Coast FIRE is the moment your portfolio is large enough that, without any new contributions, it can grow into a comfortable retirement on its own. Retirement Lab simulates that growth across 10,000 market paths and applies tax modeling to the eventual withdrawal phase.
Project my coast numberTraditional FIRE asks the bigger question: how much do I need invested before I can stop working entirely and live off the portfolio? Coast FIRE asks a narrower question: how much do I need invested today so I can stop saving for retirement and let compounding finish the job, while my paycheck covers current spending? The two numbers are usually different — your coast number is smaller, because you still have years ahead during which the portfolio grows untouched.
If your intent is actually full financial independence — covering all spending from the portfolio at the moment you stop working — the FIRE calculator is the better fit. Coast FIRE is the right framing when you plan to keep earning enough to cover today, but want to know when you can stop adding to the retirement account.
If you want a target portfolio of target_at_retirement and you have years_to_retirement years for it to grow at an expected real return r, the Coast FIRE number is:
coast_fire_number = target_at_retirement / (1 + r)^years_to_retirement
For example, with a $1,000,000 inflation-adjusted target, 30 years to grow, and a 5% real return assumption, the Coast FIRE number is about $1,000,000 / (1.05)^30 ≈ $231,000.
Real markets do not return a flat 5% every year — sequence and shape matter. Retirement Lab replaces the single-rate estimate with 10,000 Monte Carlo paths drawn from a distribution calibrated to long-run global equity returns, including fat-tail risk. The output is a probability distribution of where your coast portfolio actually lands, not a single line.
Coasting only works if the after-tax draw covers your future spending. Retirement Lab models residency-country income tax, capital gains, and (where applicable) wealth taxes on the withdrawal phase, so the projection reflects the bracket you would actually retire into. See how the compound-growth and tax assumptions work for the full walkthrough.
Coast FIRE is the milestone where your invested portfolio is large enough that it can grow on its own into a comfortable retirement number — without any further contributions — given enough years and a reasonable expected return. Once you hit your coast number, future earnings can go toward current lifestyle instead of retirement savings, although nothing forces you to stop contributing.
The textbook formula is target_at_retirement / (1 + r)^years_to_retirement, where r is your assumed real (inflation-adjusted) return and years_to_retirement is how many years you have until you need the money. With a $1M target, 30 years, and 5% real returns, the coast number is about $231,000. Retirement Lab refines that single-rate estimate by simulating 10,000 market sequences for your inputs and modeling local taxes on the withdrawal phase, so the result is a probability distribution rather than one number.
Yes. The simulation applies bracket-based income tax, capital gains, and (where applicable) wealth tax for the residency country you choose, on the eventual withdrawal phase. That matters because a portfolio sized for a pre-tax target can fall short once you account for the bracket you actually retire into.
Monte Carlo simulation is built to answer this. Instead of one optimistic line, the simulation shows the full range — including the unlucky paths where returns disappoint. If too many paths fall short for your comfort, the model lets you tighten the inputs (more years, a higher coast balance, lower target spending) and re-run to see how the distribution shifts.