Coast FIRE: When to Stop Saving and Still Retire

Picture a saver thirty years from retirement who wants a pot of 1,000,000 by the time they finish work. At an assumed 5 percent return after inflation, they could get there with roughly 231,000 invested today and nothing added afterward. Compounding does the rest. That single threshold is the whole idea behind coast FIRE, and the coast FIRE planner exists to find it for any target, timeline and rate you care to test.

The sections below explain what that number means, how it is worked out, and where it tends to help. There is a full worked example with real figures, a set of common scenarios, and the mistakes that most often throw the estimate off.

What is coast FIRE?

Coast FIRE is the moment your existing retirement savings become large enough to reach the target on their own. From that point, assuming a steady return after inflation, you could stop adding money entirely and let compounding carry the balance the rest of the way.

The name borrows from the wider FIRE movement, short for financial independence, retire early, but it describes a gentler milestone. Full independence means your investments cover your living costs today. It is narrower and arrives sooner: it asks only whether the retirement pot itself is on track, leaving day-to-day spending to your ordinary income.

Reaching it does not mean stopping work, and it does not force an early halt to saving either. It means the saving part of the job is, in principle, already done.

Why the coast FIRE number matters

Most retirement planning fixes on one distant figure and a monthly contribution meant to reach it. This threshold reframes that. Instead of asking how much to save each month for decades, it poses a sharper question: has enough already been set aside for the target to look after itself?

The answer often reveals more room than people expect. Someone who has quietly passed their coast number gains options. They could ease off contributions to retrain, move to a lower-paid but more rewarding job, or start a business, without derailing the retirement they have been building towards. The figure turns an abstract worry into something you can actually check.

It also travels well. Because the calculation rests only on time and an assumed real return, it does not lean on any one country's tax rules, pension limits or contribution caps. Those things differ everywhere and change often. The underlying arithmetic of compounding a balance towards a target does not.

How the coast FIRE number is calculated

The method is present value in plain clothes. You take the retirement target you eventually want and discount it back to today using the return you expect to earn after inflation. Whatever balance that leaves is the amount which, left untouched, could compound up to the target over the years available.

coast FIRE number = target / (1 + real return)^years

Where:

target = the retirement pot you are aiming for, in whatever currency you track your money
real return = the annual growth you assume after inflation, written as a decimal
years = the time between now and the date you plan to retire

The real return does most of the heavy lifting, and it is only ever an estimate. A cautious figure raises the number and builds in a margin; an optimistic one lowers it but leaves less room if markets disappoint. Because the rate is applied year after year, a small change to it moves the far end of the plan far more than the near end.

A worked example with real numbers

Take a saver thirty years from retirement, aiming for a target of 1,000,000, using an assumed real return of 5 percent. First, compound a single unit of money over the horizon: (1 + 0.05) raised to the power of 30 comes to about 4.32. That factor is how much each unit invested today could become across thirty years.

Now divide the target by it. 1,000,000 divided by 4.32 is roughly 231,377. So a balance of about 231,000 today could, at that steady rate, grow into the full million over thirty years with nothing further paid in. The coast FIRE calculator runs this same step for any target, horizon and rate, so you can drop in your own figures rather than the round ones used here.

It is worth sitting with what that means. The saver still has thirty years of earning ahead, but the retirement pot no longer needs feeding. Every contribution beyond this point becomes optional: a cushion against weaker returns, or a way to bring the retirement date forward, rather than a requirement to stay on course.

How to use the Coast FIRE planner

The coast FIRE planner asks for three things: the retirement target you want, the number of years until you retire, and the real return to assume. It returns the single figure that matters, the balance that could reach the target on its own, so you can hold it up against what you have already saved.

The most useful habit is to run the same target several times at different return assumptions. A plan that only holds together at 7 percent is a fragile plan; one that still works at 4 percent has room to breathe. Testing the range shows how much the threshold really depends on an assumption nobody can guarantee in advance.

Common scenarios

The same calculation bends to fit very different situations. A few come up again and again.

Longer horizon, younger saver

Time is the strongest lever in the whole equation. Stretch the horizon from thirty years to thirty-five and the same 1,000,000 target at 5 percent discounts to about 181,000. That is nearly a fifth lower, simply because compounding has five more years to work. A saver in their twenties can be technically on track with a strikingly small balance.

Conservative versus optimistic returns

Holding the horizon at thirty years, a cautious 4 percent assumption lifts the number to roughly 308,000, while an optimistic 7 percent drops it to about 131,000. That is more than a twofold difference from a three-point swing in a single input, which is exactly why testing several rates matters. A full FIRE calculation maps the wider journey to independence, where living costs enter the picture too.

