Free tool
Coast FIRE Calculator
Find the amount you need invested today to coast to retirement, the age you get there, and what to invest each month to coast by the age you choose.
How to calculate your Coast FIRE number
Your Coast FIRE number is the amount you need invested today so that growth alone, with no new contributions, reaches your full FIRE number by your retirement age. The whole calculation is one formula:
Coast FIRE number = FIRE number ÷ (1 + real return)^years to retirement
The worked example below uses this page's default inputs: age 30, retiring at 65, $50,000 a year of spending, a 7% return, 2.5% inflation, and a 4% withdrawal rate. These are adjustable assumptions, not forecasts. Change any of them in the calculator above and every number updates.
1. Find your FIRE number
Divide the amount you expect to spend each year in retirement by your withdrawal rate.
FIRE number = Annual spending ÷ Withdrawal rate
Example: $50,000 ÷ 4% = $1,250,000.
2. Convert your expected return into a real return
Working in today's money keeps the FIRE number comparable to your spending now. Strip inflation out of the return you assume:
Real return = (1 + nominal return) ÷ (1 + inflation) − 1
Example: (1 + 0.07) ÷ (1 + 0.025) − 1 = 4.39%.
3. Discount the FIRE number back to today
Count the years until retirement and divide your FIRE number by the growth it gets over that time.
$1,250,000 ÷ (1 + 4.39%)^35 = $1,250,000 ÷ 4.50 = $277,852
With 35 years of growth ahead, $277,852 invested today is enough to coast to retirement under these assumptions.
4. Compare it with what you have
Starting from $25,000 and investing $800 a month, you do not reach your Coast FIRE number before retirement. Raise contributions or revisit your assumptions.
Coast FIRE number by the age you start coasting
The later you plan to stop saving, the smaller the number, because less growth is left to do the work. The last column is the monthly investment needed from $25,000 today to get there on time.
| Start coasting at | Years of growth left | Coast FIRE number | Monthly investing needed |
|---|---|---|---|
| 30 (today) | 35 | $277,852 | n/a |
| 35 | 30 | $344,439 | $4,682 |
| 40 | 25 | $426,985 | $2,592 |
| 45 | 20 | $529,312 | $1,905 |
| 50 | 15 | $656,162 | $1,570 |
| 55 | 10 | $813,413 | $1,375 |
| 60 | 5 | $1,008,348 | $1,249 |
How to use this calculator
- 1
Enter your age and target retirement age
Set the sliders for your current age and the age you want to retire. The gap is your runway.
- 2
Set your current portfolio and monthly contribution
Drag the balance and contribution sliders to match what you have invested today and what you're adding each month.
- 3
Tune the assumptions
Adjust expected return, inflation, and safe withdrawal rate. Defaults reflect a balanced equity portfolio.
- 4
Read your CoastFIRE number
The headline shows what you'd need invested today to coast to retirement with zero new contributions, plus how many years until you reach it at your current pace.
Frequently asked questions
- What is CoastFIRE?
- CoastFIRE is the point at which your invested portfolio is large enough that, without any new contributions, compound growth alone will carry it to your retirement number by your target retirement age. After hitting CoastFIRE you no longer need to save for retirement. You can spend what you earn, as long as your portfolio keeps growing.
- What is the Coast FIRE formula?
- Coast FIRE number = FIRE number ÷ (1 + real return)^years to retirement. Your FIRE number is your annual retirement spending divided by your withdrawal rate (for example, spending × 25 at a 4% rate). The real return is your expected return with inflation removed: (1 + nominal) ÷ (1 + inflation) − 1.
- How do I calculate my Coast FIRE number?
- Start with your annual expenses in retirement, subtract any public pension income you expect, and divide by your safe withdrawal rate to get the portfolio you need at retirement. Then discount that target back to today using your real (inflation-adjusted) expected return over the years until you retire. The result is the amount you would need invested today to coast to retirement with zero new contributions.
- How much do I need to invest each month to reach Coast FIRE by a certain age?
- Use the "Plan your coast date" panel under the chart. Pick the age you want to stop saving and the calculator works backwards to the level monthly investment that grows your current portfolio to your Coast FIRE number at that age. After that age, the projection assumes no more retirement contributions are needed.
- What return rate should I use?
- The calculator defaults to a 7% nominal return and 2.5% inflation, which works out to a real return of about 4.4%. These are starting assumptions you can change, not predictions. The sensitivity table under the chart shows how your Coast FIRE number moves if returns come in one or two points higher or lower, so test a few scenarios before relying on one.
- Is the 4% safe withdrawal rate still valid?
- The 4% rule comes from research on historical 30-year retirements, most often cited as the Trinity Study. Longer retirements, different portfolios, or different market conditions can justify a lower or higher rate. Treat 4% as an adjustable assumption and use the withdrawal rate slider to see how your number changes.
- Does this account for taxes or fees?
- Not directly. The projection is a pre-tax model in today's money. Withdrawals can be taxed depending on the account, and investment fees reduce your growth every year. To include fees, lower the expected return by your total annual fee (for example, 7% minus 0.2% in fees means entering 6.8%). Treat the result as an optimistic ceiling and stress-test it.
- Are my inputs saved?
- Yes. The calculator stores your last inputs in your browser's local storage, so they'll be there next time you visit. You can also copy a shareable link that encodes your inputs in the URL. The URL takes precedence over saved values when opened.