How we check the numbers

A projection is only useful if the arithmetic behind it is right. This page explains how the maths is tested, where the figures come from, when they were last checked and what the checks do not cover. It describes what is in place today. It is not a promise that every figure is correct for your situation.

Automated tests

The calculation engine is a single piece of code that turns a plan into a month-by-month projection. It is tested in four ways.

• Independent law tables. Income tax rates, study loan repayments and stamp duty scales are typed again, separately from the engine, in the form the ATO and state revenue offices publish them. The engine must match them across a dense grid of incomes and prices. If a rate is changed in one place and not the other, the test fails.
• Random households. Hundreds of made-up households are generated, from singles to couples, with salaries, bonuses, study loans, homes, investment properties, shares, debt recycling, cash, loans, salary sacrifice and retirement. Each is projected, and every month must satisfy accounting rules. For example, cash must reconcile and tax must never fall as income rises. When a rule breaks, the test prints the smallest plan that breaks it.
• Hand-worked cases. Small, clean households where the answer can be found with a calculator, such as a growth rate that must produce exactly that growth over twelve months. Each test states its formula.
• Guide figures. The dollar figures in every published guide are recomputed by tests and looked for in the text. If a rate changes and a guide is not updated, the check fails. One video episode is checked the same way. The household counts quoted on this page are checked against the audit too. The estimates shown next to each opportunity are also tested for sensible size and wording.

The engine also has fixed reference results, known as golden tests, for tax, stamp duty, super, loan balances and debt recycling. They were generated from published rates by a script rather than copied from an outside spreadsheet. They stop the results changing without anyone noticing, but they are only as good as the rates they were built from, and some are due to be regenerated after the 2026 rate changes.

When the tests run

• The standard checks run on every change pushed to the main branch and on every pull request. They cover type checking, code rules, all tests and a full build, including the audit above with 150 random households.
• A deeper run with 1,500 random households starts every Sunday, on any pull request that changes the engine, a guide or a video, and by hand. It takes a few minutes.

Where the figures come from

Market assumptions, such as investment returns, inflation and savings interest, are not law. They are editable defaults and are labelled as assumptions wherever they appear. Law and published figures are re-checked each 1 July and when we learn of a change. The dates in the table show when each was last checked.

What the checks cannot tell you

• The tests check the code against our reading of the rules. They cannot show that a rule has been read correctly, or that it applies to your circumstances.
• Tax is approximated by month. Tax is withheld each month and reconciled on 1 July each year, so the timing of refunds and bills is an approximation of how your actual return works.
• Rounding. Money is held in whole cents, and rates are applied as effective annual rates. Small differences from a lender, fund or the ATO are normal.
• Steady returns. Growth, inflation and interest are constant yearly assumptions. Markets do not behave that way, and the model does not simulate them.
• Left out. The Age Pension and other Centrelink payments, aged care, transition-to-retirement pensions and death benefit tax are not modelled. Services Australia figures are therefore not used in the projection.
• Law that is changing. Changes to negative gearing and the capital gains tax discount start on 1 July 2027. The engine applies today's rules by default, and does not yet apply the indexation and minimum tax that replace the discount.
• Known gaps. A few stamp duty items are still marked for follow-up, including part of the New South Wales first home concession, which is estimated between $800,000 and $1,000,000, and the Australian Capital Territory scales, which are the 1 July 2025 tables.

See how it works for every calculation step by step, and about for what the tool is and is not. If you find a figure that looks wrong, write to us at hello@myfinancialfuture.com.au.