Coast FIRE means having enough invested so that, even without further contributions, your portfolio grows to your FIRE number by retirement.
The key formula: Coast FIRE Number = FIRE Target / (1 + r)^years to retirement.
Your FIRE target is typically 25× your annual expenses, based on the 4% safe withdrawal rule.
Use this calculator before making any financial commitment that depends on this type of calculation. Running the numbers in advance lets you evaluate options without the pressure of a live negotiation or decision deadline.
Many financial calculation errors stem from omitting ancillary costs: fees, taxes, insurance, or maintenance. The headline figure (interest rate, monthly payment) is rarely the complete cost of a financial product.
An employee receives a counter-offer from another employer: a £4,000 salary increase but no pension contribution versus the current role's lower salary with 8% employer pension. Running both through the finance calculator shows the true net financial value of each offer.
Coast FIRE means your current savings will grow to your retirement goal without additional contributions.
Regular FIRE requires accumulating the full amount. Coast FIRE only requires hitting a lower threshold today.
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