Meet the FI Planner: The Complete Roadmap to Financial Independence

Alistair TeamJuly 7, 20267 min read
MicrotoolsFI plannerfinancial independenceFIREretirementmicrotools

A basic FIRE calculator takes your spending, multiplies by 25, and gives you a number. That's a start — but it's not a plan. Real financial independence involves pensions, Social Security, expenses that stop (like a mortgage or childcare), and scenarios you haven't modeled yet.

Alistair's FI Planner is the complete FI planning tool. It accounts for income sources you'll have in retirement, expenses that won't last forever, and what-if scenarios that change your timeline.

What Makes It Different

Income Sources in Retirement

Your FIRE number assumes your portfolio is your only income source. But most retirees have more than one:

  • Pension: A $2,000/month pension reduces your FI number by nearly $600,000 (using the 25x rule). That's real money most calculators ignore.
  • Social Security: Even a modest $2,000/month benefit at 67 reduces your required portfolio by hundreds of thousands. The tool factors this in — and lets you model claiming at different ages.
  • Part-time income: If you plan to earn $15,000/year from a passion project in "retirement," that reduces your required withdrawal.
  • Rental income: Net rental income offsets your expenses directly.

Time-Bound Expenses

Not every expense lasts forever:

  • Mortgage: A $2,000/month mortgage that's paid off in 12 years is fundamentally different from $2,000/month of lifetime expenses. The tool treats them differently.
  • Childcare: $1,500/month that ends in 8 years changes your FI timeline dramatically.
  • College tuition: 4 years of high expenses, then done.

By separating permanent and time-bound expenses, the tool gives you a much more accurate FI number than the 25x rule on total spending.

What-If Scenarios

The planner lets you test variations:

  • Delay retirement by 2 years: How much does waiting change your success probability?
  • Downsize the house: What if you sell the $600K house, buy a $350K condo, and bank $250K?
  • Inheritance or windfall: What does a $100K inheritance do to your timeline?
  • Higher/lower returns: What if the market returns 5% instead of 7%?

Real Numbers: A Complete FI Plan

  • Current age: 38
  • Net worth: $300,000
  • Annual expenses: $72,000 (but $24,000 is mortgage that ends in 20 years)
  • After-tax income: $130,000
  • Savings rate: 35%
  • Expected return: 7%
  • Pension at 65: $1,500/month
  • Social Security at 67: $2,200/month
  • Time-bound expense: Childcare at $1,200/month, ending in 10 years

Basic FIRE calculation: $72,000 × 25 = $1,800,000 FI number. At current savings ($45,500/year), reaches FI at ~54.

FI Planner calculation: The tool separates expenses, accounts for income sources, and recalculates:

  • Permanent expenses (excluding mortgage and childcare): $33,600/year
  • Time-bound expenses (mortgage + childcare): $38,400/year — but they end
  • Retirement income (pension + Social Security starting at 65 and 67): $3,700/month = $44,400/year

The tool models this year by year: the heavy expenses drop off at different times, the income sources kick in, and the portfolio drawdown adjusts. The effective FI number is significantly lower than $1.8M because:

  1. $44,400/year of retirement income covers the permanent $33,600 expenses — and then some
  2. The mortgage and childcare costs end before or during early retirement
  3. The portfolio only needs to bridge from retirement age to when Social Security and pension payments begin

Result: The effective FI number is roughly $1,100,000 — $700K less than the basic calculation. Reached at approximately age 47, not 54. Seven years earlier.

Why This Level of Detail Matters

A 25x calculation is directionally correct but can be wildly inaccurate for anyone with non-portfolio income sources or temporary expenses. It might tell you to work 7 extra years you don't need to — or worse, give you a false sense of security that you'll run out of money.

Alistair's FI Planner models the full picture: what you earn, what you spend, what stops, what starts, and what changes. Because financial independence isn't one number — it's a sequence of numbers over time.

That's what this microtool does. Build a real FI plan, not just a rule of thumb.