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Coast FIRE Calculator

Most FIRE calculators tell you when you're done. This one finds the age you can stop contributing and let compound growth do the rest. Enter your target retirement age and see exactly when you can coast.

Your age right now. This is your starting line.

Everything you've already invested toward retirement.

What you invest each month. Annual contribution is this × 12.

The age you want to be fully financially independent.

Safe withdrawal rate (SWR) is the share of your portfolio you draw down each year. 4% is the classic Trinity-study guideline; go lower for more cushion.

Long-run stock returns run about 7–10%. Enter a nominal rate; inflation is handled separately below.

How fast prices climb. The US long-run average is about 2.5–3%.

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How We Calculate This

Coast Number (today's dollars)

Your Coast Number is the portfolio balance you need today so that, without adding another dollar, compound growth alone carries it to your FI Number by your target retirement age:

Coast Number = FI Number ÷ (1 + r)n

where r is your expected annual return and n is the number of years between today and your target retirement age. The FI Number itself is monthly spending × 12 ÷ safe withdrawal rate (the classic 25× rule at a 4% SWR).

FI Number and the inflation-adjusted target

The FI Number (monthly spending × 12 ÷ SWR) is stated in today's dollars. Because the projection is in nominal dollars, the calculator inflates that target forward year by year:

FI Targetn = FI Number × (1 + inflation)n

Your Coast Age is the first year your portfolio, growing at the expected return, would reach that moving nominal target by your target retirement age if you stopped contributing right now. The year-by-year table shows the annual snapshots of this model.

How the coast age is found

The calculator runs a year-by-year simulation. Each year it asks: if I stopped contributing right now, would my current portfolio compound to the FI Target by the target retirement age? The first year the answer is yes is your Coast Age. Unlike calculators that require you to guess a coast date, this one finds it for you.

After coasting: nominal growth to retirement

Once you hit your Coast Number and stop contributing, the projection shows your portfolio growing by the expected return alone. At your target retirement age the balance should equal your nominal FI Target: the amount that, drawn down at your SWR, covers your monthly spending in tomorrow's dollars.

Current progress

Current progress is your current savings divided by your Coast Number. Reaching 100% means you are already coasting, with no more contributions needed. Below 100% the projection shows how long it takes your savings-plus-returns to close the gap.

Coast FIRE Calculator Formula

Your Coast Number is the lump sum you need today so that compound growth carries it to your FI Number by your target retirement age, with no further contributions required:

Coast Number = FI Number ÷ (1 + r)^n

where r is the expected annual return (decimal), n is the years between today and your target retirement age, and FI Number = Monthly Spending × 12 ÷ Safe Withdrawal Rate.

How to Use This Calculator

  1. Enter your Current Age and Current Savings / Investments.
  2. Enter your Monthly Savings / Investment, the amount you currently invest each month.
  3. Enter your Monthly Spending in Retirement, your expected monthly expenses once fully financially independent.
  4. Enter your Target Retirement Age, the age you want to be fully financially independent.
  5. Enter your Safe Withdrawal Rate (4% is the classic Trinity Study guideline), Expected Annual Return, and Inflation Rate.
  6. Click Calculate to see your Coast Number, your Coast Age, a timeline chart, and a year-by-year projection.

Frequently Asked Questions

What is Coast FIRE?

Coast FIRE is a milestone on the path to financial independence: you have saved and invested enough that, even if you never add another dollar, compound growth alone will carry your portfolio to your full FI Number by your target retirement age. After reaching your Coast Number you can stop contributing and let the math work, while still earning enough to cover current expenses.

What is a coast number?

Your coast number is the portfolio balance you need today so that it grows, without any further contributions, to your full FI Number by the time you plan to retire. It is the present value of your FI Number, discounted by your expected return over the years between now and retirement. A higher expected return or a longer runway to retirement means a lower coast number.

How is the coast age found?

This calculator simulates your portfolio year by year, adding your annual savings (your monthly savings × 12) and applying your expected return. Each year it checks: if you stopped contributing right now, would your current balance grow to your FI Number by your target retirement age? The first year the answer is yes is your Coast Age. You give it a target retirement age; it finds the contributing-stop date for you.

FIRE vs Barista FIRE vs Coast FIRE: when should I use each?

All three strategies share the same end goal of financial independence, but differ in what they optimize for:
  • FIRE Calculator: finds the age your full portfolio covers 100% of spending with no earned income. Use it if you want to retire fully as soon as possible.
  • Barista FIRE Calculator: finds the age a reduced portfolio (funded by part-time income covering the gap) lets you leave full-time work. Use it if you plan to keep some part-time income in semi-retirement.
  • Coast FIRE Calculator (this page): finds the age you can stop investing and let growth do the rest, while you still work (or not) to cover current expenses. Use it if your goal is to reach a point where you owe nothing more to your future self.

Why does the coast number grow as I get older?

Your coast number is the present value of your FI Number, discounted back from your target retirement date. The closer you are to retirement, the less time compound growth has to work, so you need a larger lump sum today to reach the same future target. Put differently: every year you wait, the coast number you must hit rises. That is why starting early shrinks the mountain you need to climb.

Do I really stop investing after I hit my coast number?

You can, but you do not have to. Coast FIRE simply means you no longer need to invest more for retirement. Your existing balance is mathematically sufficient. Many people keep investing because they earn more than they spend, want to retire earlier than planned, or simply prefer the safety margin. Coast FIRE is a freedom milestone, and stopping is your choice.

Why are the numbers shown in nominal (not inflation-adjusted) dollars?

The projection uses nominal dollars and compounding, which matches how real brokerage balances look. Inflation enters the model by growing the FI Target forward each year, so when your portfolio catches up to that target, both numbers are expressed in the same nominal terms. Showing real (inflation-adjusted) dollars can look misleading because your balance appears to shrink even when it grows.

What if I can't coast to FI by my target retirement age?

If your savings and monthly contributions are not on track to reach the coast number before your target retirement age, the calculator shows your projected growth anyway and tells you so clearly. Options to improve the result: increase monthly savings (closes the gap faster), reduce target monthly spending in retirement (lowers the FI Number and therefore the coast number), assume a higher expected return, or push back the target retirement age (more time for growth).

How does Coast FIRE relate to my savings rate?

Your savings rate (monthly savings divided by monthly savings plus monthly spending) is the biggest lever on how quickly you reach your coast number. A higher savings rate both accelerates portfolio growth and signals lower spending in retirement, which shrinks the FI Number and therefore the coast number you need to hit. See the FIRE Calculator for the relationship between savings rate and years to FI.

Glossary: key terms used on this page

  • Coast FIRE: The milestone at which your invested portfolio will grow, without further contributions, to your full FI Number by your target retirement age.
  • Coast Number: The lump sum you need invested today to coast: FI Number divided by (1 + r)^n, where r is expected return and n is years to retirement.
  • FI Number: The portfolio size at which a safe annual withdrawal covers your retirement spending. At a 4% SWR it equals your annual spending × 25.
  • SWR: Safe Withdrawal Rate. The percentage of your portfolio you withdraw each year. The 4% guideline comes from the Trinity Study.
  • Nominal dollars: Dollar values that have not been adjusted for inflation, matching what your account balance actually shows.

Further Reading

Related Calculators

Savings Goal Calculator

Calculate how much you need to save each month to reach your financial goal on time.

FIRE Calculator

Find your financial independence number, see how many years until you can retire early, and track your progress year by year.

Barista FIRE Calculator

Most Barista FIRE calculators make you guess a semi-retirement age. This one finds it for you. Enter your numbers and see exactly when part-time income plus your portfolio cover your spending.