Full FIRE means your investments cover your life forever. Coast FIRE is the milestone before it: the day your invested balance is big enough that compounding alone finishes the job. You still work, but only to cover today's bills. Saving for retirement becomes optional.
Take someone who wants $40,000 a year in retirement. The classic rule of thumb says they need $1,000,000 invested (25 times spending). At age 30, targeting age 60 with a 7% return, the coast number is about $131,000. Cross that line and the math takes over: even if they never invest another dollar, the balance grows past the million by 60.
Most of the money in a retirement account comes from growth, not deposits - but only if the deposits happen early. Coast FIRE turns that into a concrete target with a date. Someone with $50,000 invested who adds $1,500 a month from age 30 reaches their coast point in about five years. Everything they save after that is buying an earlier or richer retirement, not a necessary one.
The 7% default is a long-run stock-market average, not a promise, and real returns arrive unevenly. The 25-times rule comes from research on historical US market data - it is a planning target, not a guarantee. Inflation, taxes and fees all take a cut. Revisit the numbers once a year rather than setting them in stone.
Estimates only. Markets do not move in straight lines, and this is not financial advice.
Figured Out