FIRE Calculators

The one formula underneath all of them

Annual spending divided by your safe withdrawal rate. At 4%, that is simply 25 times what you spend in a year. Lean, Regular and Fat FIRE are not different maths — they are different numbers put into the same equation.

What separates the variants is when the portfolio has to be finished and whether you are still earning:

• Coast FIRE — the portfolio is untouched and still compounding; you work only to cover today's costs. A 30-year-old retiring at 60 on $40,000 a year needs about $318,862 today, against a $1,000,000 FIRE number.
• Coast FIRE for couples — one household, one number, with the age gap handled properly. The horizon is the later of two retirement dates, which is why a partner eight years younger cuts the wait from 19.3 years to 10.7.
• Barista FIRE — you are already drawing on the portfolio, and part-time work covers the rest. At a 4% rate, every $1 of part-time income removes $25 from the target.
• Fat FIRE — the same formula on an unconstrained lifestyle. Every extra $10,000 of annual spending adds $250,000 to the number.

The assumption that decides everything

Coast FIRE in particular lives or dies on the return you assume, and the sensitivity is larger than most people expect. For a 30-year-old retiring at 60 on $40,000 a year, the Coast FIRE number is $561,614 at a 5% return and $182,946 at 9% — a threefold swing on one input nobody can know in advance.

Which is why the honest reading of any of these numbers is a range, not a threshold. Run yours at a cautious rate as well as an optimistic one and treat the gap as your margin of error.

Which one you actually need

The two levers, and which is bigger

Only two things move any FIRE date: how much you save, and how much you will spend. Spending is the stronger lever, because it appears on both sides of the equation — money not spent is money saved, and a lower target needs less capital.

In the Fat FIRE model, a household spending $60,000 finishes at 55 where one spending $100,000 finishes at 64. Nine years, from the spending figure alone. Every extra $10,000 of annual spending adds $250,000 to the target at a 4% withdrawal rate.

What none of these model

• Sequence-of-returns risk. Growth is applied smoothly. A poor first decade of withdrawals damages a portfolio far more than the same decade later.
• Healthcare before Medicare. For US early retirees this is frequently the binding constraint rather than the portfolio, and it must sit inside your spending figure.
• Social Security or pensions. Any guaranteed income reduces what the portfolio must cover — subtract it from spending before entering.
• Whether you will still want it. Every model here assumes you keep choosing the plan for decades.