Ellie Sleightholm
Technical and Mathematics Reviewer
Every calculator on this site is a piece of software making financial calculations, and software deserves independent review.
Ellie Sleightholm reviews the mathematics behind our calculators: the formulas, the calculation engines, the boundary cases, and the automated test suites that prove each tool does what its page says it does.
Background
About Ellie
- Master's in applied mathematics, University of Cambridge
- Part III
- Mathematics degree, University of Leeds, with the King Prize
- First
- Combined audience for her mathematics content
- 250,000+
Ellie is a mathematician and software engineer. She holds a master's degree in applied mathematics (Part III) from the University of Cambridge and a first-class mathematics degree from the University of Leeds, where she was awarded the King Prize for finishing top of her year in applied mathematics.
Today Ellie is one of the UK's best-known mathematics communicators. She is a mathematics and physics writer and director at Veritasium, one of the world's largest science channels, and her own mathematics content on YouTube, Instagram, and TikTok reaches a combined audience of more than 250,000 people.
She has worked with the UK Space Agency, the Royal Society of Chemistry, and the Department for Education on national STEM campaigns, appeared on BBC Breakfast, and is a prominent advocate for women in STEM.
Space industry
Lead astrodynamics software engineer, SmallSpark Space Systems
Her engineering career began in an environment where a calculation error has real consequences.
Two years
Machine learning engineer and head of developer relations, Marqo
An AI search company.
Today
Mathematics and physics writer and director, Veritasium
One of the world's largest science channels.
Scope
What Ellie Reviews on This Site
Ellie's review covers the computational layer of every calculator: that the implemented formulas match the stated rules, that band boundaries, tapers and reducing balances behave correctly at their edges, that date arithmetic is right, and that the automated test suites genuinely exercise the logic they claim to. Each calculator on this site ships with its engine tested against worked examples before publication.
| Calculator | What the review covers |
|---|---|
| Benefit in Kind Calculator | CO₂ banding logic, multi-year rate projection, marginal rate calculations |
| HMRC Maternity Calculator | Date arithmetic for qualifying weeks and leave windows, phase switching, rate boundary handling |
| Sole Trader vs Limited Company Calculator | Parallel tax computations, marginal relief formula, dividend band stacking, crossover chart |
| Capital Allowance Calculator | Relief routing logic, reducing balance schedules, allowance date boundaries |
| HMRC Penalty Calculator | Penalty ladder boundaries, piecewise historic interest calculation, multi-year stacking |
Boundaries
What Ellie Does Not Do
Those figures are verified separately against primary sources such as GOV.UK and HMRC publications, and every calculator lists its rates, sources, and assumptions in a panel you can check yourself. The division of labour is deliberate: official sources for the rules, an independent mathematician for the machinery, and our Disclaimer for what the results can and cannot tell you.
Elsewhere