Coast FIRE Calculator
Introduction to Coast FIRE
Coast FIRE is a milestone for people who want retirement flexibility before they want full retirement. The goal is to build a portfolio large enough that, with enough time left on the clock, it can grow into your eventual financial independence target even if you stop making new retirement contributions later.
This calculator estimates the Coast FIRE number by first projecting a full FI target from your retirement spending goal and then discounting that target back to today with your assumed annual return and years to retirement. Once you have the answer, you can compare it with your current investments and see whether compounding alone may do the rest.
That makes Coast FIRE useful for decisions that are really about optionality. People use it to judge whether they can lower retirement contributions, move money toward a house or family expenses, shift into part-time work, or take a lower-stress job without losing sight of the long-term retirement plan.
How to Use the Coast FIRE Calculator
Start with the two ages that define your runway: your current age and your target retirement age. The longer the gap, the more time your Coast FIRE portfolio has to compound, which usually reduces the amount needed today. A shorter runway does the opposite and pushes the Coast number higher.
Enter the retirement spending you want your portfolio to support in today's dollars, then add the amount you already have invested for retirement. Finish with an expected annual return. If you are unsure about the return, it is often smarter to test several assumptions than to trust one optimistic estimate, because Coast FIRE is very sensitive to compounding.
When you calculate, the result panel shows your FI target, your Coast FIRE number, whether your current balance is above or below that threshold, and the projected future value of your existing savings. If the result feels close, rerun it with a lower return, higher retirement spending, or an earlier retirement age to see how fragile the plan really is.
Formula for Coast FIRE
The Coast FIRE calculation uses a straightforward two-step model built around the 4% rule. First, it converts expected annual retirement spending into a rough financial independence target by multiplying that spending by 25. In other words, the future FI amount is the spending goal that your portfolio ultimately needs to reach.
After the FI target is estimated, the calculator works backward to find how much needs to be invested today so that balance can grow to the target by retirement without any further contributions. That is the Coast FIRE number, and it is found by discounting the future FI amount over your remaining years to retirement.
The same relationship in MathML form is:
In that expression, F is the FI target, C is the Coast FIRE number, r is your assumed annual return, and n is the number of years until retirement. Longer compounding periods reduce the required amount today; higher spending goals, lower returns, or a shorter runway increase it.
Coast FIRE Example
Imagine you are 35, plan to retire at 65, expect to spend $40,000 a year in retirement, and use a 7% average annual return. The calculator first turns that spending goal into a full FI target using the 4% rule, which gives a portfolio goal of about $1,000,000.
With 30 years of compounding ahead, that future million-dollar target discounts back to roughly $131,000 today. So if your current invested balance is around that level, and if your portfolio really does average 7% over the full period, your savings could grow into the FI target without any new retirement contributions. If your balance is lower, the gap is the Coast FIRE amount you still need to build.
How to Interpret Your Coast FIRE Results
Treat the result as a planning threshold, not a life sentence. If your savings are below the Coast FIRE number, your portfolio is not yet expected to reach your FI target on its own, so you probably still need contributions, more years of work, lower retirement spending, or some combination of those levers.
If you are close to the threshold, the calculation is especially sensitive. Small changes in returns, fees, taxes, inflation, or the lifestyle you want in retirement can move you above or below Coast FIRE, so being near the line is a cue to review assumptions rather than a reason to assume the answer is settled.
If your current balance is above the Coast FIRE number, then under the assumptions you entered, future retirement contributions may no longer be necessary. That still does not mean you can retire immediately; it means your current investments may be large enough that you can stop adding to them and let compound growth carry the account the rest of the way.
Limitations of the Coast FIRE Estimate
This calculator keeps the Coast FIRE math intentionally simple so it is quick to use, but real life is messier. It assumes a steady average return, even though market results arrive in uneven bursts, and it assumes that you neither add to nor withdraw from the portfolio after the point you decide to coast.
