Planning Guide
How to Calculate Your Coast FIRE Number
A clear, input-by-input explanation of what the Coast FIRE Calculator estimates and why each assumption changes the result.
Miles CarterEditorial contributor
Quick answer
What this article explains
To calculate a Coast FIRE number, first estimate the retirement portfolio target from annual spending and a withdrawal-rate assumption. Then discount that target by the years to retirement using an inflation-adjusted return assumption.
Start with a retirement portfolio target
The calculator estimates a target portfolio by dividing annual retirement spending in today’s dollars by a chosen safe withdrawal rate. For example, a $30,000 spending assumption and a 4% withdrawal-rate assumption produce a $750,000 target before any growth assumption is applied.
This is a planning convention, not a claim that one withdrawal rate is safe for every household or market environment.
Adjust for time and inflation
FireCalcTools uses expected annual return minus inflation to estimate a simple inflation-adjusted annual return. It then asks how much of the future retirement target would need to be invested today to grow over the remaining years.
A longer timeline or higher assumed real return generally lowers the amount needed today, while a shorter timeline or lower real return generally raises it.
Compare the result with your current plan
Current invested assets are compared with the estimated Coast FIRE number. The projection also models monthly contributions through the retirement age so you can see whether the plan reaches the annual Coast FIRE milestone.
- Include investment assets intended for retirement, not everyday checking or emergency cash.
- Enter spending in today’s dollars so the inputs use the same purchasing-power basis.
- Treat the output as a scenario to revisit when your circumstances or assumptions change.
Try the Coast FIRE Calculator
Compare your own retirement spending, timeline, savings, return, and inflation assumptions in a private browser-based estimate.
Common questions
Why is my Coast FIRE number lower than my retirement target?
The Coast FIRE number is the present amount estimated to grow to the retirement target over time.
Should I use nominal or real return?
This calculator asks for nominal return and inflation separately, then uses their simple difference for its inflation-adjusted assumption.
Sources and further reading
These links provide general background. They do not validate any individual projection or replace professional advice.
