About
Why we built this
The internet runs on thousands of small tools that millions of people rely on every day. Many are poorly maintained or full of ads, but people use them because they have to. Casomo exists because of that gap — instead of building ever larger systems, we build focused tools that solve specific problems and stand on their own.
NHS financial tools came first because we hit the problem ourselves. Working out what an NHS pension is worth — and how it changes under different scenarios — turned out to be genuinely difficult. The information is spread across multiple documents. The assumptions behind most online calculators aren't shown, so you can't tell whether the answer applies to your situation. We started building the tools we wanted to use ourselves.
How we work
Every calculation is tested against real NHS payslips before it ships. We run the same inputs through our engine and compare line by line. If the numbers don't match, we find out why before anything goes live.
The tax and pension logic lives in a public library, separate from the website. Anyone can read the source code, file an issue or check a specific rule. Keeping it open means errors get found faster and trust doesn't depend on taking our word for it.
When HMRC publishes new tax rates or NHS Employers issues a pay circular, we update the library the same week. Every rate in the system carries a date and a source link back to the official document. If a number changes, the previous value stays in the version history so you can see exactly what moved and when.
Who we are
David Mohamad
Founder
I founded Casomo. My background spans physics R&D, medical robotics, defence systems, and fintech — the common thread is building software where getting it wrong has real costs. I now apply the same rigour to tools ordinary people use every day.
Hannah Paten
Contributor
I lead communications and stakeholder engagement at a major NHS trust, spanning healthcare, academia, and the wider public sector. My work focuses on shaping strategic messaging and building relationships with key stakeholders to support organisational priorities.
Our promise
No ads, no data sales, no affiliate commission. We use one privacy-first analytics tool (PostHog), proxied through our own domain, with all inputs masked and no advertising pixels. We watch how the tools are used so we can find what is broken, make them work well, and build more relevant content. People rarely email to report a bug — they just leave. The data is anonymous, and we never sell it to third parties. If we can't verify a number, we don't publish it. If we get one wrong, we fix it and say so.
Contact
Spotted a mistake? Want a tool we haven't built? Disagree with how we've modelled something?
Email us