Coast FIRE by Age: Your Exact Number at 25, 30, 35, 40, and 45

What Is Coast FIRE and How Does the Formula Work

Coast FIRE is the point where your existing investments will compound to your full retirement number on their own, assuming a 7% real annual return. You stop mandatory contributions and 'coast' — you still work, but only to cover current living expenses, not future ones.

The formula is straightforward:

**Coast FIRE Number = Retirement Target ÷ (1 + r)^n**

Where r is your expected real return rate and n is the number of years until retirement. Your retirement target itself follows the 4% rule: **Annual Spending × 25**. At $60,000/year in retirement, that's a $1,500,000 target.

So if you're 30 with 35 years until age 65: $1,500,000 ÷ (1.07)^35 = $1,500,000 ÷ 10.68 = **~$140,500**. That's your coast FIRE number at 30 for a $60k/year retirement. Hit that and you can stop investing entirely and still retire on schedule.

Two variables dominate this calculation more than anything else: your age today (which sets n) and your target retirement spending (which sets the numerator). Your assumed return rate matters too — we use 7% real return as the consensus long-run equity estimate, consistent with historical U.S. market data from 1926–2024. Change that to 5% and your required coast number nearly doubles.

Coast FIRE Numbers by Age: The Exact Targets for a $50k Retirement

Here are the precise coast FIRE numbers assuming a $50,000/year retirement income need (a $1,250,000 total target using the 4% rule), 7% real annual return, and retirement at age 65.

**Age 25 → 40 years of compounding → Coast FIRE number: ~$172,000** $1,250,000 ÷ (1.07)^40 = $1,250,000 ÷ 14.97 = $83,500 ... wait — that's the math. At 7% real over 40 years, $83,500 becomes $1.25M. So your coast number at 25 is **$83,500**.

Let's run all five:

- **Age 25** (40 years): $1,250,000 ÷ 14.97 = **$83,500** - **Age 30** (35 years): $1,250,000 ÷ 10.68 = **$117,000** - **Age 35** (30 years): $1,250,000 ÷ 7.61 = **$164,300** - **Age 40** (25 years): $1,250,000 ÷ 5.43 = **$230,200** - **Age 45** (20 years): $1,250,000 ÷ 3.87 = **$322,900**

Every five years you wait, your required coast number grows by roughly 40%. That's not a linear penalty — it's exponential. The investor who hits $83,500 by age 25 is in a fundamentally different position than the one who needs $322,900 by 45 to achieve the same outcome.

For a $70,000/year retirement ($1,750,000 target), multiply each figure above by 1.4. For $40,000/year ($1,000,000 target), multiply by 0.8. The ratios stay constant — only the scale shifts.

How to Use the Coast FIRE Calculator: Step-by-Step

Our coast FIRE calculator takes your specific inputs and returns your exact coast number in under 60 seconds. Here's what each field means and why it matters.

**Step 1 — Current Age and Retirement Age.** The gap between these two numbers is n in our formula. Most people default to 65, but if you're targeting early retirement at 55, your n shrinks and your coast number rises sharply.

**Step 2 — Current Savings.** Enter your total invested assets — 401(k), IRA, taxable brokerage, HSA if you'll use it for retirement. Do not include emergency funds, home equity, or car values. These are not compounding investment assets.

**Step 3 — Annual Retirement Spending.** This is the single most important input. A $10,000 difference in annual spending changes your coast number by $250,000. Be honest: use your current after-tax spending as a baseline, then adjust for expected lifestyle changes.

**Step 4 — Expected Return Rate.** We default to 7% real (inflation-adjusted). If your portfolio is more conservative (40% bonds), consider 5–5.5%. If you're 100% equities and comfortable with volatility, 7% is defensible based on long-run Vanguard and JP Morgan Asset Management return forecasts.

**Step 5 — Read Your Results.** The calculator shows three things: your coast FIRE number, whether you've already hit it, and how many years at your current savings rate until you do. If you've already crossed the line, the tool will tell you — and that's the moment most people realize they've been over-saving out of anxiety rather than necessity.

Three Worked Examples Across Different Income Levels

**Example 1 — The 28-Year-Old Software Engineer** Maria is 28, has $95,000 invested, earns $130,000, and expects to spend $65,000/year in retirement. Her target: $65,000 × 25 = $1,625,000. Years to 65: 37. Coast number: $1,625,000 ÷ (1.07)^37 = $1,625,000 ÷ 12.22 = **$133,000**. Maria has $95,000 and needs $133,000. She's 71% of the way there. At her current $2,500/month savings rate, she hits coast FIRE in approximately **14 months**.

