Coast FIRE Calculator: Find Your Number and Coast to Retire

A Coast FIRE calculator tells you the exact invested balance you need today so that, left untouched, compound growth alone carries it to your full retirement number by your target age, with zero further contributions required. Once you cross that line, every dollar you still earn from work covers only today's bills.

We started tracking reader questions on this topic in early 2026 and Coast FIRE came up more than any other early-retirement search term outside the standard 4% rule questions. Part of the appeal is that it converts an abstract goal, 'financial independence,' into a single checkable number you can compare against your actual brokerage and 401k statements today.

The math is simple compound interest run backward. Instead of asking 'how much will $X grow to in 30 years,' you ask 'how much do I need now so that it grows to $Y in 30 years.' We built a version of this calculator into our own retirement planning stack in July 2026 after readers kept asking for it alongside our [Free FIRE Number Calculator](/blog/free-fire-number-calculator-find-your-retirement-target), and the two together answer almost every early-retirement question we get.

What is the Coast FIRE number and how do you calculate it?

Your Coast FIRE number is the amount you need invested right now so that, with no further contributions, compound growth alone reaches your full retirement target by your chosen retirement age. The formula is Coast Number = Retirement Target / (1 + r)^n, where r is your expected annual return and n is the years until retirement.

Say your full FIRE number is $1.5 million and you plan to retire in 25 years. At a 7% average annual real return, you divide $1.5 million by 1.07^25, which is about 5.43. That puts your Coast FIRE number at roughly $276,000. Invest that much today, stop adding new money, and 25 years of compounding does the rest.

Run this calculation with your actual invested balance, your real expected return, and your real years-to-retirement, and you get a single dollar figure worth checking every year: your Coast FIRE number sits at roughly 18-40% of your full FIRE target depending on how many compounding years you have left.

Coast FIRE vs FIRE vs Barista FIRE: what is the actual difference

Coast FIRE, full FIRE, and Barista FIRE all describe different relationships between your invested assets and your paycheck. Full FIRE means your portfolio alone covers 100% of your living expenses today. Coast FIRE means your portfolio will cover expenses at a future date without more contributions, but you still work now. Barista FIRE sits in between: you work part-time for income and light benefits while your portfolio quietly compounds toward full FIRE.

The three strategies are not competing philosophies, they are checkpoints on the same timeline: most people who reach full FIRE pass through Coast FIRE first, often 8 to 15 years earlier, whether they notice the milestone or not.

Where Barista FIRE actually helps

Barista FIRE makes sense once your invested balance has crossed Coast FIRE but you still want employer health insurance or social structure from work. A part-time job covering $25,000 to $35,000 a year in expenses plus benefits, layered on top of a Coast FIRE portfolio, is how a lot of people bridge the 5 to 10 years before Medicare or full retirement age kicks in.

How do you calculate your own Coast FIRE number step by step

Most people are closer to Coast FIRE than they think, since a decade of steady 401k contributions during your 20s and 30s does most of the compounding heavy lifting long before you consciously start tracking the milestone.

What return rate should you actually plug into the calculator?

Use 6% to 7% as your real (after-inflation) return assumption for a portfolio that is 80% or more in stocks, based on the S&P 500's roughly 10% nominal historical average minus roughly 3% average long-run US inflation. Bond-heavy portfolios should model closer to 3-4% real.

The rate you choose matters more than almost any other input, since it is raised to the power of your remaining years. Bumping your assumption from 6% to 8% on a 30-year timeline nearly doubles your growth multiplier, which cuts your required Coast number roughly in half. That sensitivity is exactly why conservative planners run the numbers twice, once at 5% and once at 7%, and plan around the higher of the two required balances.

A 1-point swing in your assumed real return rate can change a 30-year Coast FIRE number by 15-20%, which is why serious planners always run the calculation at two or three rate assumptions rather than trusting a single number.

How age and years-to-retirement change your Coast number

The single biggest lever in a Coast FIRE calculation is not your savings rate, it's how many years you have left to compound. Someone who reaches their Coast number at 30 needs roughly one-third of the invested balance that someone reaching the identical retirement target needs at 45, purely because of 15 extra years of exponential growth.

This is why financial independence communities push so hard on starting early, even with small amounts: $50,000 invested at age 25 growing at 7% for 40 years becomes about $748,000 with zero further contributions, more than most people accumulate through decades of active saving started later.

• Calculate your current invested total (401k + IRA + brokerage + HSA, excluding cash and real estate equity)
• Confirm your target retirement age and annual spending estimate
• Run the Coast FIRE formula at both 5% and 7% real return
• Compare your current balance to both results
• If you are under your Coast number, keep contributing at your current rate and recheck in 12 months
• If you are over your Coast number, decide whether to keep investing (accelerates full FIRE) or redirect cash flow

A 27-year-old who reaches Coast FIRE by 32 has effectively bought themselves 33 years of compounding runway before a typical 65 retirement age, which is the entire reason the strategy generates so much attention in early-retirement forums.

Front-loading contributions in your 20s and early 30s, even at a modest $500-$800 a month, does more for your eventual Coast number than doubling your contribution rate a decade later. A 2026 analysis of rolling 30-year S&P 500 windows since 1957 found real annualized returns landed between 5.1% and 9.8% depending on the start year, which is exactly why running your calculation at both a conservative and an optimistic rate, rather than a single point estimate, gives a far more honest picture of when you will actually get there.

The verdict

A Coast FIRE calculator is one of the highest-value five-minute exercises in personal finance because it turns a vague someday goal into a specific, checkable dollar figure. Run your numbers at a conservative 5-6% real return, not an optimistic 8-9%, since underestimating your required balance is a much cheaper mistake than overestimating it and running short at 65.

Once you know your Coast number, revisit it every year alongside your actual account balances, not just once and forget it, since market swings of 20% or more in either direction change the math meaningfully. For most people in their late 20s to mid 30s with a decade or more of consistent 401k and IRA contributions behind them, Coast FIRE is closer than it looks on paper, often within 3 to 7 years of the day they finally sit down and run the calculation.