Verified calculation
Coast FIRE calculator
How much would you need invested today for it to reach your retirement target on its own — without you adding another penny?
Where you are now
What you are assuming
in retirement
= 25.0× spending
after inflation
0 = coasting now
What the arithmetic says
How this was calculated
Two steps, both from the compound interest formula.
target = yearly spending ÷ withdrawal rate
coast number = target ÷ (1 + real return)years to retirement
On your figures: $40,000.00 ÷ 4% = $1,000,000.00, the amount you would need invested at 60. Discounted back over 30 years at 5% a year, that is $231,377.45 today.
The projection steps month by month at the effective monthly rate, (1 + 5%)^(1/12) − 1, rather than dividing the annual figure by twelve. A stated annual return compounds to that figure over the year, so dividing would overstate a long projection.
| Age | Year | Projected | Coast target | Coasting |
|---|---|---|---|---|
| 30 | 2026 | $100,000.00 | $231,377.45 | — |
| 31 | 2027 | $111,136.29 | $242,946.32 | — |
| 32 | 2028 | $122,829.38 | $255,093.64 | — |
| 33 | 2029 | $135,107.15 | $267,848.32 | — |
| 34 | 2030 | $147,998.78 | $281,240.73 | — |
| 35 | 2031 | $161,535.00 | $295,302.77 | — |
| 36 | 2032 | $175,748.04 | $310,067.91 | — |
| 37 | 2033 | $190,671.73 | $325,571.31 | — |
| 38 | 2034 | $206,341.60 | $341,849.87 | — |
| 39 | 2035 | $222,794.96 | $358,942.36 | — |
What the number actually means
Coast FIRE is a threshold, not a finish line. Past it, the money you have already invested is enough to grow into your retirement target by itself. You still have to pay your rent and your groceries between now and then — but you no longer have to keep feeding the investments for the plan to work.
That makes it a genuinely different question from "when can I retire", and an easier one to answer, because it depends on far fewer guesses.
The arithmetic
It is the compound interest formula, used twice.
target = yearly spending ÷ withdrawal rate
coast number = target ÷ (1 + real return)years
The first line turns a spending figure into a pot. At a 4% withdrawal rate you need 25 times your annual spending; at 3.5% you need about 28.6 times. That multiplier is simply 1 ÷ the rate.
The second line runs compounding backwards. If $1,000,000 is the target and money grows at 5% a year for 30 years, then 1.0530 = 4.3219, so you need $1,000,000 ÷ 4.3219 = $231,377.45 today. Leave that alone for thirty years and it becomes the million.
Why the monthly rate is not the annual rate divided by twelve
This is the one piece of arithmetic here that is commonly got wrong, and it matters more the longer the projection runs.
Our debt payoff calculator divides the annual rate by twelve, because that is genuinely how lenders quote an APR and how a card statement computes a month's charge.
An investment return does not work that way. A stated 7% annual return means the money grows 7% over the year, compounding as it goes. The monthly rate is therefore the one that compounds to 7% in twelve steps —(1.07)1/12 − 1 = 0.5654% — not 7 ÷ 12 = 0.5833%.
The gap looks trivial. Over thirty years it is not: the nominal division overstates the final balance by several percent, and always in the flattering direction. We use the effective rate.
Everything is in today's money
The return you enter is a real return — after inflation. If you expect 8% nominal and 3% inflation, enter 5%.
This is deliberate. A projection in future dollars produces a bigger, more exciting number that buys less than it appears to, and it forces you to guess inflation on top of guessing returns. Working in today's money means the figure on screen means what it would mean if you spent it this afternoon, and removes one guess from a calculation that already has plenty.
What this deliberately does not do
A smooth curve is the most misleading thing about every projection of this kind, including this one. Four things it does not know:
- The order returns arrive in. A constant 5% and a real market averaging 5% are not the same experience. A bad run early does far more damage than the same run late — sequence-of-returns risk — and no constant-rate model can show it.
- Fees. Platform and fund charges come straight off your real return. Subtract them from the rate you enter.
- Tax. Which account the money sits in changes what you keep. We do not model tax anywhere on this site, deliberately — see how we verify our numbers for why.
- Other income. A state or workplace pension arriving later reduces what this pot has to cover, and would lower your target.
Use it to compare scenarios — what happens if I save $200 more, retire two years later, or assume a percentage point less growth. That comparison is robust. The single headline figure is not a prediction.
How we check this is right
The engine is tested against the compound interest formula, which anyone can reproduce on a pocket calculator. $100,000 growing at 7% for 30 years is $100,000 × 1.0730 = $761,225.50. Our projection walks 360 monthly steps at the effective rate and lands within 42 cents of that — about five parts in a billion, the accumulated cost of rounding to the cent every month.
There is a second check that ties the two halves together. Someone starting with exactly their coast number and contributing nothing must land exactly on their target thirty years later. Ours lands on $1,000,000.12 — twelve cents high, and high rather than low, which is the safe direction. The discount and the projection are genuine inverses.
Both assertions are exact rather than tolerance-based, so a change to the rounding policy has to be noticed and justified. The tests are public —read the methodology.
Common questions
- What is Coast FIRE, exactly?
- It is the point at which what you have already invested will grow, on its own, to your retirement target — so further saving becomes optional rather than necessary. It is not retirement. You still need to cover your living costs until then; you just no longer need to add to the investments.
- Why does it ask for a real return rather than a normal one?
- Because everything here is in today’s money. If you enter 5% and mean 5% after inflation, the projected balance means what it would mean if you spent it today. Entering a nominal return like 8% while thinking in today’s prices produces a number that looks large and buys less than you expect.
- Where does the withdrawal rate come from?
- It converts a spending figure into a target: at 4% you need 25 times your annual spending, at 3.5% you need about 28.6 times. The 4% convention comes from Bengen (1994) and the Trinity Study (1998), both of which tested historical US portfolios over 30-year windows. It is a widely used starting point, it is actively debated, and it is your input here rather than our recommendation.
- Should I trust a projection that assumes a constant return?
- Not as a forecast. Real returns arrive in an uneven order, and a bad run early in retirement does more damage than the same run later — sequence-of-returns risk, which a smooth curve hides completely. This tool describes what a constant rate would produce. It is a way to compare scenarios, not a prediction of yours.
- Does it account for tax, fees, or a pension?
- No. It models one pot growing at one rate. Platform fees and fund charges reduce your real return, so subtract them from the rate you enter. State or workplace pensions arriving later reduce what the pot has to cover, which this does not model. Both push the honest answer around, and neither is something a calculator can know about you.
Sources
- Bengen, W. (1994) — Determining Withdrawal Rates Using Historical Data — retrieved 2026-08-07
- Trinity Study (Cooley, Hubbard & Walz, 1998) — Retirement Savings — retrieved 2026-08-07
- The projection is checked against the compound interest formula, FV = PV × (1 + r)n, which is independently derivable and quoted identically everywhere.
Written and maintained by Vikash Singh. Last verified 2026-08-07.