Coast FIRE calculator: how much do you need saved to stop saving?
The coast FIRE formula with a worked example, a coast FIRE number table by age, what most calculators leave out (inflation, Social Security, taxes, couples) and a free calculator.
October 11, 2026 · 7 min read
Coast FIRE is the point where the money you've already invested will grow into a full retirement fund on its own, even if you never add another dollar. After that, your paycheck only has to cover today's bills. It's a popular goal because it changes the question from "how do I save millions?" to "how much do I need by 35 or 40?". Here's the formula, a table by age and the things most coast FIRE calculators leave out.
Short answer: coast FIRE number = FIRE number ÷ (1 + real return)years to retirement. If you'll spend $50,000 a year in retirement, your FIRE number at a 4% withdrawal rate is $1,250,000. At a 5% real (after-inflation) return, a 30-year-old retiring at 65 reaches coast FIRE with about $227,000 invested.
The coast FIRE formula, step by step
- FIRE number = yearly spending in retirement ÷ safe withdrawal rate. At 4%, that's spending × 25: $50,000 × 25 = $1,250,000.
- Years to grow = retirement age − your age. 65 − 30 = 35 years.
- Real return = (1 + expected return) ÷ (1 + inflation) − 1. A 7% return with 2.5% inflation is about 4.4% real. Using the real return keeps every number in today's dollars.
- Coast FIRE number = FIRE number ÷ (1 + real return)years. $1,250,000 ÷ 1.0535 ≈ $226,600 at 5% real, or about $277,900 at 4.4% real.
If your invested balance today is at or above that number, you've reached coast FIRE. If not, the gap tells you how much more to invest, and how long it takes at your current savings rate.
Coast FIRE number by age
For $50,000 a year of retirement spending ($1.25 million FIRE number), retiring at 65:
| Your age | Years to grow | Coast number at 5% real | At 4.4% real (7% return, 2.5% inflation) |
|---|---|---|---|
| 25 | 40 | $177,600 | $224,100 |
| 30 | 35 | $226,600 | $277,900 |
| 35 | 30 | $289,200 | $344,400 |
| 40 | 25 | $369,100 | $427,000 |
| 45 | 20 | $471,100 | $529,300 |
| 50 | 15 | $601,300 | $656,200 |
The pattern is the whole point of coast FIRE: every five years you wait, the number you need rises by roughly a quarter, because there's less time left for compounding to do the work. Spending $40,000 instead of $50,000 cuts every number in the table by 20%.
What most coast FIRE calculators leave out
- Inflation. A calculator that grows your money at 7% but compares it with today's spending overstates how close you are. Use a real return, or inflate the spending too.
- Social Security and pensions. Income you'll get anyway lowers the spending your portfolio has to cover. If Social Security will pay $20,000 a year, the portfolio only funds $30,000 of a $50,000 budget, and the FIRE number drops from $1.25 million to $750,000.
- Couples. Run it on combined spending and combined invested assets, and use the younger partner's years to retirement if you plan to stop together.
- Taxes. Money in a traditional 401(k) or IRA is taxed when you withdraw it. If most of your savings are pre-tax, aim for a higher spending figure to cover the tax.
- Sequence risk. Coasting assumes an average return. A bad decade near the start of retirement hurts more than the average suggests, so many people keep a margin of 10 to 20% above their coast number.
Coast FIRE vs other kinds of FIRE
- Full FIRE: you have the whole FIRE number now and can stop working.
- Coast FIRE: you have enough invested to reach the FIRE number by a normal retirement age; you work only to cover current costs.
- Barista FIRE: you've retired from your main career and part-time income covers the gap between withdrawals and spending.
- Lean and fat FIRE: the same math, on a small or a generous spending figure.
What reaching coast FIRE actually changes
You still need income: the plan only works if you don't withdraw from the investments before retirement. What changes is the pressure. You could take a lower-paying job you like better, go part-time, take a sabbatical or build a side business, as long as it covers your current bills. That's why coast FIRE and side income planning go together; for ideas that don't need upfront money, read 12 ways to boost your monthly income and our guide to the best side hustle app.
Run your own numbers
The free coast FIRE calculator at monthlyincomebooster.com uses real returns, so the answer is in today's dollars, and shows how many years of saving it takes to get there. The same calculator is built into the Monthly Income Booster app for Android (listed on Google Play as Coast FIRE & Side Hustle Ideas), with no account and no bank linking. Keeping regular bills under control is the other half of the plan; the free Bill Organizer app tracks them with due-date reminders.
This article is general education, not financial advice. Returns are not guaranteed; check your own figures with a qualified adviser before changing how you save.
Frequently asked questions
How do you calculate coast FIRE?
Divide your FIRE number (yearly retirement spending ÷ withdrawal rate, e.g. × 25 at 4%) by (1 + real return) raised to the number of years until retirement. If your invested balance is at least that amount, you've reached coast FIRE.
What is a good coast FIRE number at 30?
For $50,000 a year of retirement spending and retirement at 65, about $227,000 at a 5% real return, or about $278,000 at 4.4% real (7% return minus 2.5% inflation).
Does coast FIRE include Social Security?
It should. Subtract the Social Security or pension income you expect from your retirement spending before working out the FIRE number. $20,000 a year of Social Security lowers a $1.25 million FIRE number to $750,000.
What return should I use in a coast FIRE calculator?
A real (after-inflation) return keeps the answer in today's dollars. Many people use 4 to 5% real for a stock-heavy portfolio; a lower figure gives a safer target.
What is the difference between coast FIRE and barista FIRE?
With coast FIRE your investments grow into a full retirement fund by a normal retirement age while you work to pay current bills. With barista FIRE you have already left your career and part-time income fills the gap between withdrawals and spending.
