About Theo

As a freelance conversion specialist, Theo has helped 170+ customers (such as Accenture, Greenchoice, and Nike) in 10+ countries to improve their websites.

He has been building and optimizing websites and web shops for more than 20 years. This means that he is one of the most experienced conversion specialists in the Netherlands.

Freelance conversion specialist at screen
Conversion optimization consultant on stage
Conversion specialist Theo van der Zee

Education and experience

Theo has many years of experience as a professional web developer. This ensures that he knows in detail how websites work technically and that he can easily discuss technical improvement points with developers. He also has a keen eye on human behavior. Thanks to his university master's degree in organizational psychology, he is well acquainted with scientific literature on psychology, statistical methods, and how to conduct research that is reliable and valid.

The combination of the above factors has already provided its customers with many millions of euros in added turnover from their website or webshop.

Theo has also written for parties such as Emerce and FrankWatching. As a conversion optimization specialist, he was also a speaker at dozens of national and international conferences, including Conversion Conference and Meet Magento.

Theo in numbers:

  • 75+ expert reviews conducted
  • 500+ A/B tests performed
  • Gave 25+ event presentations
  • Won 5+ web design awards
  • 250+ hours of training provided

Collaboration with customers

As a senior conversion specialist, Theo has now worked for clients in almost all industries. The clients (who hire him to support, or completely outsource, conversion optimization) vary in size from sole proprietorships to multinationals and everything in between. He also has extensive experience in optimizing websites for different target groups such as ecommerce, B2B, leadgen, sustainable, and small businesses.

As can be seen from the testimonials, customers are very satisfied with Theo as a freelance consultant. Properties that are regularly mentioned in the testimonials:

  • Enthusiastic
  • Clear
  • Honest
  • Direct


Because conversion optimization is a broad field, almost every conversion optimization specialist has his or her own ideas about the best principles to get the maximum result from a collaboration.

Connecting to the organization

Every organization has a different level of 'digital maturity'. Connecting to this is very important. For example, a website analysis is often better suited to a slightly less mature website and A/B testing is usually better suited to a more mature website. Issues such as available employees and budgets also play a role in which activities will yield the greatest return.

Communicate clearly

Successful conversion optimization is created by collaboration between several people. Consider, for example, managers, developers, analysts, and psychologists. Clear communication between these different people is therefore necessary to achieve the best results.

Thinking from the visitor's perspective

Ultimately, it is the visitor who decides whether or not to make a purchase, request or donation. This is why it is important to think from the visitor's perspective and stay away from 'tricks' to entice them to convert. Things like user tests can help with this.

Working with an eye for detail

If you do something, do it well. Experience shows that tackling a problem at its root usually has a much greater effect than treating the symptoms over and over again. For this reason, there is a focus on pursuing a scientific standard in the work. Consider things such as well-written code, tests that are reliable and valid, and visually attractive reports.


Corporate Social Responsibility (CSR) plays an important role within this organization. The items below are an indication of how Theo runs a future-proof conversion optimization company.

  • Planting trees: For every new customer he plants 10 trees via TreesForAll. Every collaboration starts with a positive impact on the climate, biodiversity, and a healthy living environment. The trees are planted in the Netherlands and abroad.
  • Low consumption: The company is completely paperless and uses green energy. In addition, almost all meetings take place digitally to avoid unnecessary transport. At times when travel is required, this is done by bus and train.
  • Sustainable website: An analysis with Website Carbon Calculator shows that this website produces only 0.08 grams of CO₂ per page view, which is cleaner than 92% of the tested websites. The website also runs on sustainable green hosting.
  • Knowledge sharing: Knowledge is shared about sustainable conversion optimization on our own blog and social media channels. Theo also presents at national and international conferences on topics surrounding sustainability, such as sustainable marketing.
  • Sustainable customers: We are specifically looking for collaborations with more sustainable companies. As a result, well-known green organizations such as Solarfields, Natuurhuisje, Pieter Pot, Greenchoice, and Well Water are among the satisfied clients.
  • Charities: Various charities such as Longfonds and Hartekind have been helped on a voluntary basis with optimizing their websites. The resulting findings have been bundled in an article about CRO for charities.

Besides work

In addition to his work as a freelance conversion specialist, Theo is involved in various matters. He enjoys playing chess or painting landscapes in watercolor. He also likes to get to the bottom of things, for example how to make even healthier green smoothies.

Theo has been with his girlfriend Lisanne for more than 10 years. They share a passion for (among other things) train travel and this has already taken them to beautiful places, such as the Swiss Alps and Swedish Lapland.

Gornergrat train
Conversion optimization specialist
Luzern lake
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Benefits of a conversion specialist

A freelance conversion specialist helps you get to know your visitors and target group better. In addition, he or she will ensure that you can use your online marketing budget more efficiently. The results are higher sales and better customer satisfaction.

A conversion optimization specialist?

Unfortunately, this specialization does not have a fixed name. For example, people talk about 'conversion', but also about 'conversion optimization', which in turn leads to a 'conversion optimization specialist'. Ultimately the goal is: optimize websites.

Outsourcing or support?

You can outsource conversion optimization or just get support with this. An important factor here is whether an experienced internal online marketer is available who understands conversion. It is also important whether the consultancy work will be one-off or continuous.

Hire a conversion specialist

Hiring a good conversion specialist can be challenging. After all, how do you know which specialist will deliver the best results for your company? A tip is to look carefully at references and clients for whom you have already worked. This often gives you a good idea of whether a consultant will be a good match or not.