Coast FIRE is when your investments are big enough that, without adding another dollar, they'll grow into your retirement number on time. From then on, work only has to pay your current bills.
How it's calculated
FIRE number F = spending ÷ withdrawal rate Coast number = F ÷ (1 + r)years to retirement
The Coast number is the present value of your FIRE number at the real return r. If you have at least that much invested, you've hit Coast FIRE.
Your Coast age is when your investments, plus the yearly saving you enter, first reach the Coast number for that age. With yearly saving S added at the end of each year, it's the smallest whole number of years t where
P(1 + r)ᵗ + S((1 + r)ᵗ − 1) ÷ r ≥ F ÷ (1 + r)years to retirement − t
Barista FIRE assumes you keep some part-time income after you leave full-time work. Your savings only need to cover the rest: F = (spending − part-time income) ÷ withdrawal rate.
Worked example
You're 30 and want $40,000 a year from 65. At 4% the FIRE number is $1,000,000. At a 5% real return over 35 years, 1.05³⁵ = 5.516, so the Coast number is 1,000,000 ÷ 5.516 = $181,290. With $100,000 invested and $10,000 a year added, you reach it after the deposit at the end of year 11, at age 41. With $20,000 of part-time income in retirement, the target halves to $500,000 and the Coast number to $90,645, which $100,000 already beats.
Limitations
- A steady real return is an assumption. A bad decade early on can leave you short, so many people keep a margin above their Coast number.
- Coasting means your job still pays all your bills until retirement, and nothing is saved for big one-off costs.
- Barista FIRE assumes the part-time income lasts as long as you need it.
A planning estimate, not financial, tax or investment advice. Every assumption is listed under the result.
Sources
How we checked this
Before every update, this calculator is run in a real browser with these known answers, and it must match all of them:
- Age 30, retire at 65, $1,000,000 target at 5% real: Coast number $181,290 ✓
- From $100,000 saving $10,000 at the end of each year, Coast age 41 (after 11 deposits) ✓
- Age 60, $900,000 + $100,000 deposit at the end of the year: Coast age 61 ✓
- 0% return, $30,000 a year from $100,000 to $1,000,000: 30 years, age 60 ✓
- Barista FIRE with $20,000 part-time income: $90,645, already hit ✓
- Age 45 with $800,000: coasts to $1,250,000 by about 54.1 ✓
- Part-time income covering all spending is caught ✓
Last checked October 26, 2026. Spotted something wrong? The math is done in your browser with the formula shown on this page, so you can check any result by hand.
Questions people ask
What is Coast FIRE?
Having enough invested that, with no more contributions, it grows to your full retirement number by your target age. You still work to cover today's spending, but you no longer need to save for retirement.
How do I calculate my Coast FIRE number?
Divide your FIRE number by (1 + real return) raised to the years until retirement. $1,000,000 needed in 35 years at 5% real: 1,000,000 ÷ 1.05³⁵ ≈ $181,290.
What is Barista FIRE?
Leaving full-time work while keeping a part-time job that covers part of your spending, often for health insurance. Your savings only need to cover the rest, so the target is smaller.
What's the difference between Coast FIRE and FIRE?
With FIRE your investments already cover your spending, so you can stop working. With Coast FIRE they'll cover it later, at your target age, as long as you don't touch them before then.