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How OrbitFire works

Every step and assumption behind your answer, the questions people ask most, what the types of FIRE mean, and a patch to share your progress without sharing your numbers.

How we calculate

Three numbers, no black box. Here is every step and every assumption, with sources.

  1. Your FIRE number

    Yearly spending divided by a withdrawal rate. The classic 4% rule (25 times spending) was built for 30-year retirements, so the rate slides down to 3.25% for a 60-year one, rounded down to the nearest 0.05%. Retiring at 45 uses 3.5%.

  2. Your Coast FIRE number

    What you'd need invested today so that, with no more saving, growth reaches your FIRE number by your retirement age. It's your FIRE number discounted by the expected return over the years left.

  3. Your stop-saving age

    We grow your investments year by year at your saving rate and find the first year they reach the coast line. We repeat it at returns 2 points lower and higher to show the range.

What we assume

  • Everything is in today's dollars. Returns are after inflation (5% in the middle case, adjustable).
  • What you invest stays the same each year in today's dollars, added at the end of each year. No raises.
  • Plans are sized to last to age 95.
  • Returns are steady in the Coast calculator. Life phases tests 1,000 bumpy markets instead.
  • Life phases can also run your plan through past US markets, once for every start year since 1928. Each year of the plan gets what stocks (the S&P 500 with dividends) and bonds (10-year Treasuries) returned that year, from Aswath Damodaran's "Historical Returns on Stocks, Bonds and Bills" (NYU Stern), less that year's inflation from the Bureau of Labor Statistics' consumer price index and your yearly fee. Only start years with enough record to reach 95 are counted. The past is one history, not a forecast.
  • One plan feeds every page. Income you add (stock vests, military pay, rent, a pension, Social Security) lowers what your investments have to cover, so Mission Control and every system show the same Coast and FIRE ages.
  • Taxes in retirement count only when you pick a rate under Fine-tune; "Not counted" is the default. Social Security counts only once you add it, so leaving it out is a safety margin.
  • Fine-tune can estimate that tax rate from your plan. It takes one year of retirement, draws from pre-tax, Roth and taxable accounts in proportion to what you hold, and counts pre-tax withdrawals and pensions as ordinary income, half of each brokerage withdrawal as long-term gain, and Social Security under the IRS combined income rule. Then it applies the 2026 federal standard deduction, brackets and capital gains thresholds, and repeats the sum because the tax has to be withdrawn too. It's an estimate for planning, not tax advice: it leaves out state rules beyond one flat rate, penalties before 59½, required distributions and future law changes.
  • Health insurance before 65 counts if it's in your spending. Healthcare + bridge prices it and checks you can reach enough money before 59½.

Sources

OrbitFire is independent. Nobody pays to change a result, your numbers are never tracked or readable by us, and we don't sell data. Rule figures are for 2026, last checked November 2026.

Questions people ask

What does FIRE stand for?

Financial Independence, Retire Early. The idea is to invest enough that your portfolio can pay for your life, so working becomes optional. Many people in the FIRE community keep working after they get there, just on their own terms.

What is Coast FIRE?

The point where you have enough invested that, if you never added another dollar, normal market growth would still get you to your FIRE number by your target retirement age. From there you only need to earn enough to cover current expenses, which is why it's popular with people who want to take a lower-stress job or work part time.

What is Mission Control?

Your plan's home screen once you've entered your numbers. Each part of your plan (savings, stock pay, military pay, Social Security, healthcare and the bridge to 59½, life phases, property) reports to it as GO, HOLD or OFF with one line on why, and it lists the one to three things that would change your answer most. Every page shows the same stage, Coast age and FIRE age, because they all read the same plan.

What's the demo mission?

An example plan for a 33-year-old tech worker with stock pay, a rental and a part-time stretch before retiring at 52. Open it from the homepage to look around Mission Control and every system before typing a number. Nothing in the demo is saved, and your own plan isn't touched while you explore.

Why is my FIRE number more than 25 times my spending?

