The Coast FIRE Calculator (Pro) answers one question precisely: can you stop saving for retirement today and still hit your number? Coast FIRE is the moment your invested portfolio is large enough that compound growth alone — with no further contributions — will reach your full financial-independence number by the age you want to retire. After that point you only have to earn enough to cover your current expenses. You are no longer saving for the future; you are coasting into it.
This Pro version goes well beyond a single result. It works in real, inflation-adjusted returns so every figure stays in today’s money, draws a year-by-year projection chart comparing the path where you keep contributing against the path where you coast on what you already have, tells you your personal Coast FIRE number at every age until retirement, pinpoints the exact age you cross the coast line if you keep saving, and lets you export the entire projection table to CSV for a spreadsheet. It is built for anyone weighing whether to throttle back contributions, downshift to a lower-stress job, or take a career break without derailing retirement.
How it works
You give it five things: your current age and target retirement age, how much you already have invested, an expected nominal return, an inflation rate, the annual spend you want in retirement, and your safe withdrawal rate. From there the maths runs in three steps. First it finds your FIRE number — desired annual spend divided by your withdrawal rate (spend ÷ 0.04 for the classic 4% rule). Second it converts your nominal return into a real return with the Fisher equation so growth is measured in today’s purchasing power. Third it discounts the FIRE number back to the present at that real return to get your Coast FIRE number today. If your current pot already exceeds it, you are coasting.
The chart then simulates every year between now and retirement. The blue line grows your pot with both compounding and your monthly contributions; the green line grows only your current pot with no new money; the amber dashed line is the Coast FIRE target at each age. Where the green line rises to meet the amber line, you can stop contributing entirely.
Example
Suppose you are 32, want to retire at 60, already have £75,000 invested, save £600/month, expect a 7% nominal return with 2.5% inflation, and want £40,000/year in retirement at a 4% withdrawal rate.
- FIRE number: £1,000,000 (40,000 ÷ 0.04)
- Real return used: about 4.39%/yr
- Coast FIRE number today: roughly £300,000
You are not coasting yet — you are short of that £300,000 today — but at £600/month you cross your Coast FIRE line in your mid-forties, well before age 60. From that age onward you could stop contributing and let the pot drift to your million.
| Age | Keep contributing | Coast on today’s pot |
|---|---|---|
| 32 | £75,000 | £75,000 |
| 42 | ~£230,000 | ~£115,000 |
| 52 | ~£475,000 | ~£177,000 |
| 60 | ~£760,000 | ~£250,000 |
Every figure is calculated in your browser — nothing is uploaded or stored on a server.