Imagine this: you wake up one day and your retirement is already funded. Not because you have enough to retire now — but because the money you've already invested will grow, on its own, into exactly what you'll need at 65. You could stop contributing entirely and still land on time.

That's Coast FI. And for tech employees who front-loaded their savings in their twenties and thirties, it can arrive a lot earlier than they'd guess. It's one of the most freeing numbers in personal finance, and almost nobody calculates it.

What Coast FI actually means

Most FIRE math is about reaching the full finish line — the portfolio big enough to live off forever. Coast FI is a different, earlier milestone. It's the point where your existing investments, left completely alone, will compound into your full retirement number by your target date — without another dollar of contributions.

You're not retired. You still have to cover your living expenses. But you no longer have to save for retirement. The heavy lifting is done; from here, your portfolio coasts.

That changes everything about your options. Coast FI is what makes it safe to take the lower-paying job you'd actually enjoy, go part-time, take the startup swing, or take a real sabbatical — because your future self is already taken care of. This is the "professional permission to make your move" I talk about, expressed as a single number.

How to calculate your Coast FI number

Two steps.

Step one: find your full FI number. Estimate your annual spending in retirement and multiply by 25 (the rough inverse of a 4% withdrawal rate). If you expect to spend $100,000 a year, your full number is about $2.5 million.

Step two: discount it back to today. Coast FI asks how much you'd need invested right now so that it grows into that $2.5M by retirement, with no further contributions. You divide your full number by growth over the years you have left.

A worked example. You're 35, you want to retire at 65 — that's 30 years of growth. Assume a 7% real return (a common planning assumption, not a promise). Over 30 years, money roughly grows 7- to 8-fold in real terms. So your Coast FI number is about $2.5M ÷ 7.6 ≈ $330,000.

Read that again. If a 35-year-old has roughly $330K invested, they could never save another cent for retirement and still plausibly hit $2.5M by 65. For a lot of tech professionals who loaded up their 401(k) and brokerage early, that number is already in the rearview mirror — they're Coast FI and don't know it.

These are planning assumptions, not guarantees — returns vary, inflation bites, and your spending estimate is the biggest swing factor. But the framework is sound, and the realization is often life-changing.

Why "before 40" matters

The earlier you hit Coast FI, the more of your high-earning years become optional rather than required. That's the whole point. Hitting it at 38 instead of 52 doesn't mean you stop working — it means you get to choose work on your terms for a decade-plus, while compounding quietly finishes the job in the background.

It also reframes risk. Once you're Coast FI, a pay cut to do something you love isn't a threat to your retirement — it's a lifestyle choice your plan can absorb. The anxiety that keeps so many high earners chained to a job they've outgrown starts to dissolve.

The traps to watch

Coast FI is powerful, but two things break the math. First, lifestyle inflation: if your retirement spending estimate keeps climbing, your full FI number climbs with it, and your Coast FI number you "already passed" suddenly isn't enough. Second, touching the money: Coast FI only works if you actually leave the invested balance alone to compound. Raid it for a house down payment and you reset the clock.

And a reminder specific to tech: if a big slice of your "invested" number is concentrated company stock, your Coast FI number is riding on one company's fortunes. Coast FI on a diversified portfolio is a plan. Coast FI on a single stock is a bet.

Key takeaways

• Coast FI = the point where your current investments will grow into your full retirement number with zero future contributions.
• Calculate it in two steps: full FI number (spending × 25), then discount it back to today using your years-to-retirement and an assumed return.
• Many tech pros who saved early are already Coast FI and don't realize it — it's the math behind taking the lower-stress job or the sabbatical.
• It breaks if you let spending balloon or spend the balance — and it's only as safe as how diversified that balance is.

The move: Curious whether you're already Coast FI — and what that would let you do next? Book a Clarity Call and we'll run your number.

Educational only — not personalized financial advice. Return and inflation assumptions are illustrative; your results will differ.