Percentage Calculator
Every common percentage calculation in one place - instant results as you type.
What is X% of Y?
Percentage Formulas
- X% of Y = (X / 100) x Y. Example: 15% of 200 = 30.
- X is what % of Y = (X / Y) x 100. Example: 30 is 15% of 200.
- % Change = ((New - Original) / |Original|) x 100. Shows increase or decrease.
- % Difference = (|X - Y| / Average(X, Y)) x 100. Symmetric - the order does not matter.
- Add X% to Y = Y x (1 + X/100). Common for adding GST, markups, or tips.
- Subtract X% from Y = Y x (1 - X/100). Common for discounts and reductions. Note: subtracting 10% then adding 10% does NOT return to the original value.
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Percentage calculations for everyday business use
Percentages are everywhere in business - profit margins, discount rates, tax calculations, year-over-year growth, staff utilisation rates, and budget variances. While the maths is straightforward, it is surprisingly easy to mix up percentage change and percentage difference, or to forget that subtracting 10% then adding 10% does not get you back to the original number.
This calculator covers the six most common percentage operations. "What is X% of Y" handles tax calculations and markups. "X is what % of Y" answers questions like "what percentage of our revenue goes to COGS?" Percentage change measures growth or decline between two periods. Percentage difference gives you a symmetric comparison between any two values. And the add/subtract functions handle GST, discounts, and markups directly.
A common trap: 10% GST added to $100 gives $110. But if someone tells you the GST-inclusive price is $110 and you subtract 10%, you get $99 - not $100. To extract GST from an inclusive price, divide by 1.1 instead of subtracting 10%. These kinds of rounding and reversal errors add up across thousands of invoices.
How to use this percentage calculator
- Choose the operation: Select from six tabs - "X% of Y", "X is what % of Y", percentage change, percentage difference, add a percentage, or subtract a percentage.
- Enter your values: Type the numbers into the input fields. Results update instantly as you type - no need to press a calculate button.
- Read the result and formula: The calculator shows both the answer and the formula used, so you can verify the logic and replicate it in spreadsheets or accounting software.
Percentage calculations in Australian tax and GST
GST is the most common percentage calculation in Australian business. Adding 10% GST to $100 gives $110, but extracting GST from $110 requires dividing by 11 (not subtracting 10%). The GST component of a GST-inclusive amount is always 1/11th of the total, not 10%. This distinction matters for BAS preparation - claiming 10% of a GST-inclusive figure instead of 1/11th overstates your input tax credits and can trigger ATO audit attention. Other common percentage operations include calculating PAYG withholding rates, superannuation guarantee contributions (currently 11.5%), and early payment discounts expressed as annual percentage rates.
How does AP automation eliminate percentage errors?
When invoices are processed manually, GST calculations, discount percentages, and tax withholding rates are all opportunities for human error. Pulsify extracts line items, tax amounts, and totals automatically, cross-checks the maths, and flags discrepancies before they reach your ledger.
See how Pulsify automates AP →Eliminate manual calculation errors in AP
Pulsify automates AP from inbox to ledger - invoice capture, coding, approval workflows, and sync to Xero or MYOB.