Coast FIRE is a conditional projection of the portfolio needed today to fund retirement under your entered assumptions. It does not establish that retirement is secured or that reducing work is affordable.
What Coast FIRE Actually Means
Coast FIRE describes a modeled balance, not a promise about future investment performance. The calculator first subtracts retirement income active at the chosen retirement age from annual retirement spending, flooring the portfolio-funded gap at zero. Dividing that gap by the entered withdrawal-rate assumption gives the retirement target. Discounting that target using the Fisher real return gives the balance required today. A balance above that threshold is labeled coast now under these assumptions, even when the real return is zero or negative. A balance below it requires additional contributions, a different horizon or different assumptions.
The selected stop-saving age determines the contributing stage. Required monthly contributions occur at the beginning of each month in today’s purchasing power, then stop during the coasting stage. Their nominal dollar amount rises with the entered inflation rate. Selecting no contributing time while below target produces a named not-reached result rather than free retirement funding. Review the annual ledger alongside the chart, and revisit return, spending, income and withdrawal assumptions before changing a personal plan.
How the Coast FIRE Calculation Works
The calculation has two steps. First, determine your FIRE number: divide your expected annual retirement spending by the safe withdrawal rate you choose. If you plan to spend $60,000 per year and model a 4% rate, the gross FIRE number is $1,500,000. If other income will cover part of that spending, the calculator subtracts that income before calculating the portfolio-funded Coast FIRE target. Second, discount the portfolio target back to today's dollars using the real rate of return — (1 + nominal return) / (1 + inflation) − 1. For example, a 7% nominal return and 3% inflation produce a 3.88% real return; with 28 years until retirement, $1,500,000 / (1.0388)^28 is approximately $516,000. Every result depends on the assumptions, so compare several return, inflation, spending, and withdrawal-rate scenarios rather than relying on one projection.
The Role of the Safe Withdrawal Rate
Your safe withdrawal rate (SWR) is the percentage of your retirement portfolio you plan to withdraw in the first year. The calculator applies that percentage to the portfolio-funded spending target; lowering the rate increases the required FIRE and Coast FIRE amounts. Historical studies can provide context, but they do not guarantee future results, and a withdrawal plan may need to account for taxes, fees, changing spending, market volatility, and the length of retirement. Compare multiple SWR assumptions and consider professional advice for a personal plan.
Life After Coast FIRE
Reaching a modeled Coast FIRE balance does not pay current living costs. The optional coast-job figure is annual take-home income, compared with current annual living costs and any required retirement saving. If current costs are blank, the calculator uses the entered annual retirement spending as an explicit budget illustration. For example, $25,000 of take-home work income against $50,000 of current costs leaves a $25,000 annual living gap before any additional saving. Future pension or other retirement income does not fill that current gap.
An income start age applies only to the retirement target: income starting after the modeled retirement date is excluded, because the projection ends at retirement and does not model a later withdrawal bridge. Compare reviewed presets while retaining custom assumptions, or select a sensitivity cell to preview a different spending and return combination. These previews do not change the current plan. Read real and nominal balances separately, review the contribution stop age, and treat every result as an illustration rather than a guarantee.