Coast FIRE: Required Portfolio at Age 30, 35 and 40

Coast FIRE Portfolio Targets

Coast FIRE describes a point where your invested assets are projected to grow to a chosen retirement goal with little or no additional saving. The “required portfolio” at age 30, 35, or 40 depends on your retirement age, expected returns, inflation, taxes, and whether you plan to stop contributions entirely. People often treat Coast FIRE like a single number, then discover their inputs were doing most of the work. A practical approach starts with a retirement target and works backward to the portfolio size that makes the remaining path plausible.

In many Coast FIRE discussions, the portfolio target is framed as the amount you need at a given age so that future growth covers the gap between your retirement goal and what you will still contribute. For example, if you plan to retire at 60 and stop saving at 35, the “required portfolio at 35” is the balance that, under your assumptions, grows enough from 35 to 60. The same logic applies at 30 or 40, but the time horizon changes the required starting balance. Shorter time horizons generally require larger balances, and longer horizons generally require smaller ones.

Because returns are uncertain, Coast FIRE targets should be treated as scenario estimates, not guarantees. A model that assumes a steady average return can look fine on paper and still fail in a bad sequence of returns. That risk becomes more relevant when you plan to reduce contributions, since you lose the ability to “buy back” losses with new savings. If you want a number you can act on, you need a method that includes downside scenarios and a clear definition of your retirement spending goal.

Common Coast FIRE Mistakes

The first mistake is mixing up “portfolio that reaches retirement” with “portfolio that reaches retirement plus spending.” A retirement plan needs a spending plan, not just an account balance. If you choose a retirement goal without translating it into annual spending, you can end up with a target that is too low or too high. Another frequent error is using nominal returns without accounting for inflation, which inflates the apparent progress.

The second mistake is assuming the same return every year. Market returns vary, and the order of returns matters, especially when you stop contributing and start relying on growth. A sequence where markets fall early in the Coast phase can reduce the ending balance even if the long-run average return matches your assumption. This is why many planners run multiple scenarios, such as a “base case” and a “downside case” with lower returns and higher volatility.

The third mistake is ignoring taxes and account location. If part of your portfolio sits in taxable brokerage accounts, dividends and capital gains can change the effective growth rate. If you use tax-advantaged accounts, withdrawal rules and tax brackets affect net spending. Even a simple model can incorporate a rough tax drag, but readers often skip it and then wonder why the results feel optimistic.

The fourth mistake is treating “required portfolio” as a single fixed figure across ages. The required balance at 30, 35, and 40 changes because the time available for compounding changes. It also changes because your retirement age and stopping age change the number of years you contribute. If you stop contributions at 40, you have fewer years for growth, so the required portfolio at 40 is typically larger than at 35. If you stop at 30, the required portfolio at 30 is typically smaller than at 35, but the plan still depends on the same assumptions.

Supporting technologies for this planning are mostly spreadsheet-based modeling and retirement calculators that let you set assumptions. A common practical tool is a retirement projection spreadsheet with inputs for contribution schedule, expected return, inflation, and taxes. If you use a calculator, check whether it models inflation-adjusted spending and whether it supports multiple scenarios. I’ve seen people copy a single output number from a calculator and never revisit the assumptions; the model becomes a black box, and the number stops being actionable.

How To Estimate Required Amounts

Step 1: Define Retirement Spending

Start with the annual amount you want to spend at retirement, then adjust for inflation. If you target $60,000 per year in today’s dollars, your model should treat that as inflation-adjusted spending rather than a fixed nominal amount. Add categories that match your situation, such as housing, healthcare, and travel, and subtract expected income sources like Social Security if you plan to include them. A cautious model uses conservative spending assumptions because spending often rises early in retirement for travel and healthcare transitions.

