Coast FIRE: When You Can Stop Saving and Let Compounding Finish

Coast FIRE is calculated by discounting your full FIRE number backward by the years until you want to retire. Formula: Coast FIRE Number = FIRE Number ÷ (1 + real return rate)^years until retirement. At 7% real return, a 35-year-old targeting $1.5M at age 65 needs only $197,000 invested today — that $197K grows to $1.5M over 30 years of pure compounding, with no additional contributions. From that point, they can reduce savings to zero, take a less stressful job, start a business, or otherwise restructure their life. Coast FIRE is compelling because it arrives much earlier than traditional FI — often 10-15 years sooner — and requires only that you can cover current living expenses from current income.

Coast FIRE (sometimes spelled 'Coast FI') emerged from the early-2010s FIRE blogosphere as a variant of the full-FI concept. The term captures the specific insight that compounding does most of the work in long retirement plans — a dollar invested at 30 is worth approximately 8× a dollar invested at 60 if returns follow historical patterns. Retirees choosing the Coast path often frame it as 'Work-Optional' rather than 'Retired Early', since they continue earning income (just stop saving toward retirement). The Mad Fientist blog and ChooseFI podcast have been particularly influential in popularizing the concept.

The 7% real return assumption is load-bearing and debatable. At 5% real (some modern forecasts, including current high-CAPE implied returns), the Coast FIRE number grows dramatically. Our 35-year-old example at 5% real needs $347K instead of $197K — 75% more. Historical periods have produced annualized real returns below 5% for extended stretches (1966-1982 was ~1-2% real for US equities). Second: 'retirement' is treated as a binary — you stop working at a specific age — but in practice many Coast FIRE adherents keep working into their late 60s, which changes the math substantially. Third: Coast FIRE doesn't account for spending drift. If your current $60K budget grows to $80K by the time you 'retire', you need a bigger base than originally calculated. Fourth: healthcare costs before Medicare (for early Coast FIRE adopters who fully stop working in their 50s) are a common underestimate.

• “Coast FIRE formula” — FI/RE community (Mad Fientist, ChooseFI), 2015-present
• “7% real long-run equity return” — Shiller data, Jeremy Siegel 'Stocks for the Long Run'
• “Current high-CAPE implies lower forward returns” — Pfau, Asness et al.

• Mr. Money Mustache, 'The Shockingly Simple Math Behind Early Retirement' (2012) (accessed 2026-04-17)
• Bogleheads Wiki — Safe Withdrawal Rates (accessed 2026-04-17)
• Bengen (1994), 'Determining Withdrawal Rates Using Historical Data', Journal of Financial Planning (accessed 2026-04-17)

Last verified: 2026-04-17