When I started building iatroX Calculators, the question was not "can we build clinical calculators?" — anyone can implement a scoring formula. The question was "can we build calculators that are genuinely more useful in UK clinical practice than what already exists, and can we do it in a way that scales to every score a working doctor might need?"
The answer required solving four problems that existing calculator platforms either ignore or solve poorly: clinical context (UK guidelines, not US), discoverability (finding the right tool in seconds, not minutes), interpretation (what the score means clinically, not just numerically), and workflow continuity (connecting one score to the next in a clinical pathway).
This article explains what we built, how it works, and the clinical thinking behind the design decisions.
The Architecture: Schema-Driven Calculators With Editorial Content
Every calculator on iatroX is defined by a structured schema that separates the calculation logic from the clinical content. This is a deliberate architectural choice — it means we can add new calculators rapidly (the schema handles rendering, input validation, and unit conversion automatically) while investing editorial time where it matters most: the clinical interpretation, the safety caveats, and the guideline references.
Each calculator schema includes the calculation engine (the formula, scoring rules, or decision logic), input definitions (variable names, types, ranges, units, and validation rules), result interpretation bands (with colour coding, clinical guidance text, and next-step recommendations), clinical pearls (the practical insights that source literature alone does not convey), safety caveats (when the tool should not be used and what to consider instead), source references (original validation studies with PubMed links), and related calculator links (the next tool in the clinical workflow).
The universal renderer takes any schema and produces a consistent, mobile-optimised calculator interface — the same interaction pattern whether you are using QRISK3 (which requires 15+ input variables) or Glasgow Coma Scale (which requires 3). This consistency matters for clinical usability: once you have used one iatroX calculator, you know how to use all 80+.
Five Calculator Types
Not all clinical calculators work the same way. We defined five tool types, each with its own rendering logic:
Score calculators sum weighted criteria to produce a risk score (CHA₂DS₂-VASc, Wells PE, CURB-65, Caprini). The result is a number with defined interpretation bands.
Formula calculators apply a mathematical formula to continuous variables (CKD-EPI eGFR, Cockcroft-Gault, corrected calcium, BMI). The result is a calculated value with clinical reference ranges.
Questionnaire calculators present a standardised patient-reported outcome measure (PHQ-9, GAD-7, AUDIT-C, Edinburgh PND Scale). The result is a severity score with treatment thresholds.
Decision rule calculators apply a binary or stepwise algorithm to determine a clinical action (PERC Rule, Ottawa Ankle Rules, Canadian C-Spine Rule). The result is a recommendation: image/do not image, admit/discharge.
Staging calculators classify disease severity into defined stages (Child-Pugh, KDIGO CKD staging, KDIGO AKI staging, TNM). The result is a stage with prognostic and management implications.
Each type has specific rendering optimisations. Questionnaire calculators present items sequentially with response options. Decision rule calculators present criteria as a checklist with early termination (if the first PERC criterion is positive, the rule cannot be applied — the calculator tells you immediately rather than making you complete all 8 criteria). Staging calculators present the staging criteria and the clinical implications of each stage side by side.
Semantic Search: Clinical Concepts, Not Calculator Names
The search bar at iatrox.com/calculators is the single most important UX decision in the product. It uses semantic matching across calculator names, clinical concepts, synonyms, associated conditions, and common shorthand.
This means you can type "liver fibrosis" and get FIB-4, NAFLD Fibrosis Score, and Child-Pugh — even though none of those calculator names contain the words "liver fibrosis." You can type "GI bleed" and get Glasgow-Blatchford and Rockall. You can type "suicide" and get C-SSRS and PHQ-9. You can type "anticoagulation" and get CHA₂DS₂-VASc and HAS-BLED.
The search indexes calculator titles, associated clinical conditions, clinical domains, common abbreviations, and the clinical scenarios where each tool is used. The result is that the search works the way clinicians think — by clinical problem, not by memorised score names.
The Unit Conversion Safety Layer
Drug dosing calculators and formula-based tools require numerical inputs with specific units. A creatinine value of 1.2 could be 1.2 mg/dL (US convention) or 1.2 µmol/L (UK convention) — and using the wrong unit in a Cockcroft-Gault calculation produces a dangerously wrong result.
Every numerical input on iatroX Calculators has a defined unit with clear labelling. Where multiple unit systems exist (creatinine in mg/dL vs µmol/L, weight in kg vs lb, height in cm vs feet/inches), the calculator defaults to UK conventions and provides unit conversion where clinically relevant. This is a safety feature, not a convenience feature — unit errors in clinical calculations cause real patient harm.
Editorial Quality: Every Calculator Reviewed Against Source Literature
Every calculator on iatroX was built from the original validation study — not copied from another calculator site. The scoring criteria, the interpretation bands, and the clinical thresholds are verified against the primary PubMed-referenced source. Where subsequent validation studies have modified the interpretation (as with the age-adjusted D-dimer threshold, which post-dates the original Wells validation), the most current evidence is used and cited.
The clinical pearls and safety caveats are written from clinical experience — the practical knowledge that source literature alone does not convey. The Wells PE pearl about the subjectivity of "alternative diagnosis less likely." The NEWS2 pearl about Scale 2 misuse in COPD. The PHQ-9 pearl about item 9 requiring a specific safety response. These are the insights that make a calculator clinically useful rather than just mathematically correct.
Why This Matters for Clinical Practice
Clinical calculators are decision support tools — they exist to make clinical decisions more accurate, more consistent, and more defensible. But a calculator that gives you a number without telling you what it means in your clinical context is only doing half the job. A calculator that defaults to the wrong jurisdiction's guidelines is actively misleading.
iatroX Calculators is built to do the whole job: accurate calculation, UK-guideline-referenced interpretation, practical clinical pearls, safety caveats, and workflow continuity to the next tool. 80+ tools. One search bar. No ads. Free.
Built by a solo NHS GP founder who uses these tools in practice every day — because the best clinical tools are the ones built by the clinicians who need them.
Available at iatrox.com/calculators.