FIRE stands for financial independence, retire early. A basic FIRE calculator turns an annual spending amount and a withdrawal-rate assumption into a portfolio figure. A more detailed version also estimates a path towards that figure using a starting balance, contributions and an assumed return.
Those are model inputs. A calculated result does not establish that a retirement plan will succeed, that an investment return will occur or that a particular withdrawal rate fits an Australian household.
The examples below use fictional AUD amounts and assumed percentages. None of the percentages is a recommended investment return or withdrawal rate.
How the target calculation works
A common formula divides annual spending by the assumed withdrawal rate written as a decimal. For fictional annual spending of AUD 48,000 and an assumed rate of 4%, the calculation is AUD 48,000 divided by 0.04. That gives AUD 1,200,000.
The formula is sometimes described as multiplying annual spending by 25. That is the same arithmetic because one divided by 0.04 equals 25.
Change spending to AUD 60,000 and keep the 4% assumption. The calculated figure becomes AUD 1,500,000. The additional AUD 12,000 of annual spending changes this modelled target by AUD 300,000.
Keep annual spending at AUD 48,000 but use a 3% assumption instead. The target becomes AUD 1,600,000. The AUD 400,000 difference comes entirely from changing one input.
These figures compare scenarios. They do not identify a correct target for any reader.
Spending needs a defined boundary
A spending input can describe today's household bills or a future annual budget. Those are different quantities. It also needs to say whether tax, housing, healthcare and irregular expenses are included.
Suppose the fictional AUD 48,000 includes an AUD 12,000 annual housing cost. Removing that cost produces AUD 36,000 and a 4% modelled target of AUD 900,000. The lower result follows from removing an expense, not from the calculator discovering a better investment outcome.
A one-off expense creates another distinction. Adding a fictional AUD 20,000 purchase to every future year's spending is different from treating it as a single dated outlay. A simple constant-spending model does not automatically make that distinction.
An expense tracker can document what happened in past periods. It does not establish the cost or duration of future spending.
Time and investment returns add assumptions
A growth projection normally needs a starting balance, an ongoing contribution and a return assumption. Compounding applies a mathematical pattern to those inputs.
For example, AUD 100,000 growing at an assumed constant 5% for ten years, without contributions, fees or tax, becomes approximately AUD 162,889. At an assumed constant 3%, it becomes approximately AUD 134,392. Both are calculated scenarios, not predicted account balances.
Actual investment returns vary between periods. The order of returns also affects a portfolio when money is being withdrawn. A straight growth curve does not represent every possible sequence of losses and gains.
Inflation changes what a dollar buys over time. A model needs to identify whether its spending and return inputs use current purchasing power or future dollars. A currency selector alone does not perform that adjustment.
Australian accounts add access questions
Australian retirement records can include super, assets outside super and other income sources. A combined balance does not establish that all those amounts are available on a chosen early-retirement date. Super has access conditions that a basic portfolio formula does not test.
FinTarget's FIRE calculator models the inputs shown on its form. It does not calculate Australian tax, determine super access, assess government benefits or simulate uncertain return paths.
Moneysmart publishes assumptions for its own retirement and savings calculators, illustrating why different tools can produce different results. A comparison is meaningful only after the spending period, contribution timing, return basis and omitted costs have been identified.