The Problem With Static Plans
Every FI plan is built on assumptions. You assume a certain income trajectory, a certain spending level, a certain rate of return. And when you first run the numbers, those assumptions feel solid — they reflect your life as it is right now.
But life moves. You get a raise, or you don't. You have a kid. You relocate somewhere cheaper. The market drops 30% in your first year of retirement. Your company's stock doubles, or gets cut in half.
The plan itself doesn't break — your confidence in it does. You start wondering: how fragile is this? If one thing changes, does the whole timeline shift by five years? Or barely at all?
The question isn't whether your assumptions will be wrong. It's how much it matters when they are.
That's what scenario analysis answers. Not “what will happen,” but “what happens to my plan if this changes?”
Testing Your Plan, Not Predicting the Future
Scenario analysis isn't about forecasting. Nobody can predict what the market will do next year, or whether you'll still be at the same job in five years. The point is different: you take your existing plan and ask what if one assumption changes?
What if you spent 20% less? What if the market returned 2% less than expected? What if you held your company stock instead of selling? Each question isolates one variable and shows you how sensitive your FI date is to that change.
Some changes barely move the needle. Others shift your timeline by years. Knowing which is which changes how you think about your plan — and how much energy you spend worrying about things that turn out not to matter.
What MoneyOnFIRE Tests For You
When you run your plan, the engine automatically generates scenarios across five dimensions. Each one re-runs the full simulation with modified assumptions and shows the updated FI date and FIRE number alongside your baseline.
Expenses
What if you reduced your spending by 10%, 20%, or 30%? This one is powerful because it has a double effect: you save more during your working years and you need a smaller portfolio to sustain lower expenses in retirement. The combined impact is often larger than people expect.
Income
What if your salary growth accelerates? Higher income means a larger investable surplus each month, which compounds over time. This scenario helps you quantify how much a raise or promotion actually moves your FI date — sometimes it's less than you'd think, depending on where you are in your journey.
RSU: Keep or Sell
By default, the engine assumes you sell RSUs on vest and invest the proceeds in diversified index funds. But what if you held your company stock? This scenario models outcomes across a range of stock performance assumptions — from poor (-20%) to strong (+20%) — so you can see the concentration risk alongside the potential upside.
Market Returns
How sensitive is your plan to overall market performance? The engine tests conservative, baseline, and optimistic return assumptions. If a 2% drop in annual returns pushes your FI date out by eight years, that's worth knowing. If it only moves it by one, you can worry less about short-term market noise.
Withdrawal Rate (SWR)
The safe withdrawal rate determines how much you draw from your portfolio each year in retirement. A lower SWR means you need a larger portfolio but have a greater safety margin. A higher SWR gets you to FI faster but with more risk. This scenario shows you the tradeoff in concrete terms: years of additional work versus percentage points of safety.
What This Looks Like in Practice
Marcus, 34
Product manager, $140K salary, targeting FI at 50
$6,200
50
Marcus worries about market risk. He reads headlines about corrections and wonders if a bad decade could derail his plan entirely. So he looks at his scenarios.
Market returns: conservative
If annual returns come in 2% below the baseline assumption:
FI at 53
3 years later
Expenses: 20% reduction
If Marcus cuts monthly expenses from $6,200 to $4,960:
FI at 45
5 years earlier
The insight: Marcus was focused on the thing he can't control (market returns) while underestimating the thing he can (spending). A modest expense reduction — $1,240 per month — has nearly twice the impact of a pessimistic market, and it moves the timeline in the right direction. That's not obvious without running both scenarios.
What Scenarios Don't Do
It's worth being clear about what this feature is and isn't.
The What If scenarios are sensitivity analyses — the engine varies one dimension at a time and shows you how your plan responds. They're not a freeform “build your own scenario” tool. You can't combine “lower expenses AND higher income” into a single scenario view.
If you want to model a completely different life path — a new city, a career change, a second child — the right approach is to save a separate plan with different inputs and compare the results. Each plan gets its own full simulation and its own set of scenarios.
The value of the built-in scenarios is that they're automatic. You don't have to think about what to test or how to set it up. The engine identifies the levers that matter and shows you the range of outcomes. It's a starting point for understanding your plan's sensitivity, not the final word on every possible future.
Getting the Most From Your Scenarios
Three steps
- Run your base plan first. The scenarios are most useful when you have a realistic baseline. Get your income, expenses, and assets right before looking at the What If tab.
- Look for asymmetry. Which lever moves your FI date the most? For some people it's expenses, for others it's income or market returns. Your plan's sensitivity profile is unique to your situation.
- Act on what you find. If a scenario looks compelling — say, a 20% expense reduction accelerates FI by five years — update your actual plan inputs to reflect the change and see the full impact across your entire financial picture.
The goal isn't to find the “perfect” scenario. It's to understand which assumptions your plan depends on most, so you can focus your energy where it actually matters.
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