About Sumwise

Sumwise is a small set of free calculators for three jobs: measuring and ordering materials for home and trade work, working out what marketplaces take from a sale, and converting creator payments into real money.

Who is behind it

I am a software developer who builds every calculator on Sumwise, writes the worked examples and checks each formula and fee rate against the official source before it goes live. When a platform changes a fee I update the page and date the change, so you can see exactly what the numbers are based on.

How every calculator is built

• The working is shown. Each result comes with the formula and your own numbers substituted in, so you can check it by hand.
• A worked example. Every page walks through one real calculation step by step. The same example is part of the calculator's automated tests.
• Sourced, dated rates. Any fee or rate links to the platform's or standard's own published page, with the date we last checked it. Fee pages keep a changelog.
• Regular re-checks. Every stored rate is re-verified against its source at least once a quarter.
• No invented numbers. If we can't find an official source for a figure, we don't publish the calculator that depends on it.

Found a mistake?

If a result looks wrong or a fee has changed, please tell us with the page and the numbers you entered. Corrections are dated on the page they affect.

Advertising

The calculators are free and paid for by advertising. Ads never change a result, and no platform pays to be included in or ranked by a comparison. See the privacy policy for how ads use cookies.