Coast FIRE is the most appealing idea in the whole FIRE canon: at some point your invested pot is large enough that compounding alone carries it to your retirement number, and everything you add after that is optional. Reach the coast point and you can drop to a job that merely covers the bills, stop contributing entirely, and still retire on schedule.
Every coast calculator you will find computes this the same way. It takes your total invested pot, grows it at a fixed rate until your retirement age, and checks whether it clears your target. That arithmetic is correct in the United States, where a 401(k) and a taxable brokerage account both eventually spend the same way. In Europe it quietly asks the wrong question, because a large share of most people's invested wealth sits in a pension that is locked by law until an access age.
The short version:
- Coasting is not free, and the price is years. For the household below it moves the earliest stop date from mid-2034 to late 2039, so a little over five years.
- The locked pension barely moves the coast date, which is the surprise. Ten months, in this case.
- It does roughly halve how close you actually are. The "could you stop today" figure drops from 66% to 38% once the lock is modelled, because money you cannot reach for 25 years cannot fund a retirement that starts now.
- So the number a coast calculator flatters most is not your date, it is your progress. If you are using progress to decide whether to downshift this year, that is the number you were relying on.
The household
One worked example, run on the public forecast calculator. It uses the same projection engine as the Krosos app, so every figure below is a scenario you can open, edit and disagree with.
| Age | 40 (born 1986) |
| Net take-home | €3,600 a month |
| Living costs | €2,400 a month |
| Cash | €20,000 |
| Stocks and funds | €150,000 |
| Pension | €400,000, locked until January 2051 (age 65) |
| Retirement spending | €2,400 a month, in today's money |
| Withdrawal rate | 3.5% |
Two assumptions worth stating rather than burying. Growth is 6% nominal on stocks against 2% inflation, so 4% real, which is more conservative than the calculator's own 7% default. And the pot is deliberately pension-heavy: €400,000 locked against €170,000 reachable. That is not an exotic case in Europe, it is what a decade of salary sacrifice, employer matching and tax relief produces, and it is precisely the shape that coast arithmetic handles worst.
Three runs
Run 1: keep saving. The €1,200 monthly surplus keeps going into stocks, a 33% savings rate. Open this scenario.
Could stop: July 2034, age 48. Stop-now progress: 38%.
Run 2: start coasting today. One input changes: take-home drops to €2,400, exactly covering living costs, so the surplus is zero and nothing is ever added again. Open this scenario.
Could stop: September 2039, age 53. Stop-now progress: 38%.
Run 3: the same coast, with the pension treated as ordinary money. Again exactly one input changes: the January 2051 unlock date is removed, so the pension is spendable from day one, which is what a conventional coast calculator assumes. Open this scenario.
Could stop: November 2038, age 52. Stop-now progress: 66%.
| Run | Could stop | Stop-now progress |
|---|---|---|
| Keep saving €1,200 a month | July 2034 (48) | 38% |
| Coast, pension locked | September 2039 (53) | 38% |
| Coast, pension counted as free money | November 2038 (52) | 66% |
What the three runs actually say
Coasting costs this household five years and two months. That is the honest headline, and it is the trade coast FIRE is really offering: not a free lunch, but years of your life bought with a lower-stress decade. Worth it for many people. Worth knowing the price of.
The lock costs ten months on the date, and that is genuinely small. It surprised me, and the reason is worth understanding. The calculator spends your reachable money first and treats the pension as the last thing it touches, which is what a sensible person does anyway. By the time this household stops in 2039, the unlock is only twelve years out and the taxable side has had thirteen years of compounding to build a bridge. The lock is a real constraint, but it is a constraint that gets weaker every year you leave it alone.
Progress is where the distortion lives. Stop-now progress asks a different question: not "when could I stop" but "how big is my pot compared to the size it would need to be for me to stop today". Today, this household's €400,000 pension is 25 years from being spendable, so it can contribute nothing at all to a retirement starting now. Model that and they are 38% of the way there. Ignore it and they look 66% of the way there. The date moved by ten months; the gauge nearly doubled.
That gap matters because of how the coast decision actually gets made. Nobody reads a date in 2039 and hands in their notice. They look at how close they are, decide the finish line is near enough that compounding can take it from here, and downshift. A progress figure that counts locked money is telling them to make that call years too early.
One last detail worth noticing: runs 1 and 2 report identical progress, 38% in both. Of course they do. Progress is a statement about the pot you have today, and today is the same in both runs. Saving changes your date. It does not change how close you are right now. Any tool that shows those two numbers moving together is not measuring what it claims to.
Doing this with your own numbers
The parameters that matter, and the ones people get wrong:
- Set the unlock date, not just the pension balance. In the calculator it is the pension access field. Leave it empty and you have built run 3, which is the flattering one.
- Model coasting as take-home equal to expenses, rather than by zeroing your investment split. That produces a genuine zero surplus instead of quietly routing the leftover into cash.
- Use your own return assumption. The 7% default is optimistic against a 2% inflation figure. We used 6% here and said so.
- Zero the asset classes you do not hold. The calculator ships with sample balances in cash, money market funds and crypto, and inheriting them silently inflates your pot.
The sibling piece to this one, retiring before pension age, works the other half of the same problem: what the lock does when you stop earning entirely rather than merely stop saving. The withdrawal-rate assumptions underneath both, and what European taxes do to them, are in the 4% rule in Europe.
What this leaves out
- Pension withdrawals are usually taxed as income, and this model does not do that. The calculator applies one capital-gains regime to everything. Real pension drawdown is taxed differently almost everywhere in Europe, so the after-unlock money is worth somewhat less than shown. The bridge-side arithmetic, which is the subject here, is unaffected.
- Coasting assumes you can actually get the lower-paid job, and keep it. A model that drops your take-home to exactly your expenses for thirteen years is describing a labour market outcome, not a financial one. It also leaves no room for a bad year.
- These are single straight-line paths. Real markets do not deliver 6% a year in order. The calculator's Monte Carlo mode runs 500 simulated markets around the same plan and reports how often it survives, which is the more honest way to read any of these dates.
- Access rules are specific to your scheme and your country. Protected ages, early-access provisions and the tax cost of taking money early all vary. January 2051 here is a typical age-65 unlock, not a promise about yours.
- Krosos does not model a wealth tax. If you are in a jurisdiction that taxes the stock rather than the gain, these runs are missing a real drag.
As always: these are estimates from your own assumptions, for planning. Not financial advice.