The calculator also uses the 4% rule as a planning shortcut rather than a promise. Some people prefer a lower withdrawal rate for a larger margin of safety, and that choice changes both the FI target and the Coast FIRE number. It also does not model taxes, account type differences, investment costs, pension income, Social Security, sequence-of-returns risk, or major changes in spending.
For that reason, the most useful way to use the calculator is to compare scenarios. Try a conservative return, your base case, and a more optimistic case. Then test earlier or later retirement ages and see which assumption moves the result the most. The biggest sensitivity usually tells you where your plan needs the most attention.
Example Coast FIRE Scenarios by Time Horizon
The table below shows how much of a Coast FIRE balance is needed today for several FI targets and retirement timeframes, assuming a 7% annual return. As the number of years to retirement increases, the required amount falls because compound growth has more time to do the heavy lifting.
| Years to retirement | FI goal: $750,000 | FI goal: $1,000,000 | FI goal: $1,500,000 |
|---|---|---|---|
| 20 years | $193,877 | $258,503 | $387,754 |
| 25 years | $138,017 | $184,023 | $276,035 |
| 30 years | $98,525 | $131,367 | $197,050 |
| 35 years | $70,268 | $93,691 | $140,536 |
These are reference points, not prescriptions. Change the return assumption or the withdrawal rule and every number shifts, but the table is still useful for seeing how quickly the Coast FIRE threshold moves when you shorten or lengthen the runway.
Coast FIRE vs. Traditional FIRE
Coast FIRE and traditional FIRE are both about financial independence, but they solve different planning problems. Traditional FIRE asks how quickly you can build the entire nest egg needed to stop working, while Coast FIRE asks how early you can reach a point where later contributions become optional.
In practice, Coast FIRE often means heavier saving early and more freedom later. Traditional FIRE usually means keeping the savings rate high until the full target is reached. The difference is less about whether retirement matters and more about whether flexibility arrives before or after work ends.
Neither path is better for everyone. Coast FIRE can fit people who want room to breathe while they are still working; traditional FIRE can fit people who want a cleaner, earlier exit from paid work.
Using This Coast FIRE Calculator in Planning
A good Coast FIRE plan compares several realistic futures instead of pretending there is only one correct answer. Try a base-case return, a conservative return, and a more optimistic one. Then see how much the Coast number changes if you retire earlier or expect higher retirement spending.
It also helps to revisit the calculation over time. As your portfolio grows, your career changes, and your retirement lifestyle becomes clearer, the Coast FIRE threshold will move with you. The point is not to memorize a single number; it is to understand how much flexibility your current savings are already buying.
Who Coast FIRE Works Best For
Coast FIRE often resonates with people who saved aggressively early, value future flexibility, and would rather buy options than chase immediate retirement. It can be especially appealing in your 20s or 30s if you have a stable income, can save a meaningful portion of it, and want the freedom to scale back work later instead of racing to quit altogether.
It may be less compelling if your income is highly uncertain, your spending needs are likely to change a lot, you expect to support others for many years, or you prefer a more conservative portfolio with lower long-run growth. In those cases the Coast number can still be useful, but the safe margin usually needs to be larger.
Important Coast FIRE Disclaimer
This Coast FIRE calculator is for educational illustration only and is not personalized investment, tax, legal, or financial advice. The result depends on the inputs you provide and on simplified assumptions about spending, returns, and retirement timing, so real-world outcomes can differ substantially.
Before making major decisions such as changing jobs, reducing savings, or retiring, consider speaking with a qualified financial professional who can review your complete situation and stress-test the assumptions behind your Coast FIRE plan.
Mini-Game: Coast the Portfolio
If you want to feel the Coast FIRE tradeoff instead of just reading the formula, this optional mini-game turns the idea into a fast visual challenge. Your portfolio line moves toward retirement while the glowing Coast line marks the balance needed to stop contributing and let compounding do the rest. Hold the screen, mouse, or spacebar to add savings. Release to coast. The best runs cross the line early and stay above it through market swings and expense shocks.
Controls: hold or tap anywhere on the game to contribute, then release to coast. Keyboard fallback: hold the spacebar to contribute. A run lasts about 75 seconds.