About us



The essential blend of expertise to keep you compliant

SDC Testing is the product of a collaboration between two trusted contractor brands. Contractor Calculator and Qdos share more than 30 years’ experience working with contractors.

Between us, we have the expertise to make sure your umbrella solution stays fully compliant with HMRC’s travel and subsistence expenses rules, exonerating you from unnecessary tax liabilities as a result.

With more than 20 years of software development experience, and know-how in crucial areas such as employment case law, our SDC testing tool promises to be the most efficient and accurate solution on the market.



ContractorCalculator was originally created in 1999 to help contractors navigate the IR35 tax legislation. It then evolved into a multifaceted resource hub and is now the UK’s leading website for the contingent workforce, attracting well over 100,000 ABC audited visitors per month.

As well as a comprehensive range of free online financial, salary and tax calculators, we also provide expert commentary and analysis from a range of tax and industry leaders. Meanwhile, our unique Online IR35 Test has been taken over 90,000 times.

Keeping our finger on the pulse of the contracting sector has helped us to develop in-depth knowledge of SDC, which we have used to create this comprehensive compliancy tool.



With more than 15 years’ experience working alongside contractors, Qdos has an extensive background providing insurance and tax advice for the contingent workforce. This, along with our strong commitment to staying fully up-to-date with IR35 developments, means we are well-versed when it comes to SDC and relevant legislation.

Our unique blend of tax, business compliance and legal acumen means we are exceptionally well-equipped to safeguard your umbrella solution from tax liabilities.

Meanwhile, our expert knowledge of employment case law has been particularly essential in ensuring we have been able to help develop the most accurate SDC testing solution possible.

How do I get started with SDC Testing?

With potentially thousands of contractors on your books, you’ll have little time to waste. Getting started with us couldn’t be any more straightforward.

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