Arithmos
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Founding Product Designer
Full-time
Open role
Arithmos
Founding Product Designer
Define the visual + interaction language for retail direct indexing. From OG cards to the prompt-to-portfolio flow.
Location: London (hybrid) or Remote (UK/EU)
Type: Full-time
Salary: £130,000–£160,000 base
Equity: 0.75%–1.25%
Performance bonus
About Arithmos
Arithmos is building the retail layer for direct indexing. We turn a plain-English idea into a transparent, rule-based portfolio with institutional-grade backtesting and analytics. Our goal is to make structured investing accessible to millions.
The Role
You will own the visual + interaction language end-to-end — from the marketing surface and OG cards through the build flow and portfolio analytics. The product is dense, financial, and trust-sensitive; the design has to make all of that legible without dumbing it down.
What You’ll Do
Product Surface
- Prompt-to-portfolio flow: build-card UX, agent live-log, holdings table
- Backtest analytics: charts, lookback rows, attribution factsheets
- Sharing surface: index pages, OG cards, embeddable widgets
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Brand + Marketing
- Homepage, /how-it-works, blog, and pricing visual systems
- Social cover layouts, ad creative, and bio-link page
- Brand guidelines (typography, palette, motion)
Design System
- Tokens for the dark amber/mono terminal aesthetic
- A pattern library other engineers can ship from
Requirements
- 5+ years shipping product design on data-dense web products
- Strong type, layout, and information-hierarchy chops — fintech-grade
- Comfortable working in Figma alongside an IC engineer (no PM intermediary)
- Built a recognisable brand, not just screens
Nice to Have
- Background in fintech / brokerage / portfolio tools
- Charting or data-viz expertise (D3, Highcharts, Recharts)
- Motion / Lottie / Rive experience for marketing surfaces
Why This Role is Exceptional
- Greenfield brand — your typography choices are the brand
- Rare chance to own product and marketing surface together
- Direct reporting line to the founders, no design committee
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Compensation & Benefits
- Base Salary: £130,000–£160,000
- Equity: 0.75%–1.25%
- Performance Bonus
- Private healthcare
- 25 days holiday + bank holidays
- Top-tier equipment + Figma org seat
- Flexible working
- Annual company offsite
How to Apply
Upload your CV and a short note — no more than 200 words — on why this role in particular. If you have work you’re proud of that’s relevant (a product you shipped, a research paper, a backtest you ran), link to it. Two-stage process: screening call, then a take-home + technical deep-dive with the team you’d join.
Applying for Founding Product Designer
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Arithmos is an equal-opportunity employer. Published 7 May 2026.
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