What Coast FIRE actually means
Coast FIRE is a specific and testable idea: the point at which your existing invested savings, left alone with no further contributions, would grow to fund your retirement by the time you reach it.
Reaching it does not mean stopping work. It means you no longer need to save for retirement. Your salary can go to living rather than to your future, and the pressure comes off. For many people that milestone arrives far earlier than full financial independence, and it is considerably more attainable.
How the calculation works
The maths is compound growth run backwards. Start from the pot you would need at retirement, discount it back to today at an assumed real rate of return, and you have your Coast FIRE number. Compare it with what you already have invested and you know whether you have reached it.
We also cover the neighbouring variants, because the terminology is a mess and people arrive looking for different things: Barista FIRE, where part-time work covers current costs, Lean FIRE on a reduced spending target, and Fat FIRE on a more comfortable one.
Assumptions, stated openly
Every projection of this kind rests on assumptions, and the honest thing is to name them. We use a real rate of return, meaning after inflation, so the figures are in today's money. We assume contributions stop entirely, which is the whole premise of Coast FIRE. We assume a withdrawal rate at retirement that you can adjust.
Change the return assumption by a single percentage point and the answer moves substantially. That is not a flaw in our calculator, it is the nature of forty year projections, and anyone presenting one as precise is overselling it. Run several scenarios rather than trusting one number.
Who publishes this site
CoastCalc is built and maintained by CJ Software Ltd, a UK software company that develops a small family of free, single-purpose calculators. We are a software business, not a firm of financial advisers, and we say so plainly because it matters when you decide how much weight to give a number on a screen.
The site is funded by advertising. Advertisers have no influence over the calculations, the guidance, or what we choose to write about.
Not financial advice
This is an educational model, not a recommendation. It cannot account for your pension arrangements, tax wrappers such as ISAs and SIPPs, State Pension entitlement, your actual risk tolerance, or what markets will do. Investments can fall as well as rise, and past returns tell you very little about future ones.
For decisions about your retirement, speak to a regulated financial adviser. MoneyHelper, the government-backed service, offers free impartial guidance and is a sensible first stop.