Most people think of retirement savings as a 40-year obligation that ends when they stop working. Coast FIRE flips that idea. Reach a specific savings number early enough and compound interest does the rest — your portfolio grows to your retirement target on its own. You can stop contributing entirely.
The Core Idea in One Sentence
If you have $197,000 saved at age 35 and retire at 65, that $197k grows to approximately $1.5 million at 7% annual return — without a single additional contribution. $197k is the Coast FIRE number for someone who needs $60,000/year in retirement. Once you hit it, you've "coasted" to the finish line.
Calculate Your Coast FIRE Number
How Is the Coast Number Calculated?
Step 1: Find your FI target (25× annual retirement spending — the 4% rule). If you need $60,000/year: $60,000 × 25 = $1,500,000. Step 2: Discount that target back to today using your expected return rate and years until retirement. Coast Number = $1,500,000 ÷ (1.07)^30 = $197,000. That's the math. The earlier you hit it, the less you need — because time does the work.
- •A 25-year-old needs less than a 35-year-old to coast to the same retirement — time compounds more.
- •A 30-year-old who maxes their Roth IRA ($7,000/year) for just 5 years might already be at their Coast number.
- •The Coast number shrinks dramatically with each year you save aggressively.
What Life Looks Like After Coast FIRE
After hitting Coast FIRE, you still need to earn enough to cover living expenses — you just don't need to save for retirement. This is where it gets interesting. Many people use this milestone to leave high-stress corporate jobs, go part-time, switch careers to something more meaningful, start a side business, or travel for a year. As long as you cover today's bills, future you is taken care of.
Coast FIRE pairs perfectly with geographic arbitrage. Hit your Coast number in a high-income city, then move somewhere with a lower cost of living where your income need drops significantly. Your retirement savings keep compounding while your current expenses drop.
Coast FIRE vs Lean FIRE vs Fat FIRE
Lean FIRE: retire now on a tight budget (spending under $40k/year). Fat FIRE: retire now with a comfortable lifestyle (spending $80k+/year). Coast FIRE: you're not done working, but your retirement is already funded. It's not the finish line — it's the moment you take your foot off the gas.
Most people who reach Coast FIRE in their 30s report that the psychological effect is transformative — knowing you'll be fine at retirement removes an enormous amount of financial anxiety, even if you're years away from actually retiring.