Find a percentage of a number, recover a missing value, compare percentage change or difference, and add or remove a percentage-based tax. Choose the section that matches your question; the formulas use different starting values.
Percentage Calculator
Provide any two values below and click Calculate to get the third.
Percentage Calculator in Common Phrases
Percentage Difference Calculator
Find the percentage difference between two values.
Percentage Change Calculator
See the percentage increase or decrease from an old value to a new value.
Tax / Percentage Add & Remove Calculator
Add tax (GST/VAT/sales tax) to a price, or work out the original price before tax.
Choose the right percentage calculation
A percentage means “per hundred”: 15% = 15 ÷ 100 = 0.15. The important part is identifying which number represents the whole.
| Question | Formula | Example |
|---|---|---|
| What is P% of a number? | P ÷ 100 × whole | 15% of 80 = 12 |
| One number is what percent of another? | part ÷ whole × 100 | 42 out of 50 = 84% |
| A known amount is P% of what total? | part ÷ (P ÷ 100) | 12 is 15% of 80 |
| How much did a positive starting value change? | (new − original) ÷ original × 100 | 100 to 120 = 20% increase |
| How different are two positive values? | |A − B| ÷ ((A + B) ÷ 2) × 100 | 100 and 120 differ by about 18.1818% |
How to enter your values
In the first calculator, enter any two values in the statement percentage % of whole = part and leave the unknown field empty. Click Calculate. Clear an old answer before solving a different missing value: if all three fields are filled, the percentage and whole fields are used to recalculate the part.
The common-phrase calculators answer the same questions with two dedicated inputs. Use the separate Change, Difference or Tax section for those tasks. Enter plain numbers and use consistent units on both sides of a comparison.
Calculate marks across subjects
For a straightforward marks total, add your earned marks and maximum marks separately, then calculate earned total ÷ possible total × 100.
For example, scores of 70, 80, 75, 85 and 90, each out of 100, add to 400 ÷ 500 × 100 = 80%. Enter 400 and 500 in the “is what % of” calculation.
Do not simply average subject percentages when their maximum marks differ. A score of 40/50 and a score of 50/100 combine to 90 ÷ 150 × 100 = 60%, although averaging 80% and 50% gives 65%. A school may instead apply course weights, exclusions or a separate grading policy; follow that policy for an official result. This tool does not convert a percentage into an official GPA.
Percentage change, difference and points
Change uses an original value as the baseline. Going from 80 to 60 is (60 − 80) ÷ 80 × 100 = −25%, a 25% decrease. Going back from 60 to 80 is a 33.3333% increase because the baseline is now 60.
Difference compares two positive values symmetrically, using their average as the baseline. Swapping those two values leaves the percentage difference unchanged. Use change when one value is a starting point and the other is a later result.
Percentage points measure subtraction between percentages. A rate rising from 4% to 6% rises by 2 percentage points, or by (6 − 4) ÷ 4 × 100 = 50% relative to the original rate.
Add tax or remove included tax
For a single stated rate r, adding tax means total = base × (1 + r ÷ 100). A base of 100 with a 20% rate gives 20 tax and a total of 120.
To remove tax already included in a total, divide: base = total ÷ (1 + r ÷ 100). From a total of 120 at 20%, the base is 100 and the tax is 20. Subtracting 20% of 120 would give 96, which is not the pretax base.
Choose the rate applicable to your transaction. The calculator performs the arithmetic; it does not determine tax eligibility, exemptions or the legally required rate.
Reverse a discount or increase
A sale price of 90 after 10% off represents 90% of the original. In the missing-total calculation, enter 90 as the part and 90 as the percentage: 90 ÷ 0.90 = 100. For a 10% increase, the new value represents 110% of the original.
For several discount types and a complete sale-price breakdown, use the Discount Calculator.
Questions and input limits
Can a percentage be greater than 100?
Yes. For example, 150 is 150% of 100. Whether a value above 100% is meaningful depends on the question; an ordinary exam score without extra credit has a different context from a sales increase.
What happens when the starting value is zero?
A relative change from zero is undefined because the formula would divide by zero. Report the absolute change instead. A percentage difference is also undefined when the average of the two values is zero.
Can I compare negative values?
The tool uses the absolute size of the original value for percentage change and the absolute average for difference. These conventions can be misleading when values cross zero. State the absolute amounts and the convention used, or use a method specified for your subject.
Why does my answer have several decimal places?
Some divisions do not end, such as one-third. Displayed results use up to four decimal places. Keep sufficient precision during the calculation and round the final answer to the level your task requires.