FIRE Calculator

What this calculator tells you

FIRE stands for financial independence, retire early. The idea is to save a large share of income so that an investment portfolio can eventually pay for living costs, allowing an early exit from full-time work. This calculator shows the portfolio size needed for your annual spending at a chosen withdrawal rate, and the number of years it would take to reach that size at your savings rate.

The result depends on three assumptions: the spending you need, the withdrawal rate you consider sustainable, and the return your portfolio earns while you save. Changing any one of them changes the answer, so the calculator is best used to test ranges rather than a single figure.

How the target is worked out

The portfolio target equals annual spending divided by the withdrawal rate. A withdrawal rate of 4% means the portfolio needs to be 25 times annual spending. The years to reach the target are found by repeatedly adding savings and investment growth each year until the portfolio reaches the target.

A worked example

Suppose you need 40,000 a year and use a 4% withdrawal rate. The target is 40,000 divided by 0.04, which is 1,000,000. If you have 100,000 invested and add 30,000 a year, growing at 5% a year, the portfolio reaches the target in roughly seventeen years. The exact time depends on the timing of contributions and returns, which is what the calculator works out.

Why the withdrawal rate is the critical assumption

A lower withdrawal rate needs a larger portfolio but lasts longer, while a higher rate reaches the target sooner but leaves less margin if markets fall early in retirement. The 4% figure is a common reference from historical studies of US markets, not a guarantee, and results differ by country, market conditions and length of retirement. A retirement that may last forty years or more needs a more cautious rate than a shorter one.

Limits of the calculation

The calculator uses a steady return and steady spending, neither of which happens in practice. A bad market in the early years of retirement can do lasting damage, and healthcare, housing or family costs can rise. Taxes on withdrawals and on investment income are not included, and neither are pensions or other income that may start later.

Early retirement also means a longer period without earnings and possibly without employer benefits, such as health cover or retirement contributions. These are real costs and should be planned for separately.

What early retirement changes

Retiring early shifts costs that an employer would otherwise cover, such as health insurance and retirement contributions, onto your own budget. Model these separately. Spending also often changes over a long retirement, with some costs rising early and others falling later, so a flat spending figure may not match your actual needs.

Using the result

Use the target and the years as a planning tool, and test a lower withdrawal rate, a higher spending figure and a lower return to see how sensitive the plan is. Build in a margin for unexpected costs, and review the plan regularly, because a plan that works on paper can fail if the assumptions do not hold.

Testing the plan with lower returns

Run the calculation with a return lower than the one you expect, such as two percentage points less, and see how the target and the years change. A plan that still reaches a reasonable target under a lower return is more robust than one that depends on the best case. The same applies to spending: a plan that works only if spending stays unusually low is fragile, so include a margin for the costs that rise over time.