For a quick sanity check, translate spending into a “real” retirement goal. Many planners approximate the retirement portfolio needed by dividing real annual spending by a sustainable withdrawal rate, then stress-testing. Even if you don’t use a withdrawal-rate method, you still need a retirement balance target that corresponds to your spending plan. If you’re unsure about healthcare costs, use a range and run the model twice; one run with a lower healthcare assumption and one with a higher one.

Step 2: Choose Assumptions You Can Defend

Pick an expected real return (after inflation) and a downside scenario. Real returns are easier to reason about because your spending target is in today’s dollars. A base-case real return might be around 3% to 5% depending on asset mix, but you should not treat any single number as “the” truth. For the downside case, reduce the real return and consider a lower ending balance even if averages look acceptable.

Account for taxes with a simple tax drag if you cannot model taxes precisely. For example, if you hold mostly in a taxable brokerage, dividends and capital gains can reduce effective growth relative to a tax-advantaged account. If you hold mostly in retirement accounts, withdrawal taxes depend on your tax bracket and the account type. A practical aside: if you’re using a spreadsheet, label each assumption cell clearly and version it; I’ve seen models get edited in March 2026 and then reused without remembering which return assumption changed.

Step 3: Solve Backward From Your Stop Age

Once you set a retirement balance target and a stopping age, you can solve for the portfolio size needed at that age. The core idea is that your current portfolio grows from the stop age to retirement, and that growth must cover the remaining gap. If you stop contributions at 30, the required portfolio at 30 is smaller than if you stop at 40, because you have more years of compounding. If you keep contributing until 35, the required portfolio at 35 is smaller than if you stop at 35.

In spreadsheet terms, you can model the future value of your portfolio at retirement under your chosen real return and then work backward to the present value at the stop age. If you prefer a calculator, choose one that supports inflation-adjusted projections and multiple scenarios. If the tool only outputs a single projection without scenario testing, you may need to adjust assumptions manually and rerun the calculation.

Step 4: Stress-Test With Sequence Risk

Sequence risk is the risk that poor returns happen early in the Coast phase. A simple average-return model can miss this. A more cautious approach runs at least two scenarios: one base case and one downside case with lower returns and a longer period of weakness. If you want more realism, use a Monte Carlo simulation tool that models return variability and sequences, but still interpret results carefully.

Also stress-test your plan for spending changes. If your retirement spending rises by 10% due to healthcare or housing, the required portfolio increases. If you plan to reduce work but not stop entirely, you can treat part-time income as a buffer that lowers the required portfolio. People often forget that Coast FIRE is not always “zero contributions”; some readers keep small contributions or earn part-time income, which changes the math.

Educational Examples With Numbers

Example 1 (Stop at 30): Assume a reader wants retirement spending of $70,000 per year in today’s dollars at age 60. They estimate a retirement portfolio target using a sustainable withdrawal approach and then run a backward calculation for the portfolio needed at age 30 if contributions stop at 30. Using a base-case real return assumption and a downside scenario, the required portfolio at 30 comes out lower than the required portfolio at 35 or 40 because the portfolio has more years to compound. The exact number depends on the retirement target method and the return assumptions, so the reader should treat the output as a range rather than a single figure.

Example 2 (Stop at 40): Another reader targets the same retirement spending at age 60 but plans to stop contributions at 40. Their required portfolio at 40 is higher because there are fewer years for growth. If they use the same base-case real return as in Example 1, the required balance at 40 might look manageable, but the downside scenario can push the required balance materially higher. This example shows why readers should not compare “required portfolio” numbers across ages without matching retirement age, stopping age, and spending assumptions.

These examples are educational and omit personal details like current balances, contribution amounts, and account types. In practice, you should plug in your own spending target, retirement age, and account mix. If you share your assumptions with a planner, ask them to show the downside scenario and the tax treatment, not just the base-case output.

Coast FIRE Checklist And Table

The table below compares how the required portfolio typically shifts with stopping age under the same retirement goal and return assumptions. It is a directional guide, not a universal rule, because taxes, spending, and return assumptions can change the outcome.

