Coast FIRE: When Can You Stop Saving for Retirement?

Coast FIRE is the point where your existing investments are projected to reach your retirement target without further contributions. You still need to cover living costs until then, and the answer depends on future returns, spending and your retirement date.

That can make a lower-paid job worth considering long before you can stop working. But crossing the coast number once does not settle retirement forever. The target changes as you age, and markets can move you back below it.

To judge whether you can reduce contributions, compare your portfolio with what it needs to grow into by retirement. A rising balance alone does not tell you whether you are closer.

The arithmetic

The whole calculation is one division. Take your FIRE number and discount it back to today at your expected real return over the years remaining until retirement:

fi_number      = annual_spending / withdrawal_rate
growth_multiple = (1 + real_return) ^ years_to_retirement
coast_number   = fi_number / growth_multiple

Everything here is in today's dollars at a real return, meaning a return after inflation. Use a return after investment fees too: fees reduce the money left to compound. The model assumes unchanged purchasing-power spending and no withdrawals before retirement.

For an illustrative household planning on $60,000 of annual retirement spending, a 4% withdrawal assumption gives a $1.5 million target. At an assumed 5% real return over 25 years, the growth multiple is 1.05^25, approximately 3.386. The coast number is $1,500,000 ÷ 1.05^25 = $442,954, about 30% of the full target.

Neither rate is a promise. The withdrawal-rate guide explains why 4% cannot establish safety for every portfolio and retirement length.

Here is the same $1.5M target, seen from different ages, retiring at 60 with a 5% real return:

Age	Years to 60	Coast number	Multiple of $60k spending
35	25	$442,954	7.4x
40	20	$565,334	9.4x
45	15	$721,526	12x
50	10	$920,870	15.3x
55	5	$1,175,289	19.6x
60	0	$1,500,000	25x

Time does much of the work in the first row. By age 55, only five years remain, so the portfolio must already contain most of the target. There is no universal halfway milestone.

Why the coast number rises every year

With a fixed retirement date, spending target and positive assumed return, the coast number rises each year because there is less runway left. At 5%, it rises by 5%, exactly matching a portfolio that earns the modeled return.

So a portfolio at 70% of its coast number stays at 70% if it grows at that same rate with no contributions or withdrawals. The dollar balance rises, but the funding gap does not close in percentage terms.

Waiting alone does not repair a shortfall in this model. Contributions, lower planned spending or a later retirement date can change the answer. Actual returns above or below the assumption also change your position. The constant funded percentage is an identity inside the smooth-return model, not a rule governing markets.

Worked example: 35, coasting to 60

Keep the same illustrative assumptions and suppose this 35-year-old has $520,000 invested. That is $77,046 above the coast number, or 117.4% funded. Under the model:

• Stopping contributions projects $520,000 × 1.05^25 = $1,760,905 at 60, a $260,905 surplus over the target.
• Keeping $18,000 a year going, added at each year end, clears that same $1.5 million target at 51. This does not establish retirement readiness at 51; a longer retirement needs a separate withdrawal plan.

The surplus measures room inside these assumptions. It is not a safety rating. Drop the assumed real return from 5% to 4%, and the coast number becomes $562,675. The same $520,000 portfolio is now about $42,675 short. Without contributions, it projects to roughly $1.386 million at 60.

Real markets also fluctuate. The SEC's investment guide explains the risk of losing principal and why allocation should reflect your horizon and risk tolerance. This calculation supplies no probability that your chosen return will occur.

What crossing the line can buy

If a lower-paid job covers current costs, reducing retirement contributions could help the switch fit your budget. But $60,000 of spending does not mean a $60,000 gross salary is enough. Taxes, health coverage, other savings goals and irregular bills still need funding. Current costs can also differ from your retirement budget.

An unpaid year requires its own funding. Withdrawing from the investments counted toward coasting reduces the balance left to grow; the original calculation no longer applies. Keep emergency and career-break money outside that invested balance if it will be spent along the way.

Use the Coast FIRE Calculator to compare your invested balance with today's target, project contribution crossings and test lower-return or later-retirement assumptions. Its figures are in today's dollars; it does not model taxes, benefit schedules or market volatility. Include expected retirement taxes and health costs in spending, without treating account balances as equally spendable after tax.

Before reducing contributions, check whether the plan still works at a lower return and whether the proposed job covers your actual cash needs. Those two checks give the coast milestone a practical meaning: more choice about how much to save, with a plan for the years before retirement.

This is an explanation of planning arithmetic, not personalised financial advice. Your situation, tax treatment, and risk tolerance are yours.