Shadow Tax: independent recalculation of customer capital-gains statements
A second, independent calculation of UK capital gains (share pooling, same-day and 30-day matching rules) that compares the result to a platform's customer tax reports before they go out.
Early
Written for: Small startup team
Why now
Wise is negotiating with HMRC to pay tax bills after its software miscalculated gains for about 4,000 users. Every UK investing app now has evidence that tax-report errors cost real money and damage their reputation.
What became possible
Coding agents make it practical to encode HMRC matching rules as a tested rules engine quickly. LLMs can then explain each difference to operations staff in plain language. The domain knowledge, not the AI, is what makes this defensible.
Two ways in
- Pre-release tax report diff
Takes trade and corporate-action data plus the platform's draft statements, recalculates independently, and flags customers whose figures differ, with the cause explained.
- Customer
- Head of Tax Operations at a UK investing app or neobank with an investment product
- Model
- Charge per customer account each tax year, plus an implementation fee
- Remediation calculator
Calculates how much each affected customer needs after an incident has been found, for submitting to HMRC.
- Customer
- Fintechs already in remediation
- Model
- Fee per project
Competition
No product found that sells an independent second calculation to UK investing apps or neobanks to compare against their draft customer CGT statements before release, or a remediation calculator for CGT reporting incidents. Existing vendors (CGiX, FA, Praemium, M&G Cobalt) produce the figures, and Kaizen does independent accuracy testing only for regulatory trade reporting, not tax.
Full competition notes (8 competitors)
No product found that sells an independent second calculation to UK investing apps or neobanks to compare against their draft customer CGT statements before release, or a remediation calculator for CGT reporting incidents. Existing vendors (CGiX, FA, Praemium, M&G Cobalt) produce the figures, and Kaizen does independent accuracy testing only for regulatory trade reporting, not tax. Openings: (1) a check run in the weeks before statements go out that explains why each customer's figures differ, focused on known failure points (account transfers between platforms, corporate actions, equalisation and notional distributions); the lang cat found 1 in 6 advisers aren't confident platforms show their clients' CGT correctly; (2) remediation tooling, where the only example found is Australian (ASIC/Macquarie). Risks: fewer buyers than expected, since some UK apps (e.g. Freetrade, per a possibly outdated thread) don't issue CGT statements at all; customers file their own CGT and platforms rely on disclaimers, so urgency is weak until there's an incident or Consumer Duty pressure; the remediation product's 'submitting to HMRC' output needs defining (corrected figures for customers' own returns vs. redress the platform owes); established engine vendors or Kaizen could add this; big-4 consulting likely already does remediation work (not verified).
- CGiX (Financial Software Ltd)
Described on a paraplanner forum as the institutional market leader in UK CGT engines, behind several platforms' CGT tools; also integrated into SunGard APSYS (https://www.globalcustodian.com/?p=42941). Platforms use it to produce figures, not to check them independently. Most coverage is dated, so check it's still sold.
- FA Solutions – FA Operations
Wealth-platform software that now calculates CGT per customer, with fuller tax reporting planned. Could add a verification mode.
- M&G Wealth 'Cobalt' CGT microservice
A platform's in-house CGT engine covering funds, ETFs and equities. Shows large platforms build or buy the main engine themselves.
- Praemium
Supplied an outsourced CGT calculation service to Cofunds (2008). Historical; current status unknown.
- Kaizen Reporting (ReportShield)
The closest analogy: independent accuracy testing and reconciliation of regulatory trade reports to the regulator (MiFIR). Same 'shadow check' model but for regulatory reporting, not tax. Could expand into tax.
- cgt-calc (open source)
Open-source Python UK CGT calculator applying same-day, 30-day and Section 104 rules to broker exports. Consumer-focused; usable as a reference engine.
- ibkr-cgt (open source)
Command-line tool for Interactive Brokers statements applying UK matching rules, including options and foreign-currency trades. Consumer-focused.
- cgtcalc / timetotrade / Tax-Wizard / Recap
Consumer recalculation tools (Tax-Wizard: https://tax-wizard.eu/en, Recap: https://recap.io/index.md). Individual investors already independently recalculate platform figures; none sell to platforms.
Risks
- Corporate-action data quality is the hard part, not the tax rules
- Market is narrow at first (UK only). Other countries need new rules engines
- Platforms may treat it as a one-off purchase after an incident, not a subscription
Strong team fit; market pull is the weak point (6).
tech 8 · pull 6 · space 7 · fit 9 · build 7
Exposed
Companies that could benefit or be threatened. News and context, not investment advice.
Momentum of its main topic
Sources
What happened next
- +7d · 15 Oct 2026 nothing yet. No product launch, funding, acquisition, or press coverage was found for an independent capital gains tax verification or remediation service in the UK fintech space between October 8 and October 15, 2026.
Status history
- 2026-10-08 Flagged as buildable