Retirement · Coast FIRE
Coast FIRE calculator.
Your coast number is what you need invested now so that growth alone reaches your financial-independence number by retirement age. Enter your plan and see how far you are.
Coast number = FI number ÷ (1 + real return)years to retirement. With a $1,000,000 FI number, 35 years to go and a 5% real return, the coast number is $181,290. Once your invested balance passes it, growth alone can reach $1,000,000 by 65 without another contribution.
Inputs
Result
Enter your numbers.
How the coast number works
Coast FIRE is a way of splitting retirement saving in two. First pick the amount you want at retirement (the FI number: yearly spending divided by your withdrawal rate). Then work backward: the coast number is that amount discounted at your expected real return for the years left. Wikipedia describes CoastFIRE as saving aggressively early, until the portfolio is projected to grow to a sufficient level through compound interest alone, after which further contributions may be reduced or stopped.
Worked example. Age 30, retiring at 65, spending $40,000 a year at a 4% withdrawal rate: FI number = 40,000 ÷ 0.04 = $1,000,000. Growth factor over 35 years at 5% real = 1.0535 = 5.516. Coast number = 1,000,000 ÷ 5.516 = $181,290. With $100,000 invested you are $81,290 short; left alone, $100,000 grows to $551,602 by 65. Adding $10,000 at the end of each year, your balance passes the coast number for your age in year 11, at age 41.
The coast number only covers the retirement end. You still have to pay your living costs from earnings until retirement, and returns are not guaranteed. The tool uses a single steady real return, so it ignores bad years, taxes and fees.
Frequently asked questions
What is a coast number?
It is the amount you need invested today so that, with no further contributions, growth at your assumed real return brings you to your FI number by retirement age. It is the FI number divided by (1 + return) raised to the years remaining.
Does Coast FIRE mean I can stop working?
No. It means you can stop saving for retirement, not that your income can stop. You still need earnings to cover your living costs until the money is needed.
Which return should I use?
Use a real return, meaning after inflation, so every figure stays in today’s dollars. 5% real is a common planning assumption but is not guaranteed. Try 3% and 4% to see how sensitive the coast number is.
How is this different from the FIRE calculator?
The FIRE calculator finds when you can retire. This one is built around the coast question: how much do I need now, how does that number change with age, and when do my contributions reach it.
Sources
Checked
- Wikipedia: FIRE movement
- Mr. Money Mustache: The Shockingly Simple Math Behind Early Retirement (13 January 2012)
Runs entirely in your browser. Nothing you type is sent or stored. Formulas are standard arithmetic; assumptions such as returns are yours to set.
Not advice
Illustration only. Real returns vary year to year and are never guaranteed. Not financial, tax or investment advice.