UX/UI CASE

Small hints, big results: how a redesigned postal code input increased revenue by 14%

A UX/UI case study on designing for user reality instead of system requirements.

Iteration evolution of the postal code modal design.

UX/UI CASE

Small hints, big results: how a redesigned postal code input increased revenue by 14%

A UX/UI case study on designing for user reality instead of system requirements.

Iteration evolution of the postal code modal design.

THE CHALLENGE

When simple forms create complex problems

Dutch postal codes are unique: 4 numbers + 2 letters.

Seems simple, right?

Yet on Schildervergelijker.nl, where we connect people with painting professionals, our data showed a troubling pattern: a huge number of users were getting stuck at the very first step – entering their postal code.

The business impact was threefold:

  • Users got frustrated with unhelpful error messages and abandoned the site
  • Painters missed out on potential jobs in their area
  • Our business lost valuable conversion opportunities

THE INVESTIGATION

What do users actually need to succeed?

Digging into Google Analytics revealed that many users tried multiple times to enter their postal code, often abandoning entirely after repeated errors. Hotjar recordings confirmed the pattern – users were:

  • Entering only the numeric portion (1234)
  • Adding spaces between numbers and letters (1234 AB)
  • Clicking the “Enter” button without inputing a value


The core problem? Although our system expected a “1234AB” format, there was no visual guidance or instructions to convey that.

Furthermore, eventual feedback offered only a generic error message: “Your postal code doesn’t seem to be correct.”

Old postal code input field

THE SOLUTION

Show, don't just tell

Rather than expect users to guess the correct format, I designed a more intuitive input experience:

  • Visual placeholder showing exactly 6 characters (4 numbers + 2 letters)
  • Clear example text “1234AB” as a reference
  • Real-time validation with color feedback (green for correct, red for errors)
  • Contextual error messages explaining specifically what went wrong
  • Smart keyboard switching on mobile (numbers → letters automatically)


The first iteration maintained the same overall design structure of the interaction modal, while giving users the guidance they needed before hitting submit.

Redesigned postal code input field

THE EXPERIMENT

Testing against real user behavior

We A/B tested the redesigned input field with over 24,000 users over 56 days. The results were clear:

  • Invalid postal code errors dropped by 31.8%
  • More users successfully entered the form flow (+3.2%)
  • Conversion rate increased by 11.2%
  • Monthly revenue increased by +14.2%

-31.8%

Decrease in postal code errors

+3.2%

Increase in form flow entrance

+11.2%

Conversion rate increase

+14.2%

Monthly Revenue Increase

THE ITERATION

Building on success

Initial success gave us the confidence to push further.
Our next challenge: could we improve the landing page experience while maintaining the benefits of the improved postal code input?

We redesigned the entire input modal, making it more compact and visually appealing. This smaller footprint accomplished two crucial things:

  • Created space to showcase more of the background imagery (crucial for service businesses)
  • Established better visual hierarchy between the page title, supporting copy, and the input area


The results across multiple websites confirmed our approach. Even on sites where fewer users initially entered the form, we saw significant increases in consumer requests and revenue. 

Each iteration taught us something new about the relationship between form design and user behavior.

The most interesting discovery?
Even when the design change seemed minor to us, the impact on user behavior and business outcomes was substantial.

Modal evolution: with every iteration a new learning. The final design had better hierarchy and a minimalist modal, which allowed for a better view of the background image, specially in mobile devices.

THE OUTCOME

Success worth replicating

The success of these iterations led us to test the same approach across multiple other websites in our portfolio, including concepts in Belgium, France, Italy and Spain.

Even though the postal code formats on these countries were simpler (only numbers), the pattern held true – all sites showed revenue increases and error reductions.

Eventually, the improved redesign was rolled out to all 30+ service websites of the company.

THE TAKEAWAY

Design for how users actually behave, not how systems expect them to

Often, the most impactful UX improvements aren’t radical redesigns but thoughtful refinements that bridge the gap between system requirements and user behavior.

By focusing on the point where users were struggling most – the very first interaction – we were able to create a smoother path through the entire service. Users who start with a successful experience are more likely to complete their journey.

The best part? This solution required no backend changes or complex technology – just careful observation and thoughtful design.