How much do you need saved to Coast FIRE?

02/02/2026·14 min read

Coast FIRE is a variant of the FIRE movement where you save aggressively early so that your investments can grow to cover retirement expenses later without any further contributions.

We won't dive into the full concept here, so if you're unfamiliar with Coast FIRE, check out our guide: What is Coast FIRE?

This article focuses on the math behind Coast FIRE and how to calculate your Coast FIRE number.

We will go over:

1. The formula
2. Real examples
3. Age-based scenarios
4. How to calculate your own number

If you want to skip the math and test with your own numbers right away, try our interactive tool.

The Coast FIRE Formula

Coast FIRE is calculated in two steps.

Step 1: Find your retirement number

Retirement number = annual retirement spending ÷ withdrawal rate

Example:

This is the same math used in Traditional FIRE.

Step 2: Discount back to today

You now calculate how much you need invested today so that compounding reaches that number by retirement age.

Coast FIRE number:

Retirement number ÷ (1 + growth rate)^years

Example:

• Retirement goal: $2,000,000
• Years until retirement: 30
• Expected growth: 7%

Growth factor ≈ 7.6

$2,000,000 ÷ 7.6 ≈ $263,000

That means, if you invest $263k and never contribute another dollar, it can grow to $2M by your retirement age.

That is your Coast FIRE number.

How Age Changes the Number

In investing and compound interest, time is absolutely everything.

The younger you reach Coast FIRE, the smaller the required portfolio.

Example: $2M retirement target at 7% return

As you can see, the amount needed to Coast FIRE grows exponentially as you age.

Compounding is incredibly powerful, but it needs time to fully work its magic. This concept applies to all investing, not just Coast FIRE.

What If Returns Are Lower?

Coast FIRE can be risky because it relies entirely on future market growth - which is impossible to predict. If returns are lower than expected, your Coast FIRE plans could be derailed.

Because of this risk, it's important to consider different growth rate scenarios and build your plan around a more conservative estimate.

Same $2M target:

Lower anticipated returns mean you require a larger portfolio size.

Adjusting for Inflation

Coast FIRE math already assumes inflation indirectly.

The growth rate you use should be real return (after inflation).

Typical long-term assumptions:

• Market return: ~10%
• Inflation: ~3%
• Real return: ~7%
• Conservative real return: ~6%

Using real return keeps your future retirement spending in today's dollars.

This simplifies planning and makes it easier to understand your Coast FIRE number.

A Practical Example

Let’s say:

• You’re 30 years old
• Want $70k retirement spending
• Plan to retire at 65
• Use 4% withdrawal
• Assume 7% real return

Step 1:

$70,000 ÷ 0.04 = $1,750,000 retirement goal

Step 2:

35 years until retirement converted to growth factor ≈ 10.7

$1,750,000 ÷ 10.7 ≈ $163,000 (your Coast FIRE number)

If you reach $163k invested, you can stop saving for retirement forever. Anything you choose to save after that is optional.

What Coast FIRE Means

Often times, we feel that only the already wealthy can achieve financial independence.

Coast FIRE shows us however that you can secure your future freedom relatively easily with disciplined saving and investing.

However, an important principle of Investing especially applies here:

Reaching Coast FIRE is exponentially harder as you get closer to your retirement age.

Once you reach Coast FIRE:

• You have more freedom with your income as further saving is optional.
• You can take more risks in your career.
• You can focus on other life goals without financial stress.

How to Reach Coast FIRE Faster

The key to reaching Coast FIRE is aggressive saving and investing early.

To increase your savings you have two main levers:

1. Increase your income
2. Decrease your expenses

Doing either of these will increase the margin in your budget that can be invested towards Coast FIRE.

Additionally, the earlier you start investing, the more time your money has to grow. Reaching Coast FIRE for a 25 year old will be significantly easier than for a 45 year old.

Key take-away: Save as aggressively as you can, as early as you can.

Consider alternatives

Coast FIRE isn't the only path. Depending on your goals, you might prefer:

• Barista FIRE: Keep working part-time while your investments grow, giving you income flexibility
• Lean FIRE: Fully retire earlier with a lower-spending lifestyle

Common Mistakes

Using unrealistic returns

• Be conservative with your growth rate assumptions. Coast FIRE relies entirely on future growth - which is impossible to predict. Because of this, you should be extra cautious with your estimates.

Forgetting lifestyle changes

• Your retirement spending may be very different from your current spending. Make sure to account for this in your calculations.

Stopping all investing

• Coast FIRE means you can stop saving for retirement, but continuing to invest can help you reach other financial goals. Just because you reach Coast FIRE doesn't mean you should stop investing altogether.

Ignoring taxes and accounts

• Different investment accounts have different tax implications. Make sure to consider how taxes will affect your investments and withdrawals in retirement.

Written by

Caleb Elliott

Software engineer and personal finance writer documenting my own FIRE journey. I save ~50% of my income and build the tools I wish existed to help others reach financial independence faster.

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