What is Coast FIRE Calculator?
The Coast FIRE Calculator helps you determine when you can stop saving and let your investments grow.
When to Use This Calculator
- Deciding whether to downshift to a lower-stress or lower-pay job — check if your savings already support coasting to retirement.
- Evaluating a career break or sabbatical — understand how a pause in contributions affects your long-term retirement timeline.
- Planning around a fixed retirement-age target — see exactly how much you need saved today to coast to age 60, 62, or 65.
- Stress-testing your Coast FIRE plan against different market-return assumptions (5%, 7%, 9%).
- Comparing Coast FIRE against full FIRE to understand how much more you'd need to save for complete early retirement.
- Setting annual savings goals — if you're not yet at your Coast FIRE number, calculate how much to save each year to hit it.
Steps:
- Enter current savings and age.
- Input retirement age and expected return.
- View Coast FIRE number and timeline.
Use Cases
- Career planning
- Savings strategy
- Lifestyle design
Key Benefits
- Determine the exact savings balance needed to coast to retirement without further contributions
- Model different return assumptions to understand how market performance affects your timeline
- Compare Coast FIRE against full FIRE and traditional retirement planning scenarios
- Plan career transitions with confidence — know when you can downshift without jeopardizing retirement
Pro Tips
- Use a conservative 5-7% return assumption — historical market averages are ~7-10% nominal, but plan for the lower range
- Add a 10-20% buffer above your calculated Coast FIRE number to protect against market downturns
- Run the calculation at multiple retirement ages (55, 60, 65) to see how each affects your target
- Track your actual portfolio growth annually against the projection — adjust contributions if you're falling behind
Common Mistakes to Avoid
- Using an overly optimistic return assumption (10%+) that inflates your coast number unrealistically
- Ignoring inflation — nominal returns and expenses must be consistent (use real returns or nominal consistently)
- Not accounting for sequence-of-returns risk — a market crash early in your coast period can derail the plan
- Forgetting that healthcare costs before Medicare eligibility (age 65) can be a major expense gap
Key Terms Explained
- Coast FIRE Number: The investment balance that, without additional contributions, will grow to fund your retirement target.
- FIRE Number: Your retirement target, calculated as annual expenses divided by your withdrawal rate (typically 25x at 4%).
- Withdrawal Rate: The percentage of your portfolio you withdraw annually in retirement (4% is the standard rule).
- Real Return: Investment return adjusted for inflation — a 7% nominal return minus 2.5% inflation = 4.5% real return.
- Sequence-of-Returns Risk: The danger that poor market performance early in retirement (or coast period) permanently reduces your portfolio.
- Lean FIRE: A minimalist FIRE variant targeting $25K-$40K annual expenses, requiring a smaller FIRE number than traditional FIRE.
Related Concepts
- FIRE Calculator — models the full FIRE number and timeline with ongoing contributions for comparison.
- Retirement Calculator — traditional retirement planning with contribution schedules and Social Security integration.
- Asset Allocation Calculator — helps you choose the right investment mix to achieve your target return.
- DCA Calculator — models dollar-cost averaging contributions to build toward your Coast FIRE number.
- Investment Growth Calculator — projects portfolio growth under different return and contribution scenarios.
Example
With $100K at age 30, 7% return, and retirement at 60, your investments grow to ~$761K without additional contributions.
Interpreting Your Results
Your Coast FIRE number represents the minimum investment balance you need today to reach your retirement target without making any additional contributions. If your current savings exceed this number, you've achieved Coast FIRE and can choose to stop contributing (or reduce contributions) while still reaching your retirement goal.
The most important variable is your expected annual return. A 2-percentage-point difference in return assumption can change your Coast FIRE number by 30-50%. Use a conservative estimate (5-7%) rather than historical averages to build in a safety margin.
If you haven't reached your Coast FIRE number yet, the calculator shows how many years of continued saving you need at your current rate. This helps you set a concrete target date for when you can begin coasting.
Remember that Coast FIRE is a minimum threshold — any additional contributions beyond it will either accelerate your retirement timeline or increase your final retirement fund. It's a floor, not a ceiling.