Case study 1/4
From free tool to paid SaaS.
I redesigned a beloved free engineering tool into a paid SaaS product — without losing the community that made it valuable.
- My Role
- Lead UX/UI Designer / Product Strategy Advisor
Context
KalkulatorPro.pl is a free suite of engineering calculators that built a loyal community through word of mouth alone.
The challenge wasn't building a paywall — it was converting a trusted free tool into paid SaaS without breaking that trust.
- 3,000+
- Engineers
- 40+
- Calculators
- 99.9%
- Uptime
- PN/EN/DIN
- Standards compliant
Solution
Signup only asks for email and password — '5 days free, no card required,' with billing deferred to the end of the trial.
A real phone number stays in the footer — a low-cost fallback for less digitally fluent users, still handled personally by the owner.
Problem — "Floating Form"
A small calculator form sat in the top-left corner above a large, empty white area. No instructions, no explanations, no supporting content. The page visually signaled "unfinished," making it hard to justify a paid subscription.
Solution — "Content Stack"
Every calculator page was rebuilt around a full content stack — a 3-step usage guide, recommended engineering values, formulas, comparison tables, and FAQ — wrapped around the calculator form.
Design Tokens Systematization
The visual system was rebuilt on Tokens Studio — semantic tokens for color, typography, spacing, radius, and shadow — replacing ad hoc, page-by-page styling across 40+ calculator pages. This keeps the product consistent as it scales and bakes WCAG contrast requirements into the system by default.
Results
Paid subscribers grew from ~100 to ~190 after launch — a coordinated release, so no single change can be isolated as the cause.
The dedicated B2B section now drives ~10 inbound inquiries a month — a channel that didn't exist before.
100 → ~190 (+90%)
Paid subscribers following the redesign launch
~10 leads / month
Inbound B2B inquiries via the dedicated "For Teams & Companies" section
Design Review Q&A
That's a real trade-off, made deliberately. A card-at-signup filters for purchase intent, but it also filters out exactly the audience this product needed most: existing free users who'd never paid and needed to re-experience the tool's value first. With usage data in hand, I'd want to see trial-to-paid conversion split by acquisition source before calling it settled.
Keeping the core interaction unchanged kept the perceived "betrayal" surface small. Once the paywall went live, students and university staff — never the monetization target — started dropping off as a side effect. That wasn't predicted upfront; the free-access path for that segment was a reactive fix, not a planned mitigation. I don't have churn data to prove this worked — only the owner's qualitative read that signups stayed steady and annual sales were strong.
I'm not claiming a measured lift — I don't have that data. What I can defend is the diagnosis: the "floating form" signaled unfinished quality right at the moment a user decides whether to pay, and content-rich pages are a well-documented pattern for building authority in exactly that moment.
Forty-plus pages built up ad hoc over years is exactly where design debt compounds fastest — and the product wasn't staying at 40 pages, it was adding account screens, pricing tiers, and billing. Skipping a token layer just means every new surface duplicates inconsistent styling or needs a redesign pass later, at higher cost than the token system upfront.
