Financial independence starts with your spending.

Work through a complete example

Suppose you spend 3,000 a month and expect 1,000 a month of reliable income once retirement starts. The portfolio must cover the remaining 2,000 a month, or 24,000 a year.

Use one currency throughout. These targets do not include tax unless your spending budget does. If the other income starts later, model the years before it starts separately; subtracting it immediately would understate the assets you need.

Separate the saving years from the withdrawal years

During accumulation, contributions and investment growth build the portfolio. During retirement, withdrawals and the sequence of returns determine how long it lasts. A smooth growth line is useful for comparing savings plans, but it cannot tell you whether a retirement portfolio survives an early market fall.

1. Use the FIRE planner for the path to your target.
2. Compare lower returns, higher spending and a lower withdrawal rate.
3. Use the historical test or simulation to examine withdrawals after retirement.

What changes the target most?

At a 4% withdrawal rate, each permanent 100 per month of spending requires 30,000 more in portfolio assets: 100 × 12 ÷ 0.04. Reducing recurring spending can both lower that target and free money to invest, provided the reduction is sustainable.

A temporary expense needs a different treatment. A loan payment ending in five years should not automatically be multiplied by 25 as though it lasts forever. Separate long-term spending, temporary costs and one-off purchases before choosing a target.

Understand what “coasting” buys you

Coast FIRE asks when your existing investments might grow to a retirement target without more retirement contributions. You still need income for present living expenses. This can help compare a lower-paid job or shorter hours, but the calculation depends heavily on how many years remain and the return assumption.

Check the assumptions before acting

• Inflation: keep future cash amounts and today’s purchasing power separate. See a worked example.
• Taxes and fees: include the spending or return drag relevant to your accounts.
• Time horizon: a long early retirement needs more years of withdrawals.
• Uneven returns: a fall early in retirement can have a different outcome from the same fall later.
• Flexibility: distinguish spending you could reduce from essential bills.

Sources and further reading

The 4% discussion refers to Bengen’s historical withdrawal study. For saving mechanics, see the SEC’s compound-interest calculator. Our methodology explains the precise conventions used here. These examples are educational scenarios, not a recommendation to retire or buy a particular investment.