The "Front-Loaded" Retirement: Understanding Coast FIRE
Most people save for retirement linearly: they save 10% of their paycheck every month from age 22 to age 65. Coast FIRE turns this model on its head. It is based on the mathematical power of front-loading your investments.
The concept is simple: There exists a specific net worth number (your "Coast Number") where your portfolio has enough momentum to grow into your full retirement goal without you adding another penny. Once you hit this number, you have "coasted." You don't need to retire yet, but you no longer need to save for retirement. This effectively gives you a 20-50% raise for the rest of your working life.
The Power of Time
Compound interest favors the early bird. A dollar invested at age 20 is worth roughly 10x more at age 60 than a dollar invested at age 50.
Example
If you invest $100,000 at age 30 and never save again, at a 7% return, it will grow to $761,000 by age 60.
If you wait until age 50 to start, you would need to save $5,000/month for 10 years to reach that same number.
Coast vs. Traditional FIRE
Traditional FIRE is about racing to the finish line as fast as possible to quit working entirely. Coast FIRE is about slowing down once you've built a safety net.
- Traditional FIRE: High Savings Rate (50%+) until net worth = 25x expenses.
- Coast FIRE: High Savings Rate only until net worth = Coast Number. Then, Savings Rate drops to 0%.
Coast FIRE allows you to spend 100% of your paycheck on life today—travel, hobbies, or working a lower-paying "passion job."
The "Coast FIRE" Lifestyle
Reaching Coast FIRE doesn't mean you stop working; it means you stop working for the future. This shift changes your relationship with your career.
Career Risk Taking
Since you don't need to save, you can take a pay cut to join a startup, start your own business, or switch to a non-profit. The pressure to maximize income disappears.
Lifestyle Inflation
Usually "lifestyle creep" is bad. In Coast FIRE, it's allowed. You can upgrade your car or take nicer vacations using the money that used to go into your 401(k).
Sabbaticals
Because your retirement is secure, you can afford to take 6-12 months off work. While you aren't contributing during that time, your nest egg keeps growing in the background.
The Danger of "Drifting"
The math of Coast FIRE relies heavily on assumptions. You are assuming a certain rate of return (e.g., 7% real) for 20-30 years. If the market underperforms (e.g., returns only 4%), your Coast Number won't grow enough to cover your retirement.
The Fix: Coast FIRE is not a "set it and forget it" strategy. You must re-evaluate annually. If the market has a bad decade, you may need to resume contributing or delay retirement by a few years. However, having a large base invested early gives you more flexibility to adjust than someone starting from zero.
The "Rule of 72" Shortcut
Want to do the math in your head? The Rule of 72 states that you divide 72 by your interest rate to see how many years it takes for your money to double.
- At 7% return, money doubles every ~10 years.
- At 10% return, money doubles every ~7 years.
If you are 30 and want to retire at 60 (30 years), your money has time to double 3 times (at 7%). That means $100k becomes $200k, then $400k, then $800k. If you need $800k to retire, your Coast Number at age 30 is just $100k.