Quand pourriez-vous vraiment partir ?

Figuring out when you can actually retire combines everything else on this site into one answer: given what you've already saved, what you keep contributing, and what you'll spend, what age does your invested portfolio cross your FIRE number (using the 4%-rule-style math from the FIRE number calculator)? It's the same underlying compounding and withdrawal-rate logic, solved for a target date rather than a target dollar amount.

How it's calculated

The calculation first determines your FIRE number (annual spending ÷ withdrawal rate, e.g., ×25 at 4%), then projects your current invested savings forward with monthly contributions and an assumed real rate of return until the projected balance crosses that number — the age at which that happens is your retirement age. It's the inverse operation of coast FIRE, which instead asks what balance today needs zero further contributions to reach the same target.

Why it matters

Small changes compound into large timeline shifts: increasing monthly contributions, even modestly, or trimming planned retirement spending both pull the crossing point earlier, often by more years than intuition suggests, because of how compounding and the 25x multiplier interact (a spending cut reduces the target and frees up more money to contribute, a double effect).

Common pitfalls

Using an overly optimistic return assumption (ignoring historical volatility, sequence-of-returns risk, fees, and taxes) makes the projected date look earlier than it will likely turn out to be in practice. It's also easy to forget that planned retirement spending, healthcare costs before an age like 65 (see the healthcare gap calculator), and inflation over a multi-decade projection all need to be estimated in today's dollars consistently, or the crossing-point age will be distorted by mixing nominal and real figures.