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Senior/Lead Machine Learning Engineer (Predictions)

London

400M+ downloads. 75M+ monthly users. A decade of building – and we’re still accelerating.

Flo is the world’s #1 health app 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 6M 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.

The job

We are Flo, the world’s most popular female health app! Our engineers aren’t just building a better product; they’re making the world a better place by improving female health. We leverage Machine Learning and AI to create a more personalised experience for our users, from providing more accurate cycle predictions to delivering relevant, personalised, and medically credible health insights. 

We are looking for a Machine Learning Engineer to join the Predictions team. This team focuses on one of the cornerstone features of the Flo Health app: delivering accurate predictions to our users about their cycles and more. We develop state of the art solutions to provide the most accurate predictions to our users on the app. To do so, we leverage a range of different data points and machine learning techniques to ensure the best user experience. This role will focus on our menstrual cycle modelling, finding patterns and regularities in symptoms, symptom predictions, utilising data from wearable devices, and more. If you’re passionate about technology and driven by delivering value to users, we would love to hear from you!

Your Experience

Must have:

  • Solid understanding of classical ML algorithms
  • Demonstrated success in building and deploying large-scale machine learning models that serve users in real-time
  • Ability to devise creative solutions to intricate technical challenges, including experience in systems design with the ability to architect and explain ML pipelines
  • Strong Python programming skills for efficient model development and deployment
  • Experience in building and managing data pipelines using tools like Apache Spark
  • Familiarity with different feature engineering techniques
  • Excellent communication skills and ability to collaborate with diverse teams
  • Commitment to responsible AI practices, including fairness, accountability, and transparency

Nice to have:

  • Advanced degree in Computer Science, Mathematics, or a related field
  • Familiarity with statistical and measurement fundamentals (including time series analysis), and running and evaluating AB tests
  • Strong data visualisation skills to help narrate stories from data
  • Experience in the MedTech domain

What you'll be doing

You'll be responsible for:

  • Explore, develop and test complex ML systems to improve female health by delivering more accurate and personalised insights to the users
  • Work in a fast-paced environment, to quickly build and validate product hypotheses, taking end to end ownership of the ML products
  • Constantly improve our technical capabilities by researching and implementing state of the art ML solutions that deliver value to users
  • Work in a cross-functional setup alongside other engineering (ML, Backend, Frontend, QA), product, and analytics teams

#LI-Hybrid #LI-LM12

Salary Range - per year

£80,000 - £150,000 GBP

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

We support impact with meaningful reward. Here’s what that looks like:

  • 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
  • Flexible office + home working, up to 2 months a year working abroad
  • 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. Read our privacy notice for job applicants.

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