Freelance Growth Hacker

Spanish / English / Dutch

Hi, I’m Bart Stemkens. I turn strategy into weekly execution — from data to creative. With 10 years of experience, I plug into product teams and founders to move fast, test smart, and learn what actually drives growth.

What I do

I help founders & product teams get a grip on their marketing — by setting direction, creating actionable roadmaps, and executing weekly growth experiments.

I plug into your team 2 to 3 days a week. From there, I run growth experiments — across the stack: from data to creative, from ads to onboarding.

I handle most of the work myself. If something falls outside my scope — and AI can’t help — I bring in one of my trusted specialists.

For who I do it

In 95% of the cases, teams bring me in because:

• They’ve got growth ideas, but no system to test or prioritize them
• They need temporary marketing capacity — someone who can step in and adapt fast
• They’re stuck in tunnel vision and want a fresh perspective to move forward (the system and perspective come included)

In the other 5%, they haven’t found product-market fit yet. I don’t rule those out — but only if there’s urgency, grit, and a clear path to validation.

You’ll probably get value from working with me if:

1. You have something people genuinely want — and can prove it
2. You’re ambitious about becoming the best in your space
3. You have someone who can show up to a weekly check-in
4. You’re open to experiments flopping — as long as we learn fast

Testimonials

“Bart is a multi-skilled professional able to make your business grow. He can handle high levels of complexity, and is pleasant to work with at all times.”

— Rens, CEO @ KIMO

“With Bart, you have everything you need to grow and scale—no extra resources required. If you could clone him, you’d leave your competitors in the dust.”

— Sarah, Head of Growth @ Small Improvements

“Smart, pragmatic, hard-working, and a great guy to have around. Our intake doubled, and costs were cut in half. Bart takes initiative, makes decisions, and gets things done.”

— Marnix, Proposition Manager @ Nationale-Nederlanden

→ view all testimonials

Client cases

Squla (Edtech)

From zero to 5,000 paying users in 14 months — with 90% trial-to-paid conversion.

KIMO (AI learning platform)

150,000 onboarded users in 10 countries, with low CPA and improving D1 retention.

Bieden & Wonen (Proptech)

From 3 to 10 franchise offices, while cutting lead costs by 50%

→ view all cases

Get in contact

If the testimonials or cases weren’t enough to convince you to schedule a call, I’ve got one last move: send me your website and I’ll reply with one growth experiment you could run tomorrow. Free. No pitch. No strings.

Testimonials

Cases