Your FI number is 25× your annual expenses — the portfolio that lets you live off investments forever.
At a 4% withdrawal rate, a
This calculator earns its keep at decision points: before accepting a loan, comparing investment platforms, or negotiating salary. The difference between the headline figure and the true cost or return is only visible with accurate arithmetic.
A frequent error is using annual rates where monthly rates are required (or vice versa). Simply dividing an annual rate by 12 is only an approximation — the correct conversion for compound calculations uses the (1 + r)^(1/12) − 1 formula.
A first-time buyer models three scenarios before making an offer: 10%, 15%, and 20% deposit on a £280,000 property. The calculator shows exactly how the monthly payment and total interest cost change with each deposit level, making the decision visible rather than speculative.
Your annual expenses × 25. This is the portfolio size that can sustain you forever at a 4% withdrawal rate.
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