Coast FIRE (Part-Time Income) Calculator
Check whether your invested savings can coast to retirement on their own once part-time work covers part of your future spending.
How it works
Net spending = expenses − part-time income · FIRE number = net spending ÷ withdrawal rate · Coast today = FIRE number ÷ (1 + r)^years · Projected = invested × (1 + r)^years
Coast FIRE means your invested assets are already large enough to grow into your full retirement target without a single further contribution — you only need to cover current living costs until then. Adding part-time income in retirement shrinks the nest egg you must reach, because you are withdrawing from the portfolio for a smaller slice of your spending. The calculator discounts that smaller target back to today to show the balance you would need right now to coast.
Worked example
A 35-year-old with $150,000 invested, $45,000 of expenses, and $15,000 of part-time income at a 4% withdrawal rate needs $30,000 ÷ 4% = $750,000. At 7% over 25 years, $150,000 grows to about $814,000 — above the target, so they have already hit Coast FIRE.
Frequently asked questions
What is Coast FIRE?
It is the point where your existing investments will compound into your retirement number on their own, so you no longer need to save — you just need to earn enough to pay today’s bills until retirement.
How does part-time income change the math?
Every dollar of ongoing income in retirement is a dollar you do not withdraw. That lowers the portfolio you must accumulate: at a 4% rule, $15,000 of income replaces $375,000 of nest egg.
Is 4% a safe withdrawal rate for early retirees?
The 4% rule was derived for a 30-year horizon. Retiring earlier lengthens the horizon, so many early retirees use 3–3.5% or plan flexible spending to be safe.
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Educational estimate, not financial advice. Investment returns are not guaranteed.