**Example 2 — The 38-Year-Old Teacher Couple** James and Priya are both 38, have $180,000 combined, and project $80,000/year in retirement spending. Target: $2,000,000. Years to 65: 27. Coast number: $2,000,000 ÷ (1.07)^27 = $2,000,000 ÷ 6.21 = **$322,000**. They're at $180,000 — 56% of their coast target. Saving $3,000/month combined, they reach coast FIRE in roughly **3.5 years**, at age 41–42. After that, they only need to cover current expenses from income — retirement takes care of itself.

**Example 3 — The 45-Year-Old Career-Changer** Derek is 45, has $310,000 saved, and plans to spend $55,000/year in retirement. Target: $1,375,000. Years to 65: 20. Coast number: $1,375,000 ÷ (1.07)^20 = $1,375,000 ÷ 3.87 = **$355,400**. Derek is $45,400 short. At $1,500/month savings, he closes that gap in about **2.5 years**. The message: even starting seriously at 45, coast FIRE is achievable — it just requires a leaner retirement target or a few more years of saving.

Run your own version of these scenarios at our coast FIRE calculator.

The Inputs That Move Your Coast FIRE Number the Most

Not all variables are created equal. Here's how sensitive your coast number is to each input, ranked by impact:

**1. Retirement Spending (highest impact).** Every $1,000 change in annual retirement spending shifts your coast number by $25,000 (since target = spending × 25, and the coast discount is applied to the whole target). Cutting $500/month from your projected retirement budget saves you $150,000 in required coast savings. This is the lever most people ignore.

**2. Current Age / Years to Retirement.** As shown in our by-age table above, waiting five years raises your required coast number by roughly 35–40%. This is pure compounding math — time is not recoverable.

**3. Assumed Return Rate.** Moving from 7% to 6% real return increases your coast number by approximately 25–30% depending on your time horizon. Moving from 7% to 5% nearly doubles it over long horizons. This is why portfolio construction matters even after you hit coast FIRE — a conservative allocation extends the timeline or raises the bar.

**4. Retirement Age.** Pushing retirement from 65 to 60 shortens your compounding window by 5 years and simultaneously increases your retirement target (you need to fund more years under the 4% rule, or use a 3.5% withdrawal rate for safety). A 60-year-old retirement effectively raises your coast number by 40–60% compared to age 65, depending on your spending level.

The bottom line: before you try to save more, optimize your retirement spending estimate and make sure your equity allocation is appropriate for the time horizon.

What Happens After You Hit Your Coast FIRE Number

Reaching your coast FIRE number is a real inflection point — but it's not the end of financial planning, it's a transition. Here's what the post-coast period actually looks like in practice.

You still need earned income to cover current expenses. Coast FIRE doesn't mean you can quit your job — it means you no longer *need* to direct savings toward retirement. Many coast FIRE achievers use this milestone to take lower-paying but more fulfilling work, reduce hours, or switch careers without the pressure of maximizing compensation.

Sequence of returns risk still applies. If your portfolio drops 40% in year one of coasting, you may need to resume contributions temporarily. A good rule: mentally add a 20% buffer to your coast number before declaring yourself done. Instead of $133,000, Maria from Example 1 might target $160,000 before fully backing off contributions.

You should also keep a full financial plan updated. Coast FIRE is one variable in a broader picture that includes Social Security timing, healthcare costs before Medicare (age 65), potential inheritance, and tax-advantaged account strategy. Build your complete picture at finai.app/plan to see how coast FIRE fits into your full retirement projection.

When Coast FIRE Doesn't Work: Three Scenarios to Reconsider

Coast FIRE is a powerful concept, but it breaks down in specific situations you need to know about before relying on it.

**1. You're heavily allocated to low-return assets.** If your 'investments' are primarily in a money market account, stable value fund, or long-term bonds, 7% real return is not realistic. Coast math at 7% with a portfolio returning 3% real means your actual coast number is roughly 2.5× higher. Check your allocations before trusting the formula.

**2. Your retirement spending estimate is too low.** Healthcare is the most underestimated retirement expense. Fidelity's 2025 estimate puts average healthcare costs for a 65-year-old couple at $330,000 in today's dollars over retirement. If your retirement spending number doesn't account for this, your coast target is likely understated by $50,000–$100,000.

**3. You're planning to retire before 55.** Below 55, you face penalties for accessing most tax-advantaged accounts early (with some exceptions like Roth contribution basis and Rule 72(t) SEPP distributions). The coast FIRE formula is mathematically sound, but the *access* layer requires separate planning. A 40-year-old coasting toward a 50-year retirement needs a taxable brokerage bridge strategy for years 50–59.5.

If any of these scenarios apply to you, get a personalized read on your situation by building your free plan — it takes about 5 minutes and factors in your specific account structure, tax situation, and timeline.

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