Deterministic calculations first. Interpretation second.

1. Every result comes from code

The free calculators use explicit Python functions with bounded numeric inputs. The same function powers the browser result, tests and paid-report baseline. There is no language model inside the calculation path.

Each page explains its equation, provides a worked example and states material omissions. Percentage and fixed rates stay visible because a marketplace or payment schedule can vary by country, account and contract.

2. Official rates are presets, not hard-coded authority

When a platform publishes an official fee table, we use it to prepare a dated preset. A preset is a starting point. The user can and should reconcile it to an actual account statement before making a material pricing decision.

A weekly monitoring script retrieves selected official source pages, normalizes their text and compares a cryptographic hash with the previous version. A change creates a review alert; it never edits a live fee automatically. Financial rates require human verification before publication.

3. AI is constrained to narrative

An optional Profit Action Report receives the submitted inputs, deterministic output and deterministic one-variable sensitivity tests. It may organize findings and proposed experiments. It is instructed not to invent, recalculate or override a number.

The OpenAI integration uses a structured schema. When the API is disabled or unavailable, a rules-based report is generated so paid delivery does not depend on a third-party model response.

4. Content must earn its own page

We publish a separate URL only when it has a distinct formula or decision context. Currency, country and minor keyword variants belong inside one calculator through presets and editable inputs. This prevents near-duplicate pages and keeps update work concentrated.

5. Corrections and versioning

Every calculator carries a last-reviewed date. Material formula changes require a test update, an explanation in the page source note and a deployment review. Corrections can be reported through the contact address.