 105 |
| 40% | 60 | 210 | 90 |
| 50% | 75 | 225 | 75 |
| 75% | 112.5 | 262.5 | 37.5 |
Percentage Calculator Math Formula
"Percent" means out of 100, so 20% is the same as 20 ÷ 100 = 0.20. Every percentage question is a small variation of that one idea. Here are the five formulas the calculator uses, each worked through with real numbers.
1. What is X% of Y?
Result = (X ÷ 100) × Y
Example: what is 20% of 150?
20 ÷ 100 = 0.2
0.2 × 150 = 30
So 20% of 150 is 30. A handy shortcut: 10% is the number divided by 10, so 10% of 150 is 15, and doubling it gives 20%.
2. X is what percent of Y?
Percent = (X ÷ Y) × 100
Example: 30 is what percent of 150?
30 ÷ 150 = 0.2
0.2 × 100 = 20%
So 30 is 20% of 150. Use this for test scores, such as 42 out of 50 marks, or for the share one item has of a total.
3. Percent change from X to Y
Change % = ((New − Old) ÷ Old) × 100
Example: a price goes from 80 to 100.
100 − 80 = 20
20 ÷ 80 = 0.25
0.25 × 100 = +25%
A positive answer is an increase and a negative answer is a decrease. Notice the order matters: going back from 100 to 80 is a -20% drop, not 25%, because the percentage is always measured against the starting value.
4. Add or subtract a percentage
Increase: Y × (1 + X ÷ 100)
Decrease: Y × (1 − X ÷ 100)
Example: add 15% to 200, such as a price plus tax.
15% of 200 = 30
200 + 30 = 230
Taking 15% off instead, such as a discount, gives 200 − 30 = 170. Be careful: a 10% rise followed by a 10% fall does not bring you back, because the second 10% is taken from a bigger number. 100 becomes 110, then 99.
5. Find the whole when you know a part
Whole = (Part ÷ Percent) × 100
Example: 30 is 20% of what number?
30 ÷ 20 = 1.5
1.5 × 100 = 150
So 30 is 20% of 150. This is how you find the original price when you only know the discount, or the full amount when you know what a share is worth.
Online Percentage Calculator
Our free online percentage calculator answers the five percentage questions people ask most. Find a percent of a number, work out what percent one number is of another, measure the percent change between two values, add or subtract a percentage, and find the whole number when you only know a part and its percentage. Pick a question, type two numbers and the answer appears instantly, with the working shown step by step.
Use it for discounts and sales prices, tips and tax, marks and grades, salary hikes, price rises, profit and loss, interest rates, test scores and everyday maths. It works with decimals and negative numbers, runs in your browser, needs no sign-up and works on phones, tablets and desktops.
Features Of ToolVega Percentage Calculator
- Five calculators in one: percent of, what percent, percent change, add or subtract %, find the whole
- Instant answer as you type, with a clear example already filled in
- Step-by-step working so you can see how the answer is reached
- Visual bar showing the share or the change at a glance
- Quick buttons for common percentages like 5%, 10%, 15%, 20%, 25% and 50%
- Quick-reference table for a number at 5% to 75%
- Works with decimals and negative numbers
- Helpful messages instead of errors, for example when dividing by zero
- Free, no sign-up, works on phone, tablet and desktop
- Private: calculated in your browser, nothing is stored
Frequently asked questions
How do I calculate a percentage of a number?
Divide the percentage by 100 and multiply by the number: (X ÷ 100) × Y. For example, 20% of 150 is 20 ÷ 100 × 150 = 30. For a quick estimate, 10% is the number divided by 10, and 50% is half of it.
How do I work out percent change or percentage increase and decrease?
Subtract the old value from the new value, divide by the old value and multiply by 100: ((New − Old) ÷ Old) × 100. A rise from 80 to 100 is (100 − 80) ÷ 80 × 100 = 25% up. A positive result means an increase and a negative result means a decrease. The change is always measured against the starting value, so going back down from 100 to 80 is a -20% fall, not 25%.
How do I add or subtract a percentage, such as a discount or tax?
To add a percentage, multiply by (1 + X ÷ 100). To subtract it, multiply by (1 − X ÷ 100). Adding 15% to 200 gives 200 × 1.15 = 230, and taking 15% off gives 200 × 0.85 = 170. This works for sale discounts, sales tax, VAT, GST, tips and service charges in any currency.
How do I find the original price or whole number before a percentage?
Divide the part by its percentage and multiply by 100: (Part ÷ Percent) × 100. If 30 is 20% of a number, the number is 30 ÷ 20 × 100 = 150. To undo a discount, do not just add the percentage back. If a sale price is 80 after 20% off, the original is 80 ÷ 80 × 100 = 100, not 96.
What is the difference between a percentage and a percentage point?
A percentage point is the plain difference between two percentages, while a percent change compares them as a ratio. If an interest rate rises from 4% to 5%, it has gone up by 1 percentage point, but that is a 25% increase in the rate, because 1 ÷ 4 × 100 = 25. Mixing the two up is a common reason news headlines and reports look confusing, so check which one is meant before you compare numbers.