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Web product
Added November 14, 2026
About the product
Toggle9 is a free collection of 200+ calculators, unit converters and printables for everyday numbers: what a paycheck comes to after tax, how much concrete to order, what 180°C is in Fahrenheit, or how a mortgage splits between interest and principal. What makes it different: • Shows the math. Every calculator lays out the working step by step, so you can check the answer instead of trusting a black box. • Cites its sources. Tools are built from official references such as the IRS, HMRC and NIST. Over 1,400 sources are cited across the site, each listed on the tool's own page. • Tested before it goes live. 700+ automated tests compare results with answers worked out from those sources. Each tool is also checked in Chrome and Safari, on phone and desktop, with an accessibility scan. • Runs in your browser. The maths happens on your device, so amounts, dates and names you type aren't sent to Toggle9 or anyone else. • Free, with no sign-up. Nothing to install and no account. Categories include money (salary and paycheck, mortgages and loans, investing and retirement, budgeting, business), health and fitness, home and yard, kitchen and cooking, date and time, car and workshop, languages, and printables such as graph paper, multiplication worksheets and coloring pages. For website owners: 180+ of the calculators can be embedded free on any site, with no cookies or tracking inside the embed. Built and checked by Jeremiah Say, a software developer, data scientist and former maths tutor based in Singapore. Corrections are published openly at toggle9.com/corrections/.
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