Coast FIRE Calculator

What is Coast FIRE?

Coast FIRE is the moment your invested savings become large enough that you no longer need to add another dollar to retire on time. From that point on, ordinary compound growth carries the portfolio the rest of the way. You still have to work to cover today's living expenses, but you are free to stop retirement saving, to "coast" into retirement. It is the lowest, most achievable milestone on the FIRE (Financial Independence, Retire Early) ladder, which is exactly why it is such a motivating number to calculate.

The appeal is psychological as much as financial. Hitting your Coast FIRE number means the hardest part, building the base, is done. A 32-year-old who has coasted can switch to a lower-paying but more meaningful job, take a career break, or simply stop stressing about their 401(k), and still expect a fully funded retirement at 60.

The formula this calculator uses

Two steps. First, find the full nest egg you will need at retirement using the safe-withdrawal-rate rule:

target corpus = annual spending ÷ withdrawal rate

Then discount that target back to today using your expected real (after inflation) return over the years until retirement:

coast number = target corpus ÷ (1 + real return)^(retirement age − current age)

If your current investments are at or above the coast number, you are already coasting. If not, the calculator simulates your balance forward year by year, compounding and adding your monthly contributions, until it catches the (gradually rising) coast target, which tells you the age at which you can stop.

Two worked examples

Example 1, a 30-year-old planning to retire at 60

Suppose you expect to spend $40,000 a year in retirement and use a 4% withdrawal rate. Your target corpus is $40,000 ÷ 0.04 = $1,000,000. With a 7% real return and 30 years to compound, the money grows roughly 7.6×, so your Coast FIRE number today is about $1,000,000 ÷ 7.6 ≈ $131,000. Invest ~$131k now and, even if you never save another cent, you should reach $1M by 60.

Example 2, not there yet, still contributing

Same targets, but you have $50,000 invested and add $1,000 a month, aiming to retire at 65. You are below the coast number today, so the calculator projects your balance forward. Around age 35 your portfolio overtakes that year's coast target, meaning after roughly five more years of saving you could stop contributing entirely and still glide to your $1M goal.

When to use it

• Deciding whether you can downshift to a lower-stress or lower-paid job.
• Planning a sabbatical or extended career break without derailing retirement.
• Setting an early, motivating savings goal that feels reachable in your 30s.
• Sanity-checking whether you are "behind" or comfortably ahead of schedule.

Limitations to keep in mind

Coast FIRE rests on assumptions that will not hold perfectly. Real returns vary year to year, and a poor sequence of returns early on can leave you short even if the long-run average lands where you expected. The model also assumes you can cover all living costs without touching investments after you coast, if you can't, growth gets interrupted. Healthcare, taxes, and lifestyle inflation aren't captured here, and the 4% rule is a guideline, not a guarantee. Treat your coast number as a confidence-building checkpoint, revisit it every year or two, and keep a margin of safety rather than stopping contributions the instant you cross the line.