A Coast FIRE number is the amount invested today that could grow to a future portfolio target without additional contributions. When annual spending is stated in today’s dollars, use an estimated return after inflation. Divide the future target by one plus the real return raised to the number of years until retirement.
Coast FIRE discussions often turn on three practical questions: whether to use a return before or after inflation, whether future contributions still count, and how much confidence to place in a smooth-growth estimate. The forum source records that reader problem. The calculations here are original hypothetical examples.
Start here: a practical action plan
- Write annual retirement spending in today’s dollars.
- Calculate the spending-based target with a documented withdrawal assumption.
- Run the Coast FIRE estimate at three real returns and at more than one retirement age.
- Keep future contributions as a separate scenario so the coast estimate remains understandable.
- Using a nominal return with a target stated in today’s dollars.
- Counting emergency cash or home equity assigned to another job.
- Treating one smooth-return result as proof that future contributions can safely stop.
Define what coasting means before calculating it
In this guide, Coast FIRE means the current invested balance could reach a chosen retirement target under a return and time assumption even if new retirement contributions stop. It does not mean current living expenses are covered. Income is still needed until the planned retirement date.
Continuing contributions after reaching the estimate creates a different scenario. That can add margin or move the date earlier, but it should not be hidden inside the number labeled Coast FIRE.
Age 35 to 60 with $60,000 of annual spending
Assume a person is 35, plans to retire at 60, expects $60,000 of annual spending in today’s dollars, uses a 4% withdrawal assumption, and tests a 5% annual real return. The spending-based future target is $60,000 divided by 0.04, or $1,500,000.
There are 25 years for the current balance to compound. Dividing $1,500,000 by 1.05 raised to the 25th power produces $442,954, rounded to the nearest dollar. Under those assumptions, that is the Coast FIRE estimate at age 35.
| Step | Calculation | Result |
|---|---|---|
| Future portfolio target | $60,000 divided by 4% | $1,500,000 |
| Years to retirement | Age 60 minus age 35 | 25 years |
| Growth factor | 1.05 raised to 25 | 3.3864 |
| Coast FIRE estimate | $1,500,000 divided by 3.3864 | $442,954 |
Keep today’s dollars and the return assumption consistent
A nominal return includes inflation. A real return is the growth left after inflation. If spending is entered in today’s purchasing power, a real return keeps the units consistent. One way to convert is: real return equals one plus the nominal return, divided by one plus inflation, minus one.
For example, a 7% nominal return and 2.5% inflation produce about 4.39% real growth: 1.07 divided by 1.025, minus 1. Simply subtracting gives 4.5%, which is close but not exact. Both numbers remain assumptions, not forecasts.
The return assumption can move the result by hundreds of thousands
Keep the $1.5 million target and 25-year timeframe, then change only the real return. At 3%, the estimate is $716,408. At 5%, it is $442,954. At 7%, it is $276,374. A more optimistic return makes today’s required balance look much smaller.
Use a range instead of treating one result as a pass or fail line. A constant return also hides volatility and the order of annual gains and losses.
| Estimated real return | Coast FIRE estimate today | Difference from 5% case |
|---|---|---|
| 3% | $716,408 | +$273,454 |
| 5% | $442,954 | Baseline |
| 7% | $276,374 | -$166,580 |
Count only assets assigned to the retirement target
Include invested assets that are part of the retirement plan. Do not count an emergency fund, a home you intend to keep, money reserved for tuition, or the same balance assigned to another goal.
Account access and taxes matter even when an account belongs in the long-term total. The IRS explains that a 10% additional tax generally applies to early IRA or retirement-plan withdrawals unless an exception applies. A Coast FIRE estimate says nothing about how money will be accessed or taxed.
- Calculate annual retirement spending in today’s dollars.
- Choose and document a withdrawal-rate assumption.
- Use a range of real returns and retirement ages.
- Review the result after major spending, balance, or timeline changes.
Frequently asked questions
What is the formula for Coast FIRE?
First divide annual spending by the withdrawal rate to estimate the future portfolio target. Then divide that target by one plus the estimated real return raised to the years until retirement.
Should a Coast FIRE calculator use a real or nominal return?
Use a real return when spending and the future target are in today’s dollars. Use a nominal return only when the future target has also been increased for inflation. Mixing the two units can materially distort the result.
Do future contributions count in Coast FIRE?
A strict Coast FIRE estimate assumes no future retirement contributions. You can model continued contributions as a separate scenario for added margin or an earlier date.
Does Coast FIRE mean I can stop working?
No. The estimate addresses a future retirement portfolio. Current living costs still need income until the planned retirement date unless another source covers them.
Which accounts count toward Coast FIRE?
Count invested assets assigned to retirement, subject to your tax and access plan. Do not count emergency cash, home equity you plan to keep, or balances already assigned to another goal.
How often should I recalculate Coast FIRE?
Recalculate after a major balance change, a new spending estimate, a different retirement age, or a changed return assumption. An annual review is also useful because the result is sensitive to both time and market value.
Sources and review notes
The calculations and scenarios in this guide are original BreadWinnr worked examples. We recalculated each example and checked that its parts match the stated total. Official sources support the financial concepts. Forum links document the reader problem that prompted the guide and are not treated as financial authority.
- Investor.gov: Compound Interest Calculator
- IRS: Hardships, early withdrawals, and loans
- William Bengen: The 4% Rule and its assumptions
- Forum question: Coast FIRE, burnout, and a 5% real-return assumption
Read our research, testing, corrections, and source policy.
This guide provides general financial education. It does not account for your complete financial, tax, legal, or contractual situation.
Make the example yours.
Use the coast fire calculator to try a different starting point.