Free Coast FIRE Calculator (+ Guide)

What is a Coast FIRE calculator?

A Coast FIRE calculator works out how much you need invested now so that, without adding another dollar, it grows to your FIRE number by the age you retire.

Past that point, you only need to earn what you spend.

How it works

The calculator works it out on your device, and your numbers stay there.

FIRE and Coast FIRE numbers

Your FIRE number is the pot that pays a year of spending at your withdrawal rate. At 4%, $40,000 a year needs $1,000,000.

Your Coast FIRE number is that pot brought back to today. At 30, with 35 years to go at 5% a year, $1,000,000 ÷ 1.05 to the 35th power is about $181,290.

That growth is compound interest, interest on your money and on the interest it already earned.

Why the 4% withdrawal rate

The 4% default comes from William Bengen's 1994 study, and the FIRE calculator explains what it tested.

A lower rate, like 3.5%, gives a bigger and safer target, and you can type any rate you like.

A worked example

Here's the example the calculator loads: age 30, retiring at 65, $40,000 a year of spending, 4% withdrawals, 5% a year after inflation, $100,000 invested and $1,000 a month saved.

The FIRE number is $1,000,000 and the Coast FIRE number today is about $181,290, so you're about $81,290 short.

Saving $1,000 a month, you'd reach Coast FIRE at about 38. From then on, growth alone carries you to $1,000,000 at 65.

Mistakes to avoid

These are the slips that come up most.

• Typing a return before inflation, which makes the target look smaller than it is
• Forgetting the tax on the money you'll take out
• Counting money you'll spend before retirement, like a home deposit
• Stopping the day you reach the number, with no room for a bad decade

Who is the Coast FIRE calculator for?

It's for anyone who wants to know when saving for retirement is done, and these tools help around it.

• FIRE calculator – for your full FIRE number and date
• Retirement calculator – for a regular retirement plan
• Compound interest calculator – for growth at any rate
• 401(k) calculator – for your workplace plan

Find your number, then decide what the years after it are for.