This FIRE number calculator estimates the portfolio size linked to a chosen annual spending level and withdrawal-rate assumption. It is a planning illustration, not a retirement plan and not financial advice. The result can change materially if spending, investment returns, fees, inflation or withdrawal assumptions change. Investments can fall as well as rise, past performance is not a reliable guide to future results and capital is at risk.
What this calculator assumes
- The FIRE number is annual spending divided by the withdrawal-rate assumption.
- Investment growth is estimated using the return entered after deducting annual fees.
- Returns are smoothed for illustration and do not model real market volatility.
- Tax, inflation, pensions and changing spending are not fully modelled.
- Investment values can go down as well as up and capital is at risk.
How the FIRE number is estimated
The calculator divides target annual spending by the withdrawal-rate assumption entered. For example, a lower withdrawal rate creates a larger estimated portfolio target, while a higher withdrawal rate creates a smaller one. That does not make either number automatically safe. Withdrawal rates are assumptions, not guarantees, and real retirement planning needs more detail than a single calculator can provide.
How the time estimate works
The time-to-target estimate starts with the current portfolio, adds the monthly contribution entered and applies the assumed annual return after fees. This is deliberately simple. It does not model tax, pension rules, changing contributions, market crashes, inflation shocks or changes to spending. The most useful way to read it is as a sensitivity test: change the assumptions and notice how quickly the answer moves.
Why this is not a retirement plan
A FIRE number can be useful for orientation, but it is not a complete answer. Real financial independence planning can involve pensions, ISAs, tax wrappers, state pension entitlement, mortgage costs, cash buffers, sequence-of-returns risk and changing spending over time. This calculator helps with the first-pass maths, then the assumptions need proper review.
Useful official sources
FAQs
Is the FIRE number a guaranteed retirement target?
No. It is an estimate based on the annual spending and withdrawal-rate assumptions entered. Different assumptions can produce very different targets.
What withdrawal rate should I use?
The calculator cannot tell you the right withdrawal rate. It lets you test assumptions, but sustainable withdrawals depend on market returns, inflation, fees, tax, spending flexibility and personal circumstances.
Why does time to target change so much?
Small changes to returns, contributions, fees or spending can compound over long periods. That is why the output should be treated as an illustration rather than a forecast.