Coast FIRE Calculator Guide 2026: When Your Savings Can Coast to Retirement

Coast FIRE is a popular financial independence milestone that sits between traditional FIRE (Financial Independence, Retire Early) and conventional retirement planning. It represents the point where you have saved enough that compound growth alone will grow your pot to your retirement target — meaning you no longer need to save aggressively, though you still need to work to cover living expenses. This guide explains what Coast FIRE is, how to calculate your number, and how to use it in your financial planning.

What is Coast FIRE?

Coast FIRE is the financial milestone where your existing savings, left to grow through compound interest at a reasonable rate of return, will reach your desired retirement fund by your target retirement age — without any further contributions. At this point, you only need to earn enough to cover your current living expenses. You no longer need to save for retirement because your existing pot will do the work for you.

The concept was popularised by the FIRE (Financial Independence, Retire Early) community as a more achievable middle ground between traditional retirement and full FIRE. Full FIRE requires saving 25× your annual expenses (the 4% rule), while Coast FIRE requires much less because you are relying on compound growth over time rather than having the full amount saved upfront.

Reaching Coast FIRE provides significant psychological relief. You know that if you simply keep working and earning enough to live on, your retirement is effectively funded. This opens up career options — you might take a lower-paying but more fulfilling job, reduce your working hours, or take a sabbatical without worrying about retirement savings.

How to Calculate Your Coast FIRE Number

Calculating your Coast FIRE number involves working backwards from your target retirement fund. Here is the formula:

For example, if you want £1,000,000 at age 65, you are currently 35 (30 years until retirement), and you expect a 7% annual return:

This means that if you have £131,367 saved today at age 35, and it grows at 7% per year, it will reach £1,000,000 by age 65 — without any additional contributions. You would still need to work to cover your living expenses, but your retirement is effectively funded.

Coast FIRE vs Regular FIRE

Understanding the distinction between Coast FIRE and regular FIRE helps set realistic financial goals:

Feature	Coast FIRE	Regular FIRE
Savings target	Lower (compound growth does the rest)	25× annual expenses (full amount)
Work required	Yes, to cover living expenses	No (can retire completely)
Savings rate	Can reduce to minimum	Must maintain high savings rate
Time to achieve	Typically 5–15 years	Typically 15–25 years
Risk	Lower (still earning income)	Higher (no income buffer)
Lifestyle impact	Moderate (career flexibility)	Significant (must save aggressively)

Coast FIRE is often considered a stepping stone towards full FIRE. Many people reach Coast FIRE first, then gradually increase their savings rate as their income grows, eventually reaching full FIRE. Others are happy to remain at Coast FIRE, enjoying the freedom to choose work without the pressure of aggressive saving.

How to Use the Calculator

Our Coast FIRE calculator makes it easy to determine your personal Coast FIRE number. Simply enter:

• Current age: Your age today.
• Target retirement age: When you want to reach your retirement fund.
• Target retirement fund: How much you need at retirement (use 25× annual expenses as a guide).
• Expected annual return: The growth rate of your investments (7% is a reasonable long-term average for equities).
• Current savings: How much you already have saved for retirement.

The calculator will tell you whether you have already reached Coast FIRE, how far away you are, and when you are projected to reach it. It also shows the impact of different return rates and retirement ages.

Coast FIRE Examples

Here are some real-world examples to illustrate how Coast FIRE works:

Example 1: Early Starter (Age 25)

Sarah is 25, wants to retire at 65, and needs £500,000. With a 7% annual return, her Coast FIRE number is £500,000 / (1.07)^40 = £66,782. If she has already saved £70,000 by age 25, she has reached Coast FIRE. She can now reduce her savings rate and focus on experiences rather than aggressive accumulation.

Example 2: Mid-Career (Age 40)

James is 40, wants to retire at 60, and needs £800,000. With a 7% return, his Coast FIRE number is £800,000 / (1.07)^20 = £206,502. He currently has £150,000 saved. He needs an additional £56,502 to reach Coast FIRE. At his current savings rate, he will reach Coast FIRE in approximately 5 years.

Example 3: Late Starter (Age 45)

Priya is 45, wants to retire at 65, and needs £600,000. With a 7% return, her Coast FIRE number is £600,000 / (1.07)^20 = £154,887. She has £100,000 saved. She needs £54,888 more, which she can accumulate in approximately 3 years at her current savings rate.

Investment Strategy

Your investment strategy plays a crucial role in reaching and maintaining Coast FIRE. Since you are relying on compound growth, your allocation needs to be growth-oriented:

• Young investors (20s–30s): Consider 90–100% equities, diversified through low-cost index funds. You have decades for compound growth to work.
• Mid-career (40s): Gradually shift towards 70–80% equities, 20–30% bonds. Maintain growth but start reducing volatility.
• Approaching retirement (50s+): Move towards 60/40 or 50/50 allocation. Protect your accumulated wealth while still capturing some growth.

The key is keeping costs low. High fees erode compound growth significantly over decades. Choose low-cost index funds or ETFs with expense ratios below 0.2%. Consider using tax-efficient accounts like ISAs and pensions to maximise after-tax returns.

Remember that Coast FIRE is not a guarantee — market returns are unpredictable. Build in a buffer by aiming for a slightly higher Coast FIRE number than the minimum, and maintain the ability to increase contributions if needed.