Coast FIRE Calculator Australia

How Coast FIRE works

Coast FIRE is reached when current investments, compounded forward at the expected return rate without any further contributions, equal or exceed the amount needed to fund the target retirement spend. Past the coast threshold the model shows the existing balance alone reaches the target, further contributions stop being mathematically required, assuming returns track the chosen expected rate.

The math is straightforward: divide your inflation-adjusted retirement spend by your safe withdrawal rate to get the FIRE target at retirement, then check whether your current balance compounds to that target by the retirement age you have chosen.

The Australian twist: super preservation

In Australia, super cannot be accessed until preservation age, which is 60 for everyone born after 1 July 1964. This matters because Coast FIRE is often quoted as a single number, but in Australia the question is two-part:

• Have you coasted overall? Will your combined super and non-super balances compound to your total FIRE target?
• Can you bridge to preservation? If you plan to retire before 60, do you have enough non-super to fund the gap years before super unlocks?

Both must be true to actually stop work at the age you have chosen. This calculator surfaces the bridge check whenever your retirement age is below the active preservation age.

Worked example

Sam is 40 with $400,000 in super and $100,000 in non-super investments. They want to retire at 60 with a target spend of $60,000 per year (today's dollars). They use a 7% expected return and 2.5% inflation. The 4% safe withdrawal rate gives an inflation-adjusted FIRE target at 60 of roughly $2.46 million ($60,000 × 1.025^20 ÷ 0.04).

Their current $500,000 combined, compounded at 7% for 20 years, grows to roughly $1.93 million, short of the $2.46 million target. Sam has not coasted yet. To check: how much would Sam need today to reach exactly $2.46 million at 60? About $635,000. Sam needs another $135,000 in their portfolio to coast right now.

Sam is not coasting today, but they do not need to make up that $135,000 in one go. If Sam saves $30,000 a year (split across super and non-super), the calculator walks year by year and finds the first age where the projected balance is large enough to coast the rest of the way. With these inputs Sam reaches Coast FIRE around age 47. From that point Sam could stop contributing and the existing balance alone would compound to the $2.46 million target by 60. Saving $40,000 a year instead pulls the Coast age earlier; saving less pushes it later.

Because Sam is retiring at 60 (the preservation age), the bridge check does not apply, and savings flow straight to super.

Worked example: retiring before preservation

Lina is 35 with $200,000 in super and $100,000 in non-super, and she wants to retire at 55 with a $60,000 spend. The bridge years (55-59) cost about $452,000 in present-value terms at retirement (this is what the calculator computes from the inflated annual spend, discounted at the expected return rate). Her FIRE target works out to $1.5M in today's dollars or $2.46M at age 55 once inflation is folded in.

If Lina saves $50,000 a year, the calculator routes early savings to non-super first to fund the bridge. The front-loaded years build up the non-super pool until it projects to cover the $452,000 requirement at retirement. After that, every subsequent year of savings flows to super. Lina's Coast age comes out at 44. From that point Lina could stop contributing entirely; both her super and her non-super (which now covers the bridge) compound to retirement, hitting the $2.46M target at 55 with the bridge fully funded.

The full ProjectFi planner refines this with super contribution caps, salary sacrifice tax savings, partner balances, and year-by-year iteration; the simple Coast calc gives the directional answer.

Sources and references

Australian super preservation age: ATO preservation age table. Safe withdrawal rate research: original Trinity Study (Cooley, Hubbard, Walz 1998) and the broader FIRE community consensus on 3.5%-4% drawdown for 30+ year horizons.

Want to see this calculation in your full FIRE plan, with tax, Age Pension, and Monte Carlo sensitivity included? The ProjectFi planner takes you all the way to a year-by-year projection.