Financial independence is the point where what you have invested can cover what you spend, without you working. FIRE — financial independence, retire early — is the practice of getting there decades before the conventional retirement age, and the arithmetic behind it is far simpler than the amount written about it suggests.
It rests on one number: the share of your income you keep. Not how much you earn. Someone earning a great deal and spending nearly all of it can be further from independence than someone on half the salary who keeps a third of it, because spending sets both how fast you save and how large a pot you need. This calculator shows that directly.
This is for people who are already saving a meaningful share of their income and want to know what it buys them. If you are still clearing high-interest debt, that comes first, and this projection will only tell you a discouraging story about a situation you are already fixing.
This calculator needs JavaScript. The rule of thumb without it: multiply your annual spending by 25. That is roughly the pot you need at a 4% withdrawal rate. Then work out what share of your income you save each year — at 10% it takes around 50 years, at 25% around 30, at 50% around 17, and at 65% around 10.
Why the savings rate is the whole story
Two things happen when you spend less. The obvious one is that you have more left to invest. The one people miss is that the target itself falls, because the target is nothing more than your annual spending multiplied out — at a 4% withdrawal rate, twenty-five times it.
Cutting your spending by a thousand a year therefore both adds a thousand a year to your investing and takes twenty-five thousand off the pot you are trying to build. Earning an extra thousand and spending it all does neither. That asymmetry is why savings rate, not income, sets the timeline, and why the sensitivity table above shows spending moving the date further than an equivalent change in investment returns.
A worked example
Someone aged 30, spending $50,000 a year, with $100,000 invested and adding $25,000 a year at a 7% return. Those are the figures the form above is already carrying, so you can check this against the calculator directly — including “let spending rise with inflation”, which is on by default and does most of the work here.
Because the $50,000 rises each year, the target is not 25 times today’s spending but 25 times what it will cost in the year they stop: $2,434,750. They reach it in 27 years, at age 57. Turning inflation off drops the target to $1,250,000 and the answer to 19 years — which is the figure most retirement arithmetic quietly assumes, and the reason it flatters itself.
Two levers move that date, and on this tool they are worth exactly the same. Adding $5,000 a year to the contribution brings it forward two years, to 25. Cutting annual spending by $5,000 also brings it forward two years, by lowering the target rather than raising the balance.
Change both together and you get four years, to 23. That is the case worth understanding, because it is the realistic one: money you stop spending is money you can invest, so a genuine $5,000 cut should raise the contribution by $5,000 as well. The calculator treats the two fields as independent and will not do that for you — edit both, and what you are looking at is your savings rate rather than either number on its own.
What the 4% rule actually says
The withdrawal rate comes from research into how much could historically be taken from a portfolio each year without exhausting it over a 30-year retirement. Four per cent held up across most historical periods, which is why it became the default.
It is a rule of thumb, not a guarantee, and it was derived for a 30-year horizon. Someone stopping work at 45 is planning for considerably longer than that, which is the argument for using a lower rate — 3.25% to 3.5% is a common adjustment, and it raises the target substantially. The calculator lets you change it, and it is worth seeing what your own number does at 3.5%.
Where this model is weakest
It assumes a steady annual return, and real markets do not deliver one. The order matters as well as the average: a severe fall early in retirement does far more damage than the same fall twenty years in, because you are selling units to live on while they are cheap. This is called sequence-of-returns risk, and no single-line projection can show it.
It also ignores tax, which is not a small omission — where you hold investments can shift the date by years. And it assumes your spending and income stay flat in real terms across decades, which for most people is the least realistic assumption in the whole model.
Treat the output as a way to compare choices rather than as a date to plan around. The comparison is robust even where the absolute number is not.
The compound interest calculator runs the same arithmetic pointed at a different question: not when the balance becomes enough, but how much of it you never had to earn. It is worth seeing alongside this one, because the answer to both is driven by the same thing.
If the contribution line is the one you want to move, the subscription audit and the debt payoff calculator both work on the same figure from the other end. Our wealth and working guides cover the earning side.