25 times spending comes from the 4% rule, which studies of historical US returns (the best known is the 1998 Trinity study) built for 30-year retirements. Early retirees need their money to last 40 to 60 years, and research on those horizons found 4% held up only about two thirds of the time over 60 years. So OrbitFire matches the withdrawal rate to how long your retirement lasts: 4% for 30 years or less, then 3.75%, 3.5% and 3.25% for longer ones. You can switch it off under Fine-tune and set your own.

Why assume a 5% return, and why show a range?

It's an after-inflation figure, so it already accounts for prices rising. US stocks returned about 6 to 7% a year after inflation over the last century, but the big firms' 2026 forecasts for the next decade work out lower, roughly 2 to 4%. 5% sits between them. Because one rate compounded over decades can move your Coast FIRE number by 3 times or more, every result also shows a window at 2 points lower and higher.

Are amounts in today’s dollars or future dollars?

Today's dollars, everywhere. Returns are after inflation, so a $2M FIRE number means $2M of today's buying power. Where it helps, OrbitFire also shows the future-dollar equivalent at 2.5% inflation. Mixing the two is the most common reason Coast FIRE calculators disagree with each other.

Does it include taxes, health insurance and Social Security?

Yes, once they're in your plan. Pick a retirement tax rate under Fine-tune and every answer covers spending plus that tax; it's off by default because the right rate depends on which accounts your money is in. Social Security counts once you add it from the Social Security system, and it's left out until then as a safety margin. Healthcare + bridge prices health insurance before 65 and checks the years before 59½, and Stock pay works out the tax on each vest before adding it.

Is my information stored anywhere?

Your exact numbers stay on your device (or, with sync on, are encrypted first so only you can read them), and we don't sell data. Every calculation runs in your browser. To learn how people use OrbitFire, we keep rough ranges of what's entered (like age 30 to 34, or $100k to $250k invested), never the exact figures and never tied to you or an account. If you leave "Remember my numbers on this device" on, they're kept in this browser's own storage so a reload doesn't lose them; "Forget them now" erases them. "Copy link to my plan" puts your numbers in the part of the link after the #, which browsers never send to websites, so anyone you give that link to can see them. To show progress without numbers, share your mission patch. If you have an account and turn on sync, your plans are encrypted on your device with a passphrase only you know before they're stored, so they follow you to your other devices but OrbitFire can't read them.

What does OrbitFire keep about me?

Without an account, nothing that points to you. We keep counts per day on our own server: which page, which site linked here, phone or computer, state or country, which steps people take, rough ranges of what's entered (like age 30 to 34), and answers to the one optional question we ask ("What are you planning for?"). There are no cookies or IDs, so nothing is tied to a person, and exact numbers are never sent. Browsers that send Global Privacy Control or Do Not Track aren't counted at all. If someone invites you and you make an account, it holds your email address, and you choose whether to get occasional updates (off unless you tick the box).

Five flavors of FIRE

The FIRE community has split the goal into versions that mostly differ by how much you plan to spend. We stack them like altitudes, from Lean at the bottom to Fat at the top, so a result always tells you where you are.

  1. MARSFat FIRE$100k or more a year in retirement, which means a portfolio of roughly $2.5M to $3M. Comet gets a tiny rover.
  2. THE MOONFIRE25 to 31 times your yearly spending, invested, depending on how long retirement lasts. At that size the portfolio pays for life and work becomes optional.
  3. SPACE STATIONBarista FIREInvestments cover most of your spending; a part-time job covers the rest, often chosen for the health insurance. You docked, you didn't land.
  4. ORBITCoast FIREYou have enough invested that, with zero new contributions, growth alone reaches your FIRE number by your retirement age. From here you only need to cover today's bills. This is the one the Coast calculator measures.Run it
  5. LOW ORBITLean FIRERetire early on about $40k a year or less, so roughly $1M to $1.2M invested. Possible, but the budget stays tight for good.

Your mission patch

It shows your stage, how far you are toward Coast FIRE and the year. It never shows a dollar amount, so you can post it without telling the internet what you make.

The patch follows your plan as it changes. Save it as a picture, or share it straight to another app where your browser offers that. The share text links to a blank calculator, not to your numbers. Make a new one each year to track the climb.