The FIRE 4% Rule Rigidity: Why My Beancount Data Shows I Need 3.4% (And You Probably Have Your Own Number)

General
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I need to share something that’s been bothering me about the FIRE community’s obsession with the 4% rule.

As a bookkeeper working with 20+ small business clients, I see this pattern all the time: “Industry averages” mean nothing for YOUR specific business. A restaurant with 8% margins isn’t failing just because the industry average is 15%. A construction company with 22% margins isn’t guaranteed success.

The same logic applies to personal finance. The 4% safe withdrawal rate is an average, not a prescription.

Why I Started Questioning 4%

I’ve been using Beancount for 3 years now to track my personal finances alongside my business bookkeeping. When I first heard about FIRE, everyone was preaching “save 25x your expenses, withdraw 4% per year, you’re set for life.”

But my bookkeeper brain immediately asked: “Which expenses? Under what conditions? With what income sources?”

So I did what I do for clients - I ran the numbers on MY actual data.

What My Beancount Data Revealed

Using Beancount’s query language, I pulled three years of personal expense data and discovered:

My spending varies by 18% year-over-year. One year I spent $38K (everything went smoothly). Next year $45K (car died, A/C replacement, dental work). The year after that? $41K. Generic FIRE calculators assume I spend exactly the same amount every year. My ledger says that’s fantasy.

I have irregular income that changes the math. I run a bookkeeping business - some months are feast (tax season), others are famine. I can’t predict annual income with precision, which means I need a bigger safety buffer than someone with a stable W-2 salary.

My retirement timeline is aggressive. I’m targeting retirement at 50, which could mean 40+ years of portfolio withdrawals. According to updated Trinity Study research, safe withdrawal rates for 40-50 year retirements drop to 3.25-3.5%, not 4%.

My Personalized Safe Withdrawal Rate

After modeling my specific situation in Beancount, factoring in:

  • Expense volatility (18% year-over-year variation)
  • Irregular income (no pension, no guaranteed Social Security at full amount)
  • Long retirement horizon (40+ years)
  • Limited ability to reduce fixed costs (healthcare, housing)

My number: 3.4%

That means I need to save about 29.4x annual expenses instead of 25x. That’s 18% more savings. That might mean working 2-3 additional years.

And honestly? I’m fine with that. I’d rather work a few extra years than run out of money at 75.

A Client Example That Drives This Home

I have a restaurant client who was following “industry standard food cost percentages” (28-32%). He was bleeding cash and couldn’t figure out why.

When we dug into HIS specific data in Beancount, we discovered his actual food costs were 38% because:

  • Higher-end ingredients for his target market
  • Smaller volume = less supplier discounts
  • Higher waste due to daily specials

The “industry average” was useless for his specific restaurant. He needed to work with HIS numbers, not someone else’s benchmark.

The same applies to FIRE planning.

What Makes YOUR Number Different From 4%?

Think about these factors:

Expense Flexibility:

  • High fixed costs (mortgage, healthcare) = need lower withdrawal rate
  • Mostly discretionary spending (travel, hobbies) = can handle higher rate

Income Sources:

  • Just portfolio withdrawals = more conservative rate needed
  • Rental income, pension, part-time work = can sustain higher rate

Retirement Timeline:

  • Retiring at 35 for 60 years = need 3.0-3.25% (research confirms)
  • Retiring at 65 for 30 years = 4% is probably fine

Portfolio Allocation:

  • Heavy stocks (75%+) = can potentially handle higher rate with more volatility
  • Conservative bonds (50%+) = need lower rate with less growth potential

Spending Volatility:

  • Consistent year-to-year = 4% might work
  • High variation = need buffer for bad years

How to Calculate YOUR Number Using Beancount

If you’ve been tracking expenses in Beancount for at least 2-3 years, here’s what I recommend:

  1. Pull annual expense data (I use this query):
SELECT year, sum(convert(position, 'USD')) as total
WHERE account ~ '^Expenses:'
  AND NOT account ~ 'Expenses:Taxes'
GROUP BY year
ORDER BY year

  1. Calculate your spending volatility - how much does it vary?

  2. Factor in your specific circumstances - retirement length, income sources, expense flexibility

  3. Stress test - what if the market crashes in your first year of retirement?

  4. Arrive at YOUR personalized safe withdrawal rate

For me, transparency is everything (it’s literally my job). Beancount gives us the raw data to make informed decisions instead of blindly following rules of thumb.

Questions for the Community

I’d love to hear from others tracking FIRE progress in Beancount:

  1. Have you calculated a personalized safe withdrawal rate? What did you find?

  2. What factors make your situation different from the “average” 4% retiree?

  3. How often do you recalculate? Quarterly? Annually? After major life changes?

  4. Am I being too conservative with 3.4%? Or are others also finding they need lower rates for early retirement?

One thing I’ve learned in bookkeeping: the numbers don’t lie, but averages can be misleading. I’d rather plan conservatively based on MY data than optimistically based on someone else’s research from 1998.

What do you think?