Coast FIRE asks one planning question: is the amount you have invested today already enough to grow into your retirement target by a chosen age, if you add nothing more? Enter your ages, invested assets, desired spending, and return, inflation and withdrawal assumptions. The answer rests on one fixed return, so it cannot show market risk.
With the calculator’s hypothetical example values, a 35-year-old with $200,000 invested, retiring at 65 on $60,000 a year in today’s dollars, gets a coast threshold of about $413,327. That is an arithmetic comparison, not a finding that stopping contributions is safe.
Coast FIRE scenario calculator
This calculator runs in your browser. This calculator’s code does not send, save, or track your entries. All dollar amounts are USD.
Optional example: Inputs start blank. Load example fills hypothetical figures without calculating. Examples are not current rates, quotes, or recommendations.
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Inputs start blank, and Load example fills in the hypothetical figures above. The calculator does not ask for an account login or send inputs to a financial institution. It is a deterministic model, not a personalized retirement plan.
What does each Coast FIRE input mean?
- Ages: enter whole-year current and assumed retirement ages. Equal ages create a zero-year horizon, so the threshold equals the retirement target.
- Invested assets: the balance you want this model to grow, as of today.
- Desired annual spending: enter it in today’s purchasing power, not an already-inflated future amount. Include only the spending you want this portfolio to cover. The tool does not subtract Social Security or a pension.
- Return, inflation and withdrawal assumptions: enter a nominal annual return after investment fees, an annual inflation rate and a withdrawal fraction, all as percentages. A 4 in the last field means 4%, not 0.04.
The target, threshold, current assets, gap and real projected assets all use today’s dollars. Separate cards show future nominal dollars. Do not compare a future nominal balance with a today-dollar target.
How is the Coast FIRE number calculated in today’s dollars?
First, the model turns the nominal return and inflation into a real return: (1 + nominal return) ÷ (1 + inflation) − 1, with rates as decimals. This is more exact than simply subtracting inflation.
Next, retirement target in today’s dollars = desired annual spending ÷ withdrawal fraction. Finally, coast threshold today = retirement target ÷ (1 + real return)years until retirement.
One definition note: SEC’s Investor.gov describes real return as what is earned after accounting for taxes and inflation. This calculator adjusts only for inflation, so its “real” rate is still before taxes.
The gap card is the larger of zero and threshold minus current assets. If assets exceed the threshold, the gap is zero and a separate card reports the arithmetic excess. Neither label is approval to reduce work or saving.
How does the hypothetical 30-year default example work?
Inputs. Age 35, retirement assumed at 65, $200,000 invested, $60,000 of desired annual spending, a 7% nominal return, 2.5% inflation and a 4% assumed withdrawal fraction. All values are hypothetical.
Formula. The target is $60,000 ÷ 0.04 = $1,500,000 in today’s dollars. The real return is (1.07 ÷ 1.025) − 1 = about 4.3902% per year. The horizon is 30 years.
Result. The coast threshold is $1,500,000 ÷ (1.07 ÷ 1.025)30 = $413,327.11 today. Against $200,000 currently invested, the arithmetic gap is $213,327.11 today.
What to check. With no further contributions or early withdrawals, the same fixed path projects $725,817.38 at 65 in today’s purchasing power. The future nominal balance is $1,522,451.01, and the nominal counterpart of the target is $3,146,351.37. Keep each figure in its own units.
What changes if the return is one point lower or higher?
The calculator moves the nominal return exactly one percentage point below and above the base, while holding inflation, withdrawal, spending, horizon and the zero-contribution rule fixed. It recalculates the real return for each row. These are illustrations, not probabilities.
| Scenario | Nominal return | Real return | Threshold today | Projected assets at 65, real | Gap today |
|---|---|---|---|---|---|
| Low | 6% | 3.4146% | $547,811.65 | $547,633.48 | $347,811.65 |
| Base | 7% | 4.3902% | $413,327.11 | $725,817.38 | $213,327.11 |
| High | 8% | 5.3659% | $312,676.01 | $959,459.61 | $112,676.01 |
Even the high-return row leaves a modeled gap at the current $200,000 balance. A return assumption is not a return promise. Investor.gov notes that inflation reduces purchasing power, and investments carry uncertainty and possible loss.
What does a shorter 10-year horizon look like?
Inputs. A hypothetical 50-year-old with $500,000 invested assumes retirement at 60, $40,000 of annual spending in today’s dollars, a 6% nominal return, 2% inflation and a 4% withdrawal fraction.
Formula and result. The real return is 1.06 ÷ 1.02 − 1 = about 3.9216%. The target is $40,000 ÷ 0.04 = $1,000,000. Over ten years the threshold is $680,680.12 today, so the gap against $500,000 is $180,680.12 today.
What to check. At the same constant returns and no new contributions, the assets project to $734,559.43 in today’s purchasing power, or $895,423.85 in future nominal dollars. The future nominal target is $1,218,994.42. A shorter horizon leaves much less room for compounding to close a gap.
How the calculator handles inputs and rounding
The supported horizon ends at 80 years. Zero desired spending produces a zero target, and zero invested assets produce zero projected assets. With retirement age equal to current age, the threshold equals the target regardless of return.
The nominal projection compounds today’s assets at the nominal return; the separate nominal target inflates today’s target. They are future-dollar counterparts, not extra assets.
The tool rejects unsupported rates, horizons and extreme outputs rather than showing an apparently precise answer. It does not give a “time to coast” date: on a zero-contribution path with one fixed return and retirement date, a present gap does not disappear merely by waiting.
When does a Coast FIRE calculator not fit your situation?
- You expect Social Security or a pension. The tool does not subtract either. The SSA says retirement benefits can start as early as 62, are reduced before full retirement age and increase if you delay up to 70, so claiming age changes how much the portfolio must cover. Get your own estimate from SSA.
- You want to know if withdrawals will last. The model stops at retirement. Poor returns early in retirement can force withdrawals from a smaller portfolio, a sequence risk a constant-return path cannot show.
- You treat 4% as a rule. FINRA says there is no one-size-fits-all withdrawal percentage and that expert opinion tends to cluster between 3% and 5%. Here the rate is only an input to the target formula.
- Taxes, health costs or irregular saving matter. Investment and withdrawal taxes, health and long-term care costs, changing spending, account access rules and irregular contributions are excluded.
For a different starting point, the monthly savings interest calculator models regular deposits, while the emergency fund calculator addresses near-term cash needs. Neither replaces a retirement withdrawal plan.
Quick decision checklist
- Enter desired spending in today’s dollars, not an inflated future amount.
- Use a nominal return after fees and rerun the result at lower returns.
- Compare today-dollar figures only with today-dollar figures.
- Check your Social Security estimate and any pension before sizing the target.
- Treat a zero gap as a model result, not a signal to stop saving.
Sources and calculation review
- SEC Investor.gov: Real Return, real returns account for taxes and inflation and are lower than nominal returns.
- SEC Investor.gov: What is Risk?, uncertainty and inflation’s effect on purchasing power.
- FINRA: Managing Your Retirement Portfolio, withdrawal percentages, inflation, taxes and other income sources.
- SSA: Retirement Age and Benefit Reduction, benefits from age 62, full retirement age and increases for delay up to 70.
Official-source passages checked September 28, 2026. The two examples and the sensitivity table were recalculated by script and in the calculator. This page is educational and does not recommend a retirement date, an investment return or a withdrawal rate.
Prepared with AI-assisted research, drafting, and calculation checks. Not independently reviewed by a human financial professional.
