How we make sure your tax return is correct

We're often asked, "How can you be sure the app calculates my tax return correctly?" It's an important question with many layers. There is the initial tax knowledge by our tax advisors and the following translation into code-logic by our developers. But there is much more. Like making sure, updates or new features don't break older structures, preventing security lacks, and testing every feature on different levels. We are proud that Accountable is a product built and tested by a strong group of tax advisors and developers. Even though every one of them has their own responsibilities and specialization, the app is a product of real teamwork. There is Juan, for example, who built the VAT feature for Germany together with the input by our tax advisors Mira and Andreas. Jules on the other hand translated the complex income tax rules into a real feature. Melinda is responsible for the many levels of testing and Mokhtar is taking care of security tests.

Translating German tax rules into code

Our tax advisor partners were there from the very beginning. Having them on board is crucial to make sure, all tax regulations are correct and complete in the app. So, before our developers begin to work on a new feature, we sit down with our tax advisor partners who provide us with the knowledge of the official law and rules. A feature like the VAT return, for example, is developed together with our partners who are specialists in this field. Later on, once the feature is developed, they test and QA the app, trying to challenge the feature and check if the results they get are correct every time. Sometimes, this process can be quite challenging, because tax rules are not as fixed as they might seem. People often assume the tax law is strictly defined and regulated. But as you dive deeper into the topic, you realize there can be different interpretations and tax advisors often disagree. That's why we consult with several different partners to get the best understanding of difficult tax regulations.

A lot of testing and validation

Rejecting inconsistent data

Once we are sure the tax law and its regulations are translated into code, we have to ensure there is no room for mistakes. So, we built regulations that make sure that entered data is logical and compliant with the official rules. Should you, for example, select Reverse Charge for an invoice but also enter a VAT amount, the app knows something is wrong and will reject the input.

Regular and frequent testing

Running different types of tests not only for usability or functionality but also for correctness is a huge part of our development process. That's why we run automated tests every day to check the Accountable app for false input in the database. A crucial part play the so-called unit tests which examine the smallest fractions of the app. These tests decompose the codebase into little parts and check whether what you put in leads to the correct, expected output. For example, when you create a list of expenses and invoices you should get a certain amount. A unit test checks if the issued amount is correct. Thousands of those tests in the code are running several times a day, every time before we deploy the code. We also run similar tests, on the level of the features. These are called integration tests and check for errors between the single units. Finally, we run end-to-end tests which actually audit the frontend of the app, so the part the user sees. These tests verify that larger functions give the correct output. It checks, for example, if the VAT amount for a specific line in the VAT statement is computed correctly. We run automated as well as manual end-to-end tests, especially when we fix a bug or set live a new feature. Also crucial for us are regression tests, which ensure that nothing in the old code breaks when we add new features. Sometimes there can be unplanned, unpredictable consequences when deploying new code. For example, when you change something related to the income tax feature but don't realize it's breaking the VAT feature. Without a regression test running on the entire app, you might not see these errors as fast and early. In the end, every time we deploy a new feature we test them manually with real user cases, once in the app and once with our tax advisors. Only when every result the app calculates corresponds with the results of our tax advisors, we set live the feature.

IT security audits

Other very important and related procedures are the security audits that happen every year. Accountable is an official regulated financial institution, so we are subject to government audits and controlled by the BaFin. We also have regular IT security audits by security consultants who try to find and hack security breaches in our system. Luckily, this has never happened.

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Author - Sophia Merzbach

Sophia has been a key member of the Accountable team for many years, bringing a unique blend of journalistic precision and in-depth tax expertise to her work.

Who is Sophia ?

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They always answer right away to any question I have, they provide clear answers, and they are very patient even when I struggle to understand. They try to explain in different ways. They are very helpful, responsive and friendly.

Chiara Marradi

10/05/2026

This is an amazing application with great support on issues. In short as in day I am addicted to it (in a positive way). I myself is from IT project management and the way they have captured the user requirement, it’s phenomenal.

Sumit Tewary

01/12/2024

UI is great. Feature packed and very easy to use. The team at Accountable were VERY quick to respond and their team of technicians soon had a fix in place. Very happy with the level of service so far. Thumbs up from me!

Dean Osborne

05/06/2023

Everything was great! All my questions were answered quickly and in a friendly manner.

Wenzeslawa Wegener

11/05/2026

This program is a lifesaver, and it is always improving. Plus, it has an AI chat feature that is actually useful.

Jeffrey Humble

12/01/2026

The coaching session on tax management was excellent, good material, excellent explanations and very insightful. Combined with the AI I never feel alone with Accountable.

Sergio Barbarino

13/04/2026

The availability of your team to help and guide people to understand their finances better is what really makes Accountable valuable. While the AI is able to give answers to most basic questions, specific scenarios need counsel from a human which your team performs beautifully.

Norma

06/04/2026

Fast and careful answers from Alina. Top service. Thank you.

Anonymous

06/04/2026

In the world where everyone seems to be out to get small entrepreneurs and overwhelm them with new rules, more taxes and reporting obligations, Accountable often feels like the one steady partner that actually wants you to succeed, providing quick, clear and personalised support. Thank you!

Janina Arsenjeva

10/04/2026

They always answer for questions wherever is via direct e-mail or through app. If they can’t answer fully they will forward you to the right place. Documents were always prepared well and ready to send further to government. Everything is intuitive in the app and easy to sort out even for someone completely green in this field.