FIRE Calculator — years until financial independence

The FIRE calculator exists to answer the question every financial independence plan eventually comes back to: not "what's my number," but "how many years until I actually get there." Enter your age, current invested savings, after-tax income, annual spending, and an expected real rate of return, and it simulates your portfolio year by year until it crosses the 25x-spending finish line.

What makes this different from a generic retirement projection is what it deliberately leaves out. It doesn't ask about expected raises, doesn't assume a fixed retirement age, and doesn't care what industry you work in. At Arb Digital we built it around a single variable that dominates every other input in the math: your savings rate. Everything else is secondary.

What the FIRE Calculator Does

The calculator first computes your savings rate — the share of your after-tax income you're not spending. It then works out your annual surplus (income minus spending) and your FI target (25 times your annual spending, matching the standard 4% withdrawal assumption). From there it runs a year-by-year simulation: your existing portfolio grows at your expected return, your annual surplus gets added on top, and the loop continues until your portfolio reaches the target. The number of loops is your years to FIRE.

How to Use It

1. Enter your current age and invested savings. Only count money actually invested — brokerage accounts, retirement accounts, index funds — not home equity or cash reserves you're not investing.
2. Enter after-tax income and annual spending. Be honest about both. The gap between them is what funds the entire plan.
3. Set an expected real return. 5% is a commonly used long-run real (after-inflation) return assumption for a diversified stock-heavy portfolio; some planners use 6-7%, others prefer 4% to be conservative.
4. Read your timeline. The big number is years to FI; the sub-line converts that into the actual age you'd hit it.
5. Change one input at a time. Bump your savings rate up 5 points and re-run it — you'll see immediately how much more that moves the needle than a return-rate change of the same size.

Why Savings Rate Is the Master Variable

Here's the finding that surprises almost everyone the first time they see it laid out: your savings rate alone — not your income, not your investment returns, not your career — determines your years-to-FI almost independent of how much you actually earn. A teacher saving 50% of a modest income and a surgeon saving 50% of a huge one reach financial independence in roughly the same number of years, because the math only cares about the ratio between what you keep and what you spend.

The logic is straightforward once you see it: your FI target is a multiple of your spending (25x), and your annual contribution is a function of your savings rate. A higher savings rate simultaneously shrinks the target (because you're spending less) and grows your annual contribution (because you're saving more) — a double effect that compounds fast. This is the entire intellectual foundation of the FIRE movement, and it's why it treats spending discipline as more powerful than income growth.

The Savings Rate vs. Years-to-FI Table

These figures assume no starting savings and a 5% real return, using the standard 25x-spending target — they illustrate the relationship, not a guarantee for any individual situation:

• 10% savings rate — roughly 51 years to FI
• 20% savings rate — roughly 37 years to FI
• 30% savings rate — roughly 28 years to FI
• 40% savings rate — roughly 22 years to FI
• 50% savings rate — roughly 17 years to FI
• 60% savings rate — roughly 12.5 years to FI
• 70% savings rate — roughly 8.5 years to FI

Notice how the curve accelerates — the jump from 10% to 20% saves about 14 years, but the jump from 50% to 60% saves about 4.5 years off a much shorter timeline. Every additional percentage point of savings rate matters, but the early gains from a very low starting point are often the largest single wins available to most households. The Trinity Study underlying the 25x figure is described in accessible terms by Investopedia, including its assumptions and limits: investopedia.com.

Lean FIRE, Fat FIRE, and Barista FIRE

The FIRE community splits the same core idea into a few named variants, mostly distinguished by how much the retiree plans to spend and whether work continues in some reduced form:

• Lean FIRE describes a plan built around a notably frugal budget, often $25,000-$40,000/year, which produces a smaller FI target and therefore a faster timeline, at the cost of less spending flexibility later.
• Fat FIRE is the opposite: a comfortable or even luxurious retirement budget, which raises the target substantially and stretches the timeline, but removes the need to compromise on lifestyle.
• Barista FIRE describes reaching a partial FI number and then covering the remaining gap with part-time or lower-stress work (the name references someone taking a lighter job, like at a coffee shop, mostly for health insurance and modest income) rather than fully replacing all spending from the portfolio.

All three use the exact same formula this calculator runs — they just plug in a different spending assumption, which is precisely why the spending input matters so much more than most people initially assume. Someone who runs this calculator with a Lean FIRE spending figure of $30,000/year and someone who runs it with a Fat FIRE figure of $100,000/year at the identical savings rate will see dramatically different timelines, purely because the target itself moved, not because anything changed about how hard either person is saving.

What the Return Assumption Actually Changes

Return assumptions matter, but less than most people expect relative to savings rate. Moving your expected real return from 5% to 7% shortens the timeline, but usually by a few years — not by decades. Moving your savings rate from 20% to 50% can cut the timeline by more than half. That asymmetry is the core reason FIRE planning conversations tend to focus so heavily on spending and saving behavior rather than chasing higher investment returns through riskier strategies.

This doesn't mean the return assumption is irrelevant — over multi-decade timelines even a 1-2 point difference compounds into real money — but it does mean it's the wrong lever to obsess over first. Chasing an extra percentage point of return usually means taking on meaningfully more investment risk (concentrated stock positions, leverage, speculative assets), while chasing an extra percentage point of savings rate usually means a spending adjustment that's fully within your control and carries no market risk at all. Run this calculator twice — once nudging the return up 2 points, once nudging the savings rate up 10 points — and compare the two results side by side. The gap in impact is usually the clearest argument for where to spend your energy.

What Counts as "Income" and "Spending" in This Calculator

To keep the model honest, use after-tax, take-home income as your income figure — not gross salary, since taxes are money you never actually get to save or spend. For spending, include every recurring cost: housing, food, insurance, debt payments, subscriptions, and discretionary spending, not just fixed bills. A common mistake is under-counting irregular expenses like annual insurance premiums, car maintenance, or holiday spending, which can understate your true spending by thousands of dollars a year and throw off both your savings rate and your FI target. If you're unsure, pull three to six months of actual bank and credit card statements and average them rather than estimating from memory.

Common Mistakes to Avoid

• Confusing nominal and real returns. If you use a nominal return (before inflation) but a target based on today's spending, you'll understate how many dollars you actually need — always keep both sides of the equation in the same terms.
• Ignoring lifestyle inflation. A savings rate that holds steady as income rises accelerates the timeline; a savings rate that stays flat while spending rises with every raise stalls it.
• Assuming a straight-line market. Real markets are volatile year to year even when long-run averages hold — this calculator shows an average-case trajectory, not a guarantee.
• Forgetting to update the plan. A windfall, a new dependent, or a career change can shift the timeline by years — re-run the numbers whenever something material changes.
• Treating the FI target as fixed forever. If your spending needs change between now and reaching FI, your target moves too.

Related Free Tools From Arb Digital

Pair this timeline with our FI number calculator to see the exact target figure behind the 25x math, our Coast FIRE calculator to find the point where you could stop contributing and still get there, and our savings rate calculator to dial in the input that matters most. Our net worth calculator is a good way to track progress along the way, and our compound interest calculator shows how the growth curve works in more detail. See the full free online tools hub for more.

Frequently Asked Questions

This tool provides general estimates for educational purposes only and is not financial, tax, legal, or medical advice. Figures are illustrative; consult a licensed professional for decisions.