How is it different from percentage change?

Percentage change has a clear starting value and divides by that old value, so swapping the numbers changes the result. Percentage difference has no fixed starting point and divides by the average of the two values, so it is used when neither value is the reference.

When should I use percentage difference?

Use it when comparing two independent measurements where neither is the original, such as two quotes, two test results, or two prices for the same item. Use percentage change when one value clearly comes before the other, like an old price and a new price.

Percentage Difference Calculator

Find the percentage difference between two values. Unlike a percentage change, which compares a new value against an old one, percentage difference compares two values against their average, so the order does not matter. It is the right measure when neither number is the starting point, such as comparing two quotes, two prices, or two measurements.

First value

Second value

40%

Difference of 20, average of 50

The percentage difference formula

Percentage difference equals the absolute difference between the two values, divided by their average, multiplied by 100. In symbols, it is the size of (A minus B), divided by ((A plus B) divided by 2), times 100. Because it divides by the average, swapping A and B gives the same answer.

Worked example

Two builders quote $40,000 and $60,000 for the same job. The difference is $20,000 and the average is $50,000. So $20,000 divided by $50,000 is 0.4, which is a 40% difference between the two quotes.

Note this is not the same as saying one is 50% more than the other. That figure (percentage change from $40,000 to $60,000) uses the lower quote as the base.

Difference, change, or increase?

Percentage difference: two values, no starting point, divide by the average. Symmetric.
Percentage change or increase: an old value and a new value, divide by the old value. Direction matters.

Frequently asked questions

Why divide by the average?

Because neither value is the reference. Using the average treats both values equally, so the result is the same whichever way round you enter them.

When should I use percentage change instead?

When one value clearly comes first, such as an old price and a new price, or a starting weight and an ending weight.

Related calculators

Percentage Calculator: percentage change from an old value to a new value.
Percentage Increase Calculator: a rise from old to new.
Percentage of a Percentage Calculator: take a percentage of a percentage.

Calculate.co.nz is partnered with Interest.co.nz for New Zealand's highest quality calculators and financial analysis.

All calculators and tools are provided for educational and indicative purposes only and do not constitute financial advice.

Calculate.co.nz is proudly part of the Realtor.co.nz group, New Zealand's leading property transaction literacy platform, helping Kiwis understand the home buying and selling process from start to finish. Whether you're a first home buyer navigating your first property purchase, an investor evaluating your next acquisition, or a homeowner planning to sell, Realtor.co.nz provides clear, independent, and trustworthy guidance on every step of the New Zealand property transaction journey.

Calculate.co.nz is also partnered with Health Based Building and Premium Homes to promote informed choices that lead to better long-term outcomes for Kiwi households.

All content on this website, including calculators, tools, source code, and design, is protected under the Copyright Act 1994 (New Zealand). No part of this site may be reproduced, copied, distributed, stored, or used in any form without prior written permission from the owner.