Can You Afford to Retire Early? Running the FIRE Numbers

The idea that will not leave you alone

There is a moment in every working person’s life — usually around 35, sometimes earlier — when the thought arrives: what if I did not have to do this forever? Not hating the job necessarily, just wondering whether there is a number, a specific amount of money, that would make working optional rather than mandatory.

That question is the core of the FIRE movement — Financial Independence, Retire Early. During my years in wealth management, I watched it evolve from a fringe idea on internet forums into a serious financial planning goal for a growing number of clients. The maths behind it is surprisingly simple. The discipline required to execute it is anything but.

The basic premise is this: if you can accumulate a portfolio large enough that its investment returns cover your annual living expenses, you no longer need employment income. You are financially independent. Whether you then choose to stop working, switch to something you love, or just enjoy the security of knowing you could walk away — that is up to you.

What is your FIRE number?

Your FIRE number is the total investment portfolio you need to sustain your lifestyle indefinitely. The most commonly used guideline is the 4% rule, derived from a 1998 study: if you withdraw no more than 4% of your portfolio in the first year of retirement and adjust for inflation annually, your money has historically lasted at least 30 years.

Working backwards: if you need $40,000 per year to cover your expenses, your FIRE number is $40,000 divided by 0.04, which equals $1,000,000. If you need $60,000, it is $1,500,000. If you need $80,000, it is $2,000,000.

The formula is elegant but the inputs require honesty. You need to know what your annual expenses actually are — not your current income, but your actual spending in retirement. Many FIRE aspirants find they can live on significantly less than they earn, especially once commuting costs, work wardrobe expenses, and convenience spending disappear.

Let’s use the FIRE Calculator to find your personal target.

That number might look impossibly large or surprisingly achievable depending on your current expenses and savings. Either way, it is the destination. The next question is how quickly you can get there.

How your savings rate determines your timeline

In traditional retirement planning, you work for 40 years and save slowly. In FIRE, the savings rate is the primary lever. Someone saving 10% of their income might need to work 40+ years to reach financial independence. Someone saving 50% can potentially get there in about 17 years. At 70%, the timeline shrinks to roughly 8 to 10 years.

The relationship is not linear — it is exponential, because every dollar you save does double duty. It increases your investment balance and simultaneously proves you can live on less, which lowers your FIRE number. A person earning $100,000 who saves $50,000 and lives on $50,000 needs a much smaller portfolio than someone earning the same amount who saves $10,000 and lives on $90,000.

Let’s use the Retirement Calculator to model your timeline based on your current age, savings, and contribution rate.

Pay close attention to how the timeline changes when you adjust the savings rate. Even a five-percentage-point increase — from 20% to 25% of income — can shave years off your working life. This is the insight that motivates FIRE adherents to optimise their expenses: every dollar cut from your monthly spending accelerates the timeline from both directions.

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The power of compound growth

The reason FIRE works at all is compounding. Your investments generate returns, those returns generate their own returns, and over time the growth becomes self-reinforcing. The earlier you start and the more consistently you contribute, the more dramatic the compounding effect becomes.

Let’s use the Compound Interest Calculator to visualise how your money grows over different timeframes.

Try comparing a scenario where you invest $1,000 per month for 15 years versus 25 years at a 7% average return. The difference is not proportional — the last ten years produce dramatically more wealth than the first ten, because by then your existing portfolio is generating substantial returns on its own. This is why starting early matters so much, and why even small contributions in your twenties can have an outsized impact on your FIRE timeline.

Modelling your investment contributions

The final piece of the puzzle is connecting your savings rate to specific investment contributions and seeing whether the projected growth hits your FIRE number within your target timeframe.

Use the Investment Calculator to model your contributions and projected portfolio growth.

If the numbers show you reaching your FIRE number at age 50, ask yourself: is that realistic given your current spending, income trajectory, and risk tolerance? If you are relying on aggressive market returns to make the timeline work, build in a margin of safety. Markets do not deliver 10% every year — there will be downturns, and your plan needs to survive them.

The honest conversation about FIRE

I would be doing you a disservice if I presented FIRE as universally achievable or without trade-offs. A few realities worth considering:

Income matters. FIRE is substantially easier on a high income. Saving 50% of a $150,000 salary leaves $75,000 to live on, which is comfortable. Saving 50% of a $40,000 salary leaves $20,000, which is extremely difficult in most areas. FIRE content online skews heavily toward high earners, and the timelines they share are not representative.

The 4% rule has limitations. It was designed for a 30-year retirement. If you retire at 35, you need your money to last 50 to 60 years, which is a different proposition. Many early retirees use a more conservative 3% or 3.5% withdrawal rate, which increases the required portfolio size.

Healthcare is expensive. If you retire before you are eligible for government healthcare programmes, private health insurance becomes a significant expense that must be factored into your annual spending number.

Life changes. Your expenses at 35 may not reflect your expenses at 55. Children, ageing parents, health issues, relocations — life has a way of revising your budget without asking permission.

None of this means FIRE is not worth pursuing. Financial independence — even if you never fully stop working — provides options, security, and peace of mind that are genuinely life-changing. But the plan needs to be built on realistic numbers, not optimistic projections and aspirational spreadsheets.

Run the calculators with honest inputs. Know your FIRE number, your timeline, and the savings rate required to get there. Then decide how much of that trade-off you are willing to make. The answer does not have to be all or nothing.

Disclaimer: This article is for informational and educational purposes only and does not constitute personalised financial advice. Investment returns are not guaranteed, and past performance does not predict future results. Consider consulting a qualified financial adviser before making significant changes to your investment strategy.

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