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Coast FIRE Calculator: Could You Stop Adding and Still Retire on Time?

Have you saved enough that you could stop adding and still retire on time? That point has a name, Coast FIRE, and it has a number. Type your age, what you have invested today, and what you plan to spend in retirement, and this page reads you your coast number: the amount that, left to grow with no new money added, reaches your full retirement number by your retirement age. The math runs in your browser; the numbers you type are never sent to us.

Your numbers

You and your retirement

Your current age

Age you plan to retire

Your current age has to be younger than your retirement age: the years between them are the years the pot gets to grow.

Your money

Invested today ($)

Everything you have invested for retirement, added together. Zero is an honest answer if you are starting now.

Yearly spending in retirement ($)

What a year of your retired life costs, in today's dollars. A rough figure is fine; you can test a leaner and a fuller one.

Your assumptions

Yearly return (%)

Your assumption, not a forecast and not a promise. Past returns do not guarantee future ones, so test a careful figure too.

Withdrawal rate (%)

The standard is 4 percent, a rule of thumb, not a promise. You can set it from 2 to 6 percent and watch the answer move.

Your coast number Your number is waiting

Type your numbers above to see your coast number.

Your retirement number $0 Yearly spending divided by your withdrawal rate.

Invested today $0 The pot this calculation grows, with nothing added.

Still to go $0 The distance between your pot and your coast number.

Crossing age 0 The age today's pot reaches your full retirement number, left alone.

Years to grow 0 years From your current age to your retirement age.

Coast number = retirement number divided by (1 + return) ^ years left.

The formula in plain words: your retirement number is what you need saved in total on the day you retire. Your coast number is the smaller amount you need today, because each year of growth does part of the work. Divide the big number by the growth over the years left, and the result is the amount that coasts the rest of the way on its own.

What this free calculator did not calculate. No 40-year year-by-year projection: this page gives you the headline numbers, not a year-by-year path. No withdrawal plan for the years after you retire. No taxes or investment fees. No inflation split: spending and returns are both in today's dollars, the simple standard way. The paid Coast FIRE spreadsheet runs the full 40-year projection behind the same verdict, year by year.

Take your coast number with you

Your coast number is above, and it is yours to keep. Join KOLLAZ Modern Money for one plain-number email a week, and get the free Know Your Date sheet as a welcome gift.

How the Coast FIRE calculator works

Updated November 2026

What Coast FIRE is

Coast FIRE is the moment your savings start carrying you. You have invested enough that, if you never added another dollar, the pot would still grow into your full retirement number by your retirement age. You are not retired at that point, and you still need income to live on. What changes is the job your income has to do: it only has to cover your bills, not fund your retirement too.

The formula, in plain words and symbols

Three steps, and the calculator above runs exactly these:

Step 1: your retirement number. retirement number = yearly spending in retirement / (withdrawal rate / 100). At the standard 4 percent rule of thumb, that is your yearly spending divided by 0.04, which is 25 times your yearly spending. The 4 percent figure is a rule of thumb, stated openly, not a promise.

Step 2: your growth factor. growth factor = (1 + return / 100) ^ years left, where years left is your retirement age minus your current age. At a 7 percent return over 30 years, the factor is about 7.61: a dollar invested today becomes about $7.61, if that return actually happens every year, which real markets never do so smoothly.

Step 3: your coast number. coast number = retirement number / growth factor. Because growth does most of the work over a long run, the coast number is far smaller than the retirement number, and it gets smaller the younger you are when you reach it.

The crossing age answers the same question from the other side: the age where the pot you already have, growing at your return with no new money added, reaches the full retirement number. If that age lands before your retirement age, you are past your coast number. If it lands after, the gap tells you how much more would put you on the line.

A worked example

Take the numbers this calculator opens with. Age 35, with $100,000 invested, planning to retire at 65 and spend $30,000 a year, at a 7 percent return and the standard 4 percent withdrawal rate.

Step 1: $30,000 / 0.04 gives a retirement number of $750,000.00. Step 2: (1 + 0.07) ^ 30 years gives a growth factor of about 7.61. Step 3: $750,000.00 / 7.61 gives a coast number of $98,525.34. The $100,000 already invested is past that line by $1,474.66. Left alone, that pot reaches the full $750,000.00 at age 64.8, just before the planned retirement age of 65. Change any one input and every one of those numbers moves; that is what the fields above are for.

How to read your result

Your coast number is the headline: the amount that needs to be invested today, on your assumptions. The gap is how far your current pot sits from it, or how far past it you already are. The crossing age is the same story told as an age: when today's pot, left alone, reaches the full retirement number. Test a lower return before you trust a cheerful answer; a coast number that only works at a high return is not a safe place to coast from.

What the math takes as given, and what it leaves out

The math holds your return steady every year, which real markets never do, and it works in today's dollars, with no split for inflation. It leaves out taxes, investment fees, pensions and government benefits, and any money you add from here on. It is a headline check, priced honestly: it tells you whether you are on the line, not what every year between here and retirement will look like.

The claiming side of the same retirement

Coast FIRE answers the saving side: have you saved enough. The claiming side, when to start Social Security so the later, bigger checks pull ahead, is a different formula with its own break-even age. The free Social Security break-even calculator answers that side of the same retirement, from your own benefit figure.

Sources

The method is the standard Coast FIRE definition: the retirement number from the withdrawal rate, discounted back over the years left at the assumed return. It is the same method the paid workbook states on its own cover: Coast FIRE Calculator Spreadsheet (Kollaz, KM-028), "the standard 4 percent rule of thumb, stated openly".
The 4 percent figure is a rule of thumb for sizing a retirement pot, labelled as one everywhere on this page. It is not a guarantee, and this calculator lets you replace it with any rate from 2 to 6 percent.

Educational information only, not financial advice. Consider a qualified professional for decisions about your specific situation.

Frequently asked questions

What is Coast FIRE?

Coast FIRE is the point where the money you have already invested is enough, on its own, to grow into your full retirement number by your retirement age. Past that point you could stop adding new money and still arrive on time, as long as the return you assumed actually happens. You still need to cover your bills until then, which is why many people pair it with work they mind less.

What is a coast number?

Your coast number is the amount you need invested today to be at that point. This page works it out in two steps: your retirement number (your yearly spending in retirement divided by your withdrawal rate) divided by your growth factor, (1 + return) ^ years left until retirement. The further away retirement is, the smaller the coast number, because the pot has more years to grow.

What return should I assume?

That is your call, and this page treats it as your assumption, never as a forecast. The return field is editable so you can test a careful figure and a hopeful one and watch the coast number move. Past returns are not a promise of future returns, and a plan that only works at a high return is a plan that needs more saving, not more hope.

What does the 4 percent rule mean?

It is a rule of thumb that says a retirement pot can pay out about 4 percent of its value per year. Turned around, it sizes the pot: yearly spending divided by 4 percent gives a retirement number 25 times your yearly spending. It is a rough guide, not a promise and not a guarantee. This calculator lets you set the rate from 2 to 6 percent so you can see how much the answer moves.

Where does my information go when I use this calculator?

The calculation runs entirely in your browser on your own device, and the numbers you type are never sent to us or stored. Like every Kollaz page, this one counts visits with cookies only if you accept them; the consent banner explains that choice, and it is yours to decline. The signup form on this page sends only the email address you type into it, and your first name if you add it, when you press its button. Signing up takes one more step: we email you a link, and clicking it is what subscribes you.

Is this financial advice?

No. It is arithmetic on the numbers you type, using the standard Coast FIRE formula. It does not know your debts, your health, your pension, or your life. For decisions about your specific situation, talk to a qualified professional.