Calculation Guide
How Much Do You Need to Coast FIRE?
The amount you need to Coast FIRE is a present-value estimate tied to your own future spending target, time horizon, and planning assumptions.
Mason ReedEditorial contributor
Quick answer
What this article explains
How much you need to Coast FIRE depends on the retirement spending you want to support, the withdrawal-rate assumption you choose, the years until retirement, and the real growth assumption. It is not a fixed percentage of income or a universal dollar figure.
Start with retirement spending
A common planning approach begins with annual retirement spending in today’s dollars. Dividing that amount by a withdrawal-rate assumption produces a hypothetical future portfolio target; the withdrawal rate is an assumption, not a guarantee of sustainability.
A spending target should account for the lifestyle you are trying to support and should be revisited when housing, healthcare, family, or work plans change.
Bring the target back to today
The Coast FIRE number discounts the estimated target by an assumed inflation-adjusted growth rate over the years until retirement. With more time or a higher real-return assumption, the calculated present amount is lower; with less time or lower growth, it is higher.
This relationship explains why two people with the same retirement spending can arrive at different Coast FIRE numbers.
Test the assumptions before treating the number as a goal
Use multiple reasonable input sets in a Coast FIRE Calculator. A range can be more useful than one precise-looking number because no simple model captures every investment, tax, employment, or personal risk.
- Compare at least one less favorable return or inflation assumption.
- Consider whether expected retirement spending includes known recurring costs.
- Keep room for changes in plans rather than relying on a single result forever.
Try the Coast FIRE Calculator
Compare your own retirement spending, timeline, savings, return, and inflation assumptions in a private browser-based estimate.
Common questions
Is my Coast FIRE number the same as my full retirement number?
No. The Coast FIRE number is a present amount estimated to grow toward a future target under chosen assumptions.
Can I use a lower spending target to reach Coast FIRE sooner?
A lower spending assumption changes the calculation, but it should reflect a lifestyle you would genuinely be comfortable sustaining.
Sources and further reading
These links provide general background. They do not validate any individual projection or replace professional advice.
