Senior / Lead iOS Engineer in London

500M+ downloads. 80M+ monthly users. A decade of building – and we’re still accelerating. Flo is the world’s #1 health & fitness app worldwide on a mission to build a better future for female health. Backed by a $200M investment led by General Atlantic, we became the first product of our kind to reach a $1B valuation in 2024 – and we’re not slowing down. With 7M paid subscribers and the highest-rated experience in the App Store’s health category, we’ve spent 10 years earning trust at scale. Now, we’re building the next generation of digital health – AI-powered, privacy-first, clinically backed – to help our users know their body better.

As an iOS Engineer at Flo, you'll help shape the mobile experience for millions of people, and do genuinely meaningful work in women's health. Our app is trusted by 1 in 4 women aged 18–44 in the US and used across 100+ countries, with machine learning and AI powering accurate cycle predictions and personalised, medically credible health insights. We build large-scale mobile applications with rich, intuitive interfaces - optimised for speed, accessibility and privacy. You'll join a cross-functional team working across the full mobile lifecycle, from feature ideation through to release and iteration, with real ownership over value delivery end to end. We're not a feature factory. Our engineers are pragmatic problem-solvers who thrive in fast-moving environments and care about what they ship. You'll have genuine scope to experiment, lead ambitious product initiatives and implement solutions that matter - not just clear a backlog. Flo is a constantly evolving product, and we give our engineers the trust and autonomy to evolve it.

Your Experience

• Must have: 6+ years in software engineering, with at least 3 years focused on building, shipping, and maintaining production mobile applications.
• Expert-level iOS development skills, with a proven track record of delivering high-quality apps at scale.
• Hands-on experience building complex mobile applications with rich, performant UIs — experience in global consumer-facing products is a strong plus.
• Deep proficiency in Swift; working knowledge of Objective-C and solid object-oriented design principles.
• Strong familiarity with Apple's ecosystem — frameworks, HIG guidelines, and end-to-end App Store submission and maintenance processes.
• Clear understanding of the mobile product lifecycle and comfortable working within Agile teams.
• A collaborative, growth-oriented mindset with the drive to take ownership and deliver.

• Nice to have: Solid understanding of UX and interaction design principles, with the ability to collaborate effectively with designers and advocate for quality user experiences.
• Proven experience optimizing mobile app performance over constrained networks, including building and maintaining offline-first architectures.
• Hands-on experience with mobile CI/CD pipelines, including build automation, automated testing, and release workflows.
• Experience integrating with BI and analytics platforms, with familiarity in designing and interpreting A/B tests to drive product decisions.

What you'll be doing

• Building and maintaining features using modern frameworks, libraries, and internal component systems, ensuring consistency, scalability, and code quality across the codebase.
• Delivering polished, engaging user experiences that balance visual appeal with intuitive interaction design.
• Owning and contributing to a robust Continuous Delivery pipeline, ensuring fast, reliable, and safe releases to production.

How we work

We’re a mission-led, product-driven team. We move fast, stay focused and take ownership – from brief to build to impact. Debate is encouraged. Decisions are shared. We care about craft, ship with purpose, and always raise the bar. You’ll be working with people who take their work seriously, not themselves. It takes commitment, resilience, and the drive to keep going when things get tough. Because better health outcomes are worth it.

What you'll get

• Competitive salary and annual reviews
• Opportunity to participate in Flo’s performance incentive scheme
• Paid holiday, sick leave, and female health leave
• Enhanced parental leave and pay for maternity, paternity, same-sex and adoptive parents
• Accelerated professional growth through world-changing work and learning support
• In-person collaboration and work in a hybrid model, with 3 days per week spent in the office
• 5-week fully paid sabbatical at 5-year Floversary
• Flo Premium for friends & family, plus more health, pension and wellbeing perks

Diversity, equity and inclusion

Our strength is in our differences. At Flo, hiring is based on merit, skill and what you bring to the role – nothing else. We’re proud to be an equal opportunity employer, and we welcome applicants from all backgrounds, communities and identities.