Percentage Calculator

Percentages without the second-guessing

Almost every percentage question in daily life is one of three shapes. Once you can spot which shape you are looking at, the arithmetic stops being intimidating and the calculator simply saves you time.

The three questions this tool answers

1. 1What is X% of Y? The discount, the tip, the tax, the commission. Multiply Y by X and divide by 100.
2. 2X is what percent of Y? Your score out of a total, your share of a bill, a conversion rate. Divide X by Y and multiply by 100.
3. 3What is the percentage change from X to Y? A price rise, a traffic drop, a salary bump. Subtract, divide by the original value, multiply by 100.

The third one is where mistakes cluster, because the answer depends entirely on which number you treat as the starting point. Going from 40 to 50 is a 25% increase. Going from 50 back to 40 is a 20% decrease. Same gap, different base, different percentage.

How to use the calculator

Choose the tab that matches your question, fill in the two values and read the result underneath. Each mode also shows the expression it used, so you can check the logic rather than trusting a number that appeared out of nowhere. Nothing needs to be submitted - results update as you type.

Everyday situations where it helps

• Shopping. A 30% discount on 89.99, then working out whether the second sale price is genuinely better.
• Salary and raises. Turning an offer of "a 6% increase" into an actual monthly figure.
• Study. Converting 47 correct answers out of 60 into a percentage you can compare with a grade boundary.
• Business reporting. Month-on-month growth, churn rate, margin on a product.
• Personal finance. How much of your income goes to rent, or how much a subscription increase costs over a year.

The percentage traps worth knowing

Percentages do not simply add up

A 20% rise followed by a 20% fall does not bring you back to where you started. Start at 100, rise to 120, then fall by 20% of 120, which is 24, and you land on 96. The second percentage is taken from a larger base, so it removes more than the first one added.

Percentage points are not percentages

If an interest rate moves from 4% to 5%, that is a rise of one percentage point, but a 25% increase in the rate itself. Headlines routinely mix the two, and the difference is large enough to change what a story means.

Stacked discounts multiply

A 50% discount plus an extra 20% off at checkout is not 70% off. The second discount applies to the already reduced price, so you pay 0.5 x 0.8 = 0.4 of the original - a 60% saving.

Converting between fractions, decimals and percentages

A percentage is just a decimal with the point moved two places. Recognising a handful of these pairs makes mental estimates fast enough that you can sanity-check any calculator, including this one.

Related calculators

For restaurant maths, the Tip Calculator applies a percentage and splits the bill in one step. If you are comparing weight or measurement changes, the BMI Calculator and the Unit Converter pair naturally with percentage change. And the Age Calculator is the tool you want when a percentage question involves dates rather than amounts.