Partial coasting

Few people flip from full saving to none overnight. A saver with 150,000 against a 231,000 threshold has a gap of about 81,000. Contributing for a few more years to close that gap, then easing right off, is a common middle path, and often a more comfortable one than an abrupt stop.

Recalculating after a setback

A weak run in the markets, or a year or two out of work, can pull a balance back below a threshold it had already passed. Re-running the number after such an event shows how far short it now falls, and how much extra saving, or extra time, would restore the plan. That picture is usually less alarming on the page than it feels in the moment.

What throws the estimate off

Treating the target as a fixed cash amount. Using a real return keeps the goal in today's money as inflation erodes value. Discount a target with a nominal rate instead and the plan quietly overstates itself.
Reaching for an optimistic return. A high assumption shrinks the number and flatters progress, which is precisely why it tempts. A more conservative rate produces an estimate that stands a better chance of surviving a poor decade.
Forgetting that coasting only covers retirement saving. The threshold frees you from feeding the retirement pot, not from paying this month's bills. Present-day living costs still come out of present-day income.
Setting it once and never revisiting. Balances, timelines and return expectations all drift. A number checked once at thirty says little at forty; the estimate is only as current as the last time it was run.

Coasting sits inside a small family of planning calculations, and each of these takes a neighbouring slice of the picture in more depth:

Coast FIRE calculator — discount any target back to the balance that could reach it unaided
FIRE calculator — model the fuller path to financial independence, where investments also cover living costs
Compound interest calculator — isolate how much of the growth towards a target comes from compounding rather than contributions

The coasting threshold is only one slice of a longer picture. The guide on what a financial life plan looks like year by year walks through the full projection, from a single yearly surplus to a net worth path.

Frequently asked questions

What is coast FIRE in simple terms?

It is the point at which retirement savings are already large enough to grow into a full retirement target without any further contributions, assuming a steady return after inflation. Someone who reaches this threshold could let compounding carry the balance to the goal by the target date. It differs from full financial independence, where investments also cover living expenses rather than the retirement pot alone. Reaching it does not require giving up work; it simply means that pot no longer depends on new money going in.

How is the coast FIRE number calculated?

The estimate discounts a future retirement target back to the present using an assumed real return. The formula divides the target by one plus the real return, raised to the number of years until retirement. For example, a 1,000,000 target thirty years away at 5 percent divides by about 4.32, giving roughly 231,000, the balance that could compound up to the target unaided. A coast FIRE calculator performs the same discounting step for whatever set of inputs a saver enters, so the round numbers here can be swapped for personal ones.

Can you stop saving early and still retire?

In principle, once a balance reaches this threshold, retirement contributions can stop while the pot keeps compounding towards the target. Whether that holds in practice depends on how closely real returns match the assumption, since a run of weaker years could leave a shortfall. Many people choose to stop saving only partially, easing contributions rather than halting them outright. Revisiting the estimate every so often, as balances and time horizons change, keeps the plan grounded in current circumstances rather than a single fixed calculation made years earlier.

What return assumption should the estimate use?

There is no single correct figure, which is why the estimate treats the real return as an adjustable input rather than a fixed promise. A lower assumption raises the number and builds in caution, while a higher one lowers it but leaves less margin if markets underperform. Long-run studies of diversified portfolios inform the ranges people commonly test, though past averages do not predict future results. Trying several assumptions, rather than settling on one, shows how sensitive the threshold really is to a number nobody can know ahead of time.

Is coast FIRE the same as being retired?

No — coasting means the retirement pot is on track to reach its target on its own, not that it can pay for daily life yet. Someone at their coast number usually keeps working to cover ordinary expenses, because those still come from earned income rather than from investments. Full financial independence is the later stage where the portfolio itself funds living costs and paid work becomes optional. It is best read as an early checkpoint on that longer road, marking the moment the saving pressure eases rather than the moment work ends.

Sources and methodology

The discounting method reflects standard compounding and present value principles, and every figure in the worked example and scenarios was checked arithmetically before publication. For long-run returns, safe withdrawal behaviour and how portfolios hold up over decades, two bodies of work are widely referenced. They are Morningstar's retirement and withdrawal rate research and the CFA Institute's material on the time value of money. Peer-reviewed studies on sustainable withdrawal rates add further context on the return ranges worth testing.

Putting it together

That single figure turns a vague sense of being on track into something testable. In the example above, a saver thirty years out could reach a 1,000,000 target with about 231,000 already invested and nothing more added, the rest left to compounding. Change the horizon or the assumed return and the threshold moves, sometimes sharply, which is the real value in running it more than once. Putting a personal target and a few return assumptions through the coast FIRE planner makes the concept concrete rather than theoretical.