Use this step-by-step checklist to compute your own required portfolio at each age. If any step feels uncertain, rerun the model with a range and keep the spreadsheet versioned.

1. Pick retirement age and define retirement spending in today’s dollars.
2. Choose an asset allocation for the Coast phase and estimate a real return range.
3. Set a stopping age (30, 35, or 40) and decide whether contributions truly stop.
4. Model taxes using account types and a simple tax drag if needed.
5. Run at least two scenarios: base case and downside case with lower real returns.
6. Check feasibility by comparing the required portfolio to your current balance and realistic contribution capacity.
7. Document assumptions so you can update the model when markets or spending change.

Common Mistakes That Undermine Trust

Some readers copy a “required portfolio” number from a blog post without matching assumptions. If that number used a different retirement age, different spending level, or a different return assumption, the output becomes misleading. A trustworthy calculation shows the assumptions and the scenario range, not just a single figure.

Another mistake is ignoring account location and withdrawal rules. Readers sometimes assume tax-advantaged accounts grow the same as taxable accounts, then discover the effective growth rate differs. If you plan to withdraw from retirement accounts, withdrawal taxes and required minimum distributions can change the net spending path. Even if you do not model every detail, you should at least separate taxable and tax-advantaged balances.

People also overfit the plan to a single market outcome. If you run a model with a return assumption that matches a recent period, the required portfolio can look smaller than it should. A mild frustration here is that many calculators default to optimistic assumptions; you need to check the default settings and change them to match your risk tolerance. If you use a tool like a retirement projection spreadsheet, record the version of your assumptions (for example, “v1.3 return range”) so you can trace changes later.

Finally, readers sometimes treat Coast FIRE as a one-time decision. In reality, you may adjust contributions, spending, or retirement age as your situation changes. A plan that includes a “re-check date” after major life events tends to stay grounded. Without that, the model can drift away from reality.

FAQ

What Does “Required Portfolio” Mean?

It is the account balance at a chosen age that, under your assumptions, is projected to grow to a retirement goal by your retirement age with little or no additional saving.

How Do I Estimate Coast FIRE At 30?

Set your retirement spending target in today’s dollars, choose a real return range for your asset mix, decide whether contributions stop at 30, then solve backward for the portfolio size that meets the retirement goal in base and downside scenarios.

Why Do Required Amounts Rise At 35 And 40?

Stopping contributions later shortens the compounding period and increases reliance on market growth during fewer years, so the portfolio needed at 35 or 40 typically exceeds the portfolio needed at 30 for the same retirement goal.

Do Taxes Change Coast FIRE Calculations?

Yes. Taxes can reduce net returns in taxable accounts and affect withdrawal taxes later, so the effective growth rate and the net spending path can differ from a tax-free model.

Is Coast FIRE A Guarantee?

No. It is a scenario-based projection that can fail under poor return sequences, higher-than-expected spending, or changes in taxes and account access.

Author's Insight

Coast FIRE is best treated as a modeling framework rather than a fixed rule. The “required portfolio” at ages 30, 35, and 40 is highly sensitive to real return assumptions, inflation treatment, and taxes, so a single number without scenario testing often misleads. A cautious workflow uses a retirement spending target in today’s dollars, runs base and downside cases, and documents assumptions in a versioned spreadsheet. If you want to reduce uncertainty, you can also model partial work income or continued small contributions, since those change the required portfolio materially.

Key Takeaways

• Required Coast FIRE portfolio sizes at 30, 35, and 40 depend on retirement age, spending in today’s dollars, real return assumptions, and taxes.
• Stopping contributions earlier usually lowers the required portfolio because compounding has more time, but sequence risk still matters.
• Use at least two scenarios (base and downside) and avoid relying on a single optimistic output.
• Account type and withdrawal taxes can shift results, so separate taxable and tax-advantaged balances in your model.
• Re-check your plan after major life changes and when your assumptions stop matching reality.