Flutter Development & Compliance-First Architecture

A Tax Engine Reconciled to a Licensed Accountant's Own Numbers

BPC

Sri Lanka — included as architecture evidence, not an EU engagement

Knovik built a Flutter app for BPC, a licensed accounting firm, whose on-device tax engine computes personal income tax entirely offline — reconciled line-by-line to BPC's own computation template rather than a generic simplification — with a consent-gated handoff to a licensed accountant for anything the engine flags as uncertain rather than guesses at.

Overview

BPC needed a way for taxpayers to work out their personal income tax without exposing sensitive financial and identity data to a server by default, while giving BPC's own accountants a clean, consent-gated path to review and file. The relevant pattern for an EU compliance buyer: the free tier's entire calculation runs on-device with zero network calls, and any category the engine can't confidently compute is explicitly flagged for human review rather than silently guessed at — the same 'flag it, don't guess it' discipline that matters for GDPR-adjacent automated-decision concerns.

Approach

Reconciled to a Real Spreadsheet, Not a Generic Calculator

The firm's own computation template became the engine's test case: every threshold and relief was implemented to reproduce that spreadsheet's cached results exactly, not a simplified textbook version of the tax code.

Consent-Gated Handoff, Not Silent Data Collection

The free tier never makes a network call to complete a filing — all data lives on-device. The paid tier only transmits a filing after an explicit, per-filing consent action, to a backend enforcing an automatic, scheduled purge policy.

Flag It, Don't Guess It

Categories the engine can't confidently compute are deliberately excluded and routed to a human reviewer instead of silently miscalculated — the discipline that matters most when an automated system's output has real financial consequences.

Technologies

FlutterDartDrift (SQLite)RiverpodSupabase (Auth only — no tax data stored)

Verified Results

As of 24 July 2026

  • Engine output matched the firm's own worked example to the cent
    Every intermediate figure asserted against a real benchmark, not just the final number.
  • Zero tax data in third-party auth storage
    The identity provider holds only login credentials — no filing or profile data — confirmed by inspecting what the backend actually stores.

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