Coast FIRE at 30 vs 40 vs 50: How the Numbers Change
Starting at 30, you need $93,663 invested to coast to $1,000,000 by age 65 at a 7% real return. Wait until 50 and the price jumps to $362,446. Same target, same return, wildly different ticket. Plug your own age into the Coast FIRE calculator and you'll see exactly where you land. (The 7% is a real return — here's why that distinction matters.)
The short answer
Time does the heavy lifting in Coast FIRE, and it charges by the decade. With a $1,000,000 target at age 65 and a 7% real return, a 30-year-old needs $93,663 today, a 40-year-old needs $184,249, and a 50-year-old needs $362,446. Each ten-year delay almost doubles the amount you must already have invested. Turning 35 soon? The age-35 checkpoint breaks down that exact milestone.
Nothing else changes between those three people. Same destination, same market return, same rule of adding nothing more after today. The only variable is how many years of compounding are left, and compounding is ruthless about lost years. A dollar at 30 gets 35 years to grow. A dollar at 50 gets 15. That gap is the entire story of this page.
The numbers at 30, 40, and 50
Here are the three numbers side by side. Each assumes a $1,000,000 target at 65, a 7% real return, and zero further contributions after today:
| Age today | Years left to grow | Needed today |
|---|---|---|
| 30 | 35 | $93,663 |
| 40 | 25 | $184,249 |
| 50 | 15 | $362,446 |
Read the jump from 40 to 50 carefully. The 50-year-old needs nearly double what the 40-year-old needs, and close to four times the 30-year-old's number. And these figures assume the money stays fully invested the whole way. Cash sitting idle coasts to nothing.
Get the number for your exact age
The table uses round ages. The calculator uses yours, plus your real target and what you've already saved.
Run the Coast FIRE calculator →Why waiting doubles the price
At 7%, money doubles roughly every ten years. That's the whole mechanism.
The old rule of 72 says it plainly: divide 72 by your return and you get the doubling time. 72 divided by 7 is about 10.3 years, so a portfolio left alone doubles roughly once a decade. Start at 30 and your money gets three and a half doublings before 65. Start at 40 and it gets two and a half. Start at 50, one and a half.
Every doubling you miss has to come out of your pocket instead. Miss one doubling, and you must save roughly twice as much to land in the same place. Miss two, roughly four times. The market was perfectly willing to do that work for free. It just needed the years.
What this means if you're starting late
Starting at 45 or 50 doesn't close the door. It just changes which levers matter.
First, save aggressively right now. Coast FIRE assumes you add nothing after today, but nothing stops you from contributing. Every dollar you add still compounds for 15 or 20 years, which is plenty of time to matter. Second, consider a later retirement date. Each extra year both lengthens the growth period and keeps the target unchanged in today's dollars, so the amount needed today falls faster than you'd expect.
Third, look at your spending target. The full target is 25 times your planned annual spending, so cutting $4,000 a year off that target removes $100,000 from the finish line before discounting. Trimming lifestyle expectations beats stuffing more cash into the account, almost every time. And if the concept itself is new to you, start with our guide on what Coast FIRE is and how it works before running your numbers.
See what your starting age costs you
Change one input, your age, and watch the target move. It's the fastest way to feel what a decade is worth.
Try the calculator →The bottom line
The $1,000,000 destination never changes. What changes is who pays for it: time, or you. At 30, time pays for more than 90% of it. At 50, you're covering far more of the bill yourself. Whatever your age, run your own figures through the Coast FIRE calculator today. The cheapest day to start was a decade ago. The second cheapest is now.