The question "when can I retire?" deserves an answer built from your real numbers, not a legal age set by the government. With the right calculation you can place your financial freedom date to within a few months. Here are the formulas and some worked examples.
The logic of the calculation
Your retirement date is where two lines cross. The first is the growth of your wealth: what you have, plus what you save, plus compound returns. The second is your target, the amount that lets you live off your investments. The day the first line reaches the second, you are free.
The target itself comes from the 4% rule:
Target = annual expenses × 25
How long it takes to get there depends on three things: your starting wealth, your monthly savings, and the average return on your investments.
The full formula
To work out how many years (n) it takes to reach a target (T):
T = P₀ × (1 + r)ⁿ + S × 12 × [((1 + r)ⁿ - 1) / r]
That does not solve cleanly for n, so in practice you iterate, or you let a simulator like IgniFI do it. The examples below give you the shape of it.
Worked examples
Age 30, $20,000 saved, target $750,000 at 7%
| Monthly Savings | Years Needed | Retirement at |
|---|---|---|
| $300/month | ~35 years | 65 |
| $500/month | ~30 years | 60 |
| $800/month | ~26 years | 56 |
| $1,200/month | ~22 years | 52 |
| $1,800/month | ~19 years | 49 |
Tripling your savings does not just shave a year or two. It pulls the date forward by more than a decade, because every extra euro compounds for the whole journey.
Age 40, $80,000 saved, $1,000/month, target $750,000
| Annual Return | Years Needed | Retirement at |
|---|---|---|
| 4% (bonds/stable funds) | ~25 years | 65 |
| 6% (balanced allocation) | ~21 years | 61 |
| 7% (diversified ETFs) | ~19 years | 59 |
| 9% (equities + crypto) | ~17 years | 57 |
Return matters a lot. The catch is that chasing a higher return means accepting more risk, while saving more is something you control directly.
Age 35, $150,000 saved, $1,500/month, target $1,000,000 at 7%
This profile reaches the target in about 18 years, so retirement at 53. Cut the target spending to $30,000 a year, which drops the target to $750,000, and it falls to roughly 14 years, retirement at 49. Spending less does double duty: it lowers the finish line and speeds you toward it at the same time.
The quiet power of a couple of points of return
People underrate the gap between returns that look similar. Here is $10,000 left to grow for 20 years:
| Annual Return | Final Capital |
|---|---|
| 3% (savings account) | $18,061 |
| 5% (balanced funds) | $26,533 |
| 7% (World ETF) | $38,697 |
| 9% (aggressive equities) | $56,044 |
| 11% (S&P 500 best case) | $80,623 |
The jump from 5% to 7% looks minor on paper and produces 46% more capital over 20 years. On a $750,000 target that is years of your life.
Your savings rate is the master variable
More than your income, the share of it you keep decides when you stop working.
Starting from zero, a target of 25 times annual spending, a 7% real return a year. The curve is not straight: the first ten points of savings buy far fewer years than the next ten, because saving more also lowers the amount you have to reach. Orders of magnitude, not a forecast.
A 50% rate is realistic for plenty of people with a decent income and a controlled lifestyle, and it gets you to FIRE in 17 years whatever you earn. That last part surprises people. The maths cares about the percentage, not the salary.
Four realistic scenarios
Traditional retirement at 62 to 67. For people who want maximum income and security. Invest regularly through retirement accounts, lean on employer matching, and aim for $200,000 to $400,000 on top of the state pension. The trade-off is that you stay dependent on the public system.
Semi-retirement at 50 to 55 (Barista FIRE). For people who want to slow down without stopping. Build capital that covers half to two thirds of your spending, top up with light work, so roughly $500,000 to $600,000 plus $1,000 to $1,500 of side income. Much more reachable than full FIRE.
Financial independence at 45 to 50 (classic FIRE). For higher earners or high savers. Fill the tax-advantaged accounts, add a taxable account, buy passive ETFs steadily, and aim for $750,000 to $1,000,000 over fifteen to twenty focused years.
Lean FIRE before 40. For people happy to live on under $20,000 a year. Push the savings rate to 60 or 70 percent and aim for $400,000 to $500,000. It works, but it asks for a genuinely frugal life over the long haul.
Biases that distort your projection
The most common one is using 10% returns because that is the S&P 500 headline. That number ignores inflation of around 3% a year and assumes the future copies the past. Use 6 to 7% real for planning.
Tax drag is the next trap. A $1,000,000 portfolio returning 7% does not hand you $70,000 to spend, because withdrawals get taxed. Use your real after-tax rate.
Then there is expense inflation. Spending $3,000 a month today can feel like $4,000 in fifteen years at 2% inflation, so push your target up by 20 to 30%. And present bias makes us assume today's life is permanent, when children, paid-off mortgages and health all move the numbers. Build an optimistic, a central and a pessimistic version rather than a single line.
How to pull the date forward
In rough order of impact. Raising your income and investing the raise is usually the biggest lever, often more than anything else. Cutting fixed costs comes next: a cheaper city, a cleared mortgage or losing a car payment can free $400 to $800 a month overnight. Tax optimisation helps too, since at a 30% marginal rate, $3,000 into a retirement account costs you $2,100 after tax. Improving returns matters but brings volatility, and avoiding expensive mistakes, like 1 to 2% fund fees or failed active trading, quietly protects the rest.
Run your own numbers
You need four figures: your current net worth, your real monthly savings, your target annual spending in retirement, and a sensible expected return for your allocation. Put those into IgniFI and it sets your FIRE target and works out the date. The built in Monte Carlo also shows the pessimistic and optimistic versions based on historical market behaviour.
FAQ
I'm starting at 45 with nothing saved. Is it too late? No. At $1,500 a month and 7%, you reach about $450,000 in 17 years, by 62, a solid base on top of your state pension. The best time to start was years ago. The second best is now.
Should I count my home in my FIRE wealth? Usually not. It does not produce income unless you rent part of it. It can still lower your FIRE target, though, because owning it outright cuts your retirement spending.
How do I handle market uncertainty? Plan with a conservative return, 6% rather than 8%, and hold one to two years of expenses in cash as you near the date. The IgniFI Stress Test runs your portfolio through real crises like 2008, the dot-com bust and COVID.
My savings vary a lot month to month. What do I use? A 12-month average, then plan with about 80% of it so the lean months do not derail you.