One family, one set of numbers
Two people aged 35, spending $60,000 a year, with $200,000 invested and saving $30,000 a year, assuming a 5% real return and a 4% withdrawal rate, with a normal retirement at 62. Their full FIRE number is $60,000 ÷ 0.04 = $1,500,000, which at their saving arrives in 20 years, at 55. Every figure below uses these inputs, and both calculators on this site will reproduce them.
Coast FIRE for this family
The coast number is the full number discounted back over the 27 years to 62: $1,500,000 ÷ 1.05²⁷ = $401,772. They have $200,000, so they are $201,772 short. Saving $30,000 a year, they cross the line in 9 years, at 44: from then on, if they never saved another dollar, the portfolio would grow to $1,500,000 by 62 on its own. Their jobs from 44 only have to pay the $60,000 they live on.
Barista FIRE for this family
Suppose one of them could earn $25,000 a year after tax from part-time work they would enjoy. The portfolio then only has to pay $60,000 − $25,000 = $35,000 a year, so the Barista number is $35,000 ÷ 0.04 = $875,000, reached in 13 years at 48. That is 7 years earlier than full FIRE. At 3.5% instead of 4% the Barista number is $1,000,000, which takes 15 years.
Side by side
Coast arrives in 9 years and asks for a job that pays $60,000 until 62. Barista arrives in 13 years and asks for $25,000 of part-time work for as long as the portfolio needs the help. Full FIRE arrives in 20 years and asks for nothing. Coast is the earliest change of pressure; Barista is the earliest change of hours; full FIRE is the only one that needs no work at all.
Who each suits
Coast FIRE suits people who like their field but not the pace, or who want to take a lower-paid job they care about without hurting retirement. It also suits anyone whose income may fall later, since the saving is front-loaded. Barista FIRE suits people with a clear part-time option, a low and steady budget, and the stomach for watching the portfolio through a downturn while drawing on it.
The risks the simple maths leaves out
Both plans lean on a steady 5% real return for decades; at 3% the coast number for this family rises to $675,284 and the timelines stretch. Barista FIRE adds sequence risk, since withdrawals start young, and depends on the part-time work existing in ten years. Both assume spending stays at $60,000 in real terms through children, houses and health. The Coast FIRE and Barista FIRE calculators let you test every one of those assumptions with your own numbers.
A way to decide
Ask two questions. Is there work you would happily do for twenty more years if it only had to pay the bills? If yes, Coast FIRE is the natural plan and it arrives first. Is there part-time work you are sure of, in a place where leaving a full-time job does not cost you health cover? If yes, Barista FIRE lets you cut your hours years earlier. If the answer to both is no, the full number is the target, and the FIRE calculator shows the fastest route to it: the savings rate.