UX/UI

What does UX/UI mean?

UX/UI (user experience and user interface) describes two related areas of the design of digital products. UX covers the whole experience of using a product, that is, whether a user reaches their goal, how much effort that takes and how they rate the use. UI is the visible, operable interface: the layout of screens, controls, typography, colours and the system's feedback. For a ticket machine, the UI would be the arrangement of buttons and display, and the UX the question of whether a traveller is holding the right ticket after one minute.

Part 11 of the DIN EN ISO 9241 series of standards describes usability as the extent to which users achieve their goals effectively, efficiently and satisfactorily. For software companies, UX/UI is therefore not a matter of taste but a cause of measurable metrics: activation of new users, retention, recommendation and support effort. In funding rounds and company sales, design is rarely examined as such but is read off these metrics.

Difference between UX and UI

UX concerns processes and structure: which steps a registration requires, how quickly a new user experiences the core benefit and whether information is where it is looked for. Core benefit means: the user achieves for the first time what they use the product for, for example the first quote sent. The UI translates these processes into concrete screens. An attractive interface does not compensate for a cumbersome process; conversely, an unclear interface can devalue a well-thought-out process.

Many companies work with a design system, a collection of reusable controls and rules. It ensures a consistent appearance and speeds up the development of new features.

Effect on metrics

• Activation: the share of new users who reach the core benefit within a certain period. It depends heavily on the first minutes of use and is the central lever in product-led growth (PLG).
• Retention: users who do not reach their goal often leave without complaint. Good design shows in a higher retention rate (retention rate) across cohorts, that is, across groups of users who started in the same period.
• Recommendation: Satisfied users are more likely to recommend a product, measurable for example through the Net Promoter Score, the share of enthusiastic users less the share of critical users. Recommendations reduce the cost of customer acquisition.
• Support effort: Every enquiry arising from unclear operation causes costs that grow with the number of customers.
• Sales cycle: A product that explains itself in the demonstration shortens the time to closing in business with enterprise customers.

Legal requirements for design

In business with consumers, design is also legally regulated. Under Section 312j of the German Civil Code (Bürgerliches Gesetzbuch, BGB), the button with which an order subject to payment is completed must clearly indicate the obligation to pay, for example with the wording “order with obligation to pay” (German: “zahlungspflichtig bestellen”). Otherwise the contract does not come into being. If consumers can conclude contracts for continuing services on a website, for example a subscription, Section 312k BGB requires a cancellation button. If it is missing, consumers can terminate at any time without observing a notice period.

Manipulative design that pushes users into unwanted decisions (dark patterns) is prohibited for providers of online platforms under Article 25 of the EU Digital Services Act and can also be open to challenge under competition law. Examples are hidden reject buttons or a cancellation that requires considerably more steps than signing up.

Since 28 June 2025, the German Accessibility Strengthening Act (Barrierefreiheitsstärkungsgesetz) obliges providers of certain products and services for consumers, including services in electronic commerce, to design them accessibly. Micro-enterprises that provide services are exempt. Breaches of such requirements can lead to cease-and-desist letters, orders by authorities or ineffective contracts. They are therefore the subject of legal due diligence, that is, the review of the company by investors or buyers before the transaction.

Significance for valuation and integration

Investors assess UX/UI through data: curves of activation and retention per cohort (cohort analysis), conversion of trial users into paying customers and support enquiries per customer. If these values demonstrably improve after product changes, this shows that the team improves its product systematically. Screenshots in the pitch deck, the presentation for investors, do not replace this evidence.

In a company sale, integration is added. If a buyer moves the product into its own interface, the forced changeover can unsettle users and temporarily increase churn. This belongs in integration planning.

Worked example

A software provider wins customers through a free trial phase. It spends EUR 200,000 per month on marketing and receives 2,000 registrations for it. So far, 25% of those registered reach the core benefit within seven days, and 20% of these become paying customers. Each customer brings a monthly gross profit, that is, revenue less direct costs, of EUR 150. A revision of the sign-up flow, in which form fields are removed and sample data is pre-filled, raises activation to 35%.

• New customers so far: 2,000 × 25% × 20% = 100 per month
• Cost per new customer so far: EUR 200,000 divided by 100 = EUR 2,000
• Payback period so far, that is, the time until gross profit has recouped the acquisition cost: EUR 2,000 divided by EUR 150 = about 13.3 months
• New customers after the revision: 2,000 × 35% × 20% = 140 per month
• Cost per new customer now: EUR 200,000 divided by 140 = about EUR 1,429
• Payback period now: EUR 1,429 divided by EUR 150 = about 9.5 months

With an unchanged marketing budget, the cost per new customer falls by just under 29%, and the payback period (CAC payback period) falls below twelve months. For investors, this change is more informative than any description of the design.

Distinction from related terms

• Product management: decides which problems a product solves and which features it gets. UX/UI designs how users experience and operate these features.
• Customer satisfaction (CSAT, Customer Satisfaction Score): measures the rating by customers after an interaction. It is a possible consequence of good design, but not a measure of the design itself.
• Brand identity: a company's logo, colours and tone of voice. The UI adopts elements of these, but is geared to usability rather than recognition.

Common mistakes

• Redesign instead of improvement. A complete overhaul changes many things at once; afterwards it can no longer be determined what worked.
• Decisions by taste. Management's opinion does not replace observing real users on concrete tasks.
• Only the surface revised. New colours and fonts do not improve a process that requires too many steps.
• No measurement. Without recorded activation and retention before and after a change, its effect remains an assertion.
• Legal requirements overlooked. Missing cancellation buttons or unclear order buttons in consumer business endanger contracts and revenue.

Frequently asked questions

Does a young software company need its own designers?

Not necessarily for the interface, but certainly for the processes. Ready-made design systems largely cover the appearance. Whoever is responsible for the processes and regularly tests with users usually has the greater influence on the metrics.

How can UX be measured?

Through task success, time to core benefit, activation rate and support enquiries per hundred users. Surveys complement these values but do not replace them.

How many users does a meaningful test need?

That depends on the purpose. To identify the biggest hurdles, a rule of thumb is that a small group of about five users, observed on concrete tasks, is enough. For reliable statements about metrics, however, comparison tests (A/B tests) are needed, in which two variants are measured at the same time on separate, considerably larger groups of users.

Do buyers examine the design of a product?

Rarely directly. Buyers examine usage data, cohorts and customer satisfaction and in part talk to customers. In consumer business, they additionally check whether the legal requirements for ordering and cancellation processes are met.

The Roemer Capital view

In a funding round, we prepare a client's product quality through metrics, not screenshots: activation rate, retention per cohort and customer acquisition cost before and after significant product changes. These series belong in the financial model and the data room.

The results are mirrored against two benchmarks: a ratio of customer lifetime value to acquisition costs (LTV/CAC) of at least 3 to 1 and a payback period of acquisition costs under twelve months. Better user guidance is often the fastest way to reach both values without increasing the marketing budget.