Consumer credit
Lending and calculation logic under regulatory challenge
Interest miscalculated across a large customer base, with no record of why the logic had been set up the way it was.
Illustrative · anonymised and reconstructed from real work
The scenario
Where the decision had to hold under scrutiny
Interest on buy-now-pay-later balances had been calculated incorrectly over time, affecting large numbers of customers and creating regulatory risk. The lack of clear validation and oversight allowed errors to persist unnoticed, and there was no record of why the logic had been set up as it was. Illustrative work undertakes a full review of calculation logic and introduces controls to test, monitor, and evidence outputs. This supports remediation and helps ensure the logic is accurate, controlled, and able to withstand scrutiny.
What the scenario turns up
The issues
Finding 01
Interest was being calculated incorrectly across large numbers of customers, and with no validation or monitoring in place, errors of this kind can persist unnoticed.
Finding 02
There was no record of why the calculation logic had been configured as it was, making it impossible to justify to the regulator or to scope redress fairly.
What the work does about each one
The response
Response 01
Runs a full review of the calculation logic and introduces controls to test, monitor, and evidence outputs, so divergence is caught early and correct figures can be shown for remediation and redress.
Response 02
Reconstructs and documents the intended logic and its basis, giving remediation and customer redress an evidenced foundation.
How the work is done
The same five steps, applied to this decision
Every piece of work runs the same path. For this one, the weight falls on Design, Build, Assure & hand over — the steps where a decision of this kind is most often challenged.
Discovery
Map where the decision is made, who could challenge it, and the regime that binds it — before any logic is written.
Design
Set the logic out in the open so it can be read and questioned: the same inputs always give the same decision, and nothing is a black box.
Build
Build it with the checks in: coverage and oversight are confirmed before anything ships, and nothing unassessed is waved through as safe.
Deploy & test
Run it against real cases behind a human checkpoint, and keep a dated record of exactly what was decided and on what basis — one that cannot be edited afterwards.
Assure & hand over
Hand over the decision log and a plain-language write-up, so your team owns the record the moment someone says prove it.
What carries across
No automation covers this case yet
58 automations are running today, each built for a rule it names. None of them covers this case, and that is all that is claimed here. What carries across is the method: every one of them refuses to write a sentence its evidence will not support, which is the discipline this kind of work once ran by hand. Any of them can be shown to you running.
Related cases
The same standard, holding elsewhere
Discuss your situation
A decision like this can be made correctly, and shown to be correct, on the record
A short discussion is usually enough to locate where the risk sits — in the logic, the controls, the evidence, or a combination — and where it is made to hold.