Curious whether your current savings and habits will let you retire early? This post explains the idea behind the FIRE movement (Financial Independence, Retire Early), why saving and investing matter, how inflation eats away at uninvested cash, and what the calculator on this page actually does — plus practical tips for using it and next steps.

What is the FIRE movement?

FIRE stands for Financial Independence, Retire Early. It’s a set of personal-finance ideas and habits that aim to build enough savings and investments so that a person can stop working (or greatly reduce paid work) long before traditional retirement age.

Common FIRE styles:

• Lean FIRE — very frugal, minimal expenses, smaller portfolio required.
• Fat FIRE — comfortable lifestyle in retirement; requires a larger portfolio.
• Barista / Coast / Semi-FIRE — part-time work or guaranteed income (pension, part-time job) covers some expenses so you don’t need to fully withdraw from investments.

The core idea is simple: spend less than you earn, save the difference, invest it, and let compounding returns and disciplined frugality build a portfolio large enough to cover future expenses.

Why saving (and investing) matters

Saving money is the first step — but saving alone isn’t usually enough. Money kept as cash loses purchasing power over time because of inflation. Investing (in a diversified portfolio of stocks/bonds/etc.) gives your savings a chance to earn returns that can outpace inflation and grow your net worth.

Two short examples:

• If you keep €10,000 as cash and inflation averages 3% per year, the purchasing power of that €10,000 after 20 years will be roughly €5,536.76 in today’s euros — in other words, almost half its real value. (Calculation: 10,000 ÷ 1.03²⁰ ≈ €5,536.76.)
• If instead you invest €10,000 and it grows at 5% per year, after 20 years it would grow to about €26,532.98 (10,000 × 1.05²⁰ ≈ €26,532.98).

That contrast shows two truths: inflation erodes uninvested cash, and compound returns can materially grow invested capital.

What “early retirement” really means

Early retirement doesn’t always mean complete stop to work. For some people it’s:

• fully stopping paid employment, living off investments;
• switching to lower-stress or part-time work;
• having passive income sources (rental, dividends, pension) that cover expenses.

Your definition of retirement affects how large a portfolio you need, because your expenses and any ongoing income determine the withdrawal power of your assets.

A common rule of thumb used by many in FIRE is the 4% rule: a safe initial withdrawal rate of about 4% of your portfolio per year (adjusted for inflation). Using that rule, the portfolio size needed = annual expenses ÷ withdrawal rate. Example: if your expenses are €30,000 / year and you use a 4% withdrawal rate, you’d need roughly €30,000 ÷ 0.04 = €750,000.

How inflation “eats” uninvested money

Inflation is the long-term rise in prices. If your money sits in a bank or under a mattress earning less than inflation, your real buying power declines. That’s why the calculator lets you enter both:

• a nominal ROI (return on investments) and
• an inflation rate — so you can see how nominal returns translate into real value and how expenses grow over time.

What this calculator does (and how to use it)

The calculator simulates two phases:

1. Accumulation phase — starting from your current portfolio, it projects yearly:
   • income (growing by your expected income increase),
   • expenses (growing by inflation),
   • investment returns (ROI),
   • annual savings added to the portfolio,
   • end-of-year net worth.
     The simulation stops when the portfolio is large enough that (portfolio × withdrawal rate) ≥ that year’s expenses — meaning the portfolio can theoretically support your expenses using the chosen withdrawal rate.
2. Retirement phase — starting from the year you reach FIRE, the calculator projects yearly:
   • income after retirement (if any) and its growth,
   • expenses continuing to grow by inflation,
   • investment returns applied to the portfolio,
   • portfolio withdrawals (implicitly via the “income − expenses” part of net change),
   • net worth evolution for up to 70 years (configurable inside the tool).

Important inputs you provide:

• Current annual income and expected annual income increase — lets the tool grow future income.
• Current annual savings — how much you add to investments each year while accumulating.
• Current annual expenses — your baseline cost of living; the stopping condition is based on covering this number.
• Current portfolio value — investments you already have.
• Annual ROI (before inflation) — the expected nominal return your portfolio will earn per year.
• Withdrawal rate — e.g., 4 means 4% (0.04).
• Inflation — yearly inflation rate (e.g., 3%).
• Does income stop in retirement? — if not, you can give expected income after retirement (e.g., pensions, part-time work).

Outputs you’ll get:

• Years until retirement (possibly fractional, interpolated for precision).
• Portfolio value at retirement required to support expenses at the chosen withdrawal rate.
• Two tables (accumulation and retirement) and corresponding line charts showing net worth over time, ROI contribution, annual changes, and other details.
• CSV export so you can analyze the yearly tables offline.

Key assumptions & limitations (please read!)

The calculator is a useful planning tool, but it simplifies reality. Important assumptions and limitations include:

• Constant rates: income growth, ROI, and inflation are assumed constant (fixed percentage each year). Real life is variable year-to-year.
• Return timing and compounding: returns are applied annually in the way modeled by the tool; different compounding assumptions or intra-year cash flows change results.
• No taxes or fees: the base model does not include income taxes, capital-gains taxes, transaction costs, or annual management fees. These can materially change how quickly your portfolio grows and how long it lasts.
• Sequence-of-returns risk: the order in which returns occur matters a lot in retirement. Two scenarios with the same average return can have very different outcomes if bad returns happen early in retirement. The simple deterministic simulation does not model sequence risk.
• No unpredictable life events: one-time large expenses (medical, home repairs, supporting family, etc.) are not modeled unless you manually modify inputs or add such features.
• Withdrawal behaviour: the tool models net changes but does not implement advanced withdrawal strategies (variable withdrawals, dynamic glidepaths, floor-and-ceiling rules, etc.).

Because of these simplifications, use the calculator for planning and exploration, not as absolute forecasting. Consider running sensitivity checks (change ROI, inflation, savings rate) and, for critical decisions, consult a financial planner.

Practical tips for using the calculator

• Run multiple scenarios: try conservative vs optimistic ROI and inflation assumptions (e.g., ROI 4% vs 7%; inflation 2% vs 4%). See how sensitive your retirement year is to these inputs.
• Watch the savings number: increasing annual savings by even a modest amount can dramatically shorten the path to FIRE through both direct contributions and compound growth.
• Try different withdrawal rates: 4% is a common rule of thumb, but some prefer 3.5% for greater safety; others might accept 4.5% if they’re comfortable with higher sequence-of-returns risk.
• Account for taxes: if you have large taxable accounts or high tax rates on withdrawals, simulate lower net ROI or add a tax/fee buffer.
• Consider emergency buffer: keep a separate cash emergency fund to avoid having to sell investments in down markets.

Features you might want to add (advanced ideas)

If you find the calculator helpful, consider augmenting it later with:

• Monte Carlo simulations (to show probability of success under random return sequences).
• Tax and fee modeling (to make outputs more realistic).
• Multiple income sources (pensions, rental income, part-time work starting at different years).
• Overlay charts to compare scenarios (e.g., +1% savings, +2% ROI).
• A “required savings” or “how much to save monthly” calculator that converts target years into monthly/annual saving goals.

Final note — how to use the result

Treat the calculator as a compass, not a guarantee. Use the tables and charts to:

• set concrete targets (portfolio size and annual savings),
• test “what-if” scenarios (what if inflation is higher? what if I save €X more?), and
• plan practical next steps (increase savings rate, reduce expenses, tax-efficient investing).

If you like, I can add additional educational text to the calculator page (for example — a short explanation of the 4% rule, tips on tax-efficient accounts, or a short glossary). Want me to add any of those?