--- title: "The API is the product: how Certino plugs into the systems you already use" description: Certino's calculations are built API-first, so HR systems, mobility platforms and payroll providers can add hypo tax, gross-up and shadow payroll calculations without changing how they work. image: https://www.certino.com/hubfs/the-api-the-product-cover.png --- [Skip to content](https://www.certino.com/blog/the-api-the-product#main-content) [![Certino Ltd. Logo](https://www.certino.com/hubfs/march-2021/globals/certino.svg)](https://www.certino.com/) ![](https://cdn2.hubspot.net/hubfs/234700/_nov_2019/globals/nav.svg) - [Home](https://www.certino.com) - [Platform](https://www.certino.com/platform) - [Managed service](https://www.certino.com/managed-service) - [About us](https://www.certino.com/about-us) - [Blog](https://www.certino.com/blog) - [Book a call](https://www.certino.com/book-a-consultation) [Blog](https://www.certino.com/blog)  /  [Technology](https://www.certino.com/blog/tag/technology) # The API is the product: how Certino plugs into the systems you already use ![](https://www.certino.com/hubfs/aaron-parfitt-no-shadow.jpeg) [Aaron Parfitt](https://www.certino.com/blog/author/aaron-parfitt) • 7 October 2022 • 3 min read ![The API is the product: how Certino plugs into the systems you already use](https://www.certino.com/hubfs/the-api-the-product-cover.png) Most businesses that deal with international employees already have their systems in place. An HR system, a mobility platform, a payroll provider, maybe a tax adviser's tools. The last thing they want is another product that forces them to change how they work. That's why we built Certino API-first. Our calculations aren't locked inside our own screens. They're available through an API, so they can run inside the systems you already use. ### What Stripe got right Before Stripe, taking payments online meant wrestling with complicated, badly documented interfaces. Stripe didn't make payments less complex. It hid that complexity behind a simple, well-designed API that developers could plug in quickly. That's why it became one of the most widely used payment APIs in the world. Shadow payroll has the same shape of problem. The rules are complex: tax rates, social security, treaties, gross-ups, and currency conversion, all changing every year and different in every country. But what most systems need from those rules is simple: the right number, with the workings to back it up. ### What the Certino API does The Certino API gives your system the same calculations our own platform uses: - **Hypo tax:** what the employee would have paid at home. - **Gross-ups:** the extra pay needed when the employer covers the tax. - **Shadow payroll figures:** payroll-ready numbers for the host country. - **The workings:** a clear breakdown for each figure, so anyone can check how it was reached. You send the inputs, and you get back consistent results. The same inputs always give the same answer. ### Who it's for - **Mobility and HR platforms** that want to offer accurate tax calculations without building and maintaining country tax engines themselves. - **Payroll providers** that need reliable shadow payroll figures for international employees. - **Advisory firms** that want to run calculations for many clients from their own tools. - **Large employers** with their own internal systems who want calculations to happen automatically, as part of their existing process. Our [partnership with Topia](https://www.certino.com/blog/certino-and-topia-partner-to-deliver-connected-global-compensation-workflows) is one example: Certino's calculations run within Topia's workflows, so their clients get the results without switching tools. ### Built to be relied on An API is only useful if you can depend on it. We design ours to be secure, available and able to grow with you, and our security is independently audited against ISO 27001 and SOC 2. Every country engine is tested and updated as the rules change, so the numbers you get are current. ### Platform or API: your choice Some teams prefer to work in the Certino platform. Others want the calculations inside their own systems. Many use both. Either way, it's the same engine, the same rules and the same answers. ### Talk to us about integrating If you'd like to explore connecting to the Certino API, [book a call with our team](https://www.certino.com/book-a-consultation). Share [mailto:?subject=The+API+is+the+product%3A+how+Certino+plugs+into+the+systems+you+already+use&body=https%3A%2F%2Fwww.certino.com%2Fblog%2Fthe-api-the-product](mailto:?subject=The+API+is+the+product%3A+how+Certino+plugs+into+the+systems+you+already+use&body=https%3A%2F%2Fwww.certino.com%2Fblog%2Fthe-api-the-product) ![](https://www.certino.com/hubfs/aaron-parfitt-no-shadow.jpeg) ### Aaron Parfitt Aaron is Head of Engineering at Certino, where he leads the team that builds and runs the platform and the country tax engines behind every calculation. He focuses on making Certino's calculations fast, secure and reliable, whether clients use the platform or connect through the API. He's based in Cardiff, UK. [← All articles](https://www.certino.com/blog) ## More from the Certino blog [![alt](https://www.certino.com/hubfs/budget-2026-post-budget-brief-cover.png)](https://www.certino.com/blog/budget-2026-one-budget-two-payrolls) 28 October 2026   |   [Compliance](https://www.certino.com/blog/tag/compliance), [Global Mobility](https://www.certino.com/blog/tag/global-mobility), [International Tax](https://www.certino.com/blog/tag/international-tax), ##### [Budget 2026: one Budget, two payrolls](https://www.certino.com/blog/budget-2026-one-budget-two-payrolls) [![alt](https://www.certino.com/hubfs/six-signs-managed-shadow-payroll-cover.png)](https://www.certino.com/blog/six-signs-its-time-for-a-managed-shadow-payroll-service) 13 October 2026   |   [Shadow Payroll](https://www.certino.com/blog/tag/shadow-payroll), [Process Change](https://www.certino.com/blog/tag/process-change), ##### [Six signs it’s time for a managed shadow payroll service](https://www.certino.com/blog/six-signs-its-time-for-a-managed-shadow-payroll-service) [![alt](https://www.certino.com/hubfs/where-ai-shouldnt-do-the-maths-cover.png)](https://www.certino.com/blog/why-we-dont-let-ai-do-our-maths) 09 October 2026   |   [Shadow Payroll](https://www.certino.com/blog/tag/shadow-payroll), [Technology](https://www.certino.com/blog/tag/technology), ##### [Why we don’t let AI do our maths](https://www.certino.com/blog/why-we-dont-let-ai-do-our-maths) Book a call ## Talk to a shadow payroll specialist A short call to look at how you run shadow payroll today and where Certino fits. No obligation. [Book a call](https://www.certino.com/book-a-consultation) Your payroll data, properly protected Independently audited security, built for sensitive pay data. ![ISO 27001:2022](https://www.certino.com/hubfs/march-2021/globals/iso-27001.png) ISO 27001:2022 ![AICPA SOC 2](https://www.certino.com/hubfs/march-2021/globals/aicpa.png) SOC 2 audited ![GDPR](https://www.certino.com/hubfs/march-2021/globals/eu-gdpr.png) GDPR compliant ![certino-white](https://www.certino.com/hubfs/march-2021/globals/certino-white.svg) ###### Links - [Shadow payroll guide](https://www.certino.com/shadow-payroll) - [Siemens case study](https://www.certino.com/siemens) - [Platform](https://www.certino.com/platform) - [Managed shadow payroll](https://www.certino.com/managed-service) - [Research & insights](https://www.certino.com/blog) - [Book a demo](https://www.certino.com/book-a-consultation) ###### Contact - [+44 (0) 207 118 1405](tel:+44(0)2071181415) - [enquiries@certino.com](mailto:enquiries@certino.com) - [![linkedin](https://www.certino.com/hubfs/linkedin.svg)](https://www.linkedin.com/company/certino/) © 2026 Certino Ltd. 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