The Method

Retirement isn't a number.
It's a structure with mass, tension, and noise.

Datum FI is the physics engine that resolves them into one honest Shape.

Every tool has a method. Most hide theirs.

Ours is the product itself — five acts you move through, five things the math does in response. The acronym is not a mnemonic. It is a sequence. Each letter is a physics primitive. Each act builds on the one before it. Together they form the only honest path from rough envelope to lived answer.

Reveal the Shape.

Every calculation begins with inputs. But the choice of which inputs matter — and how they are used — is already a methodology decision.

The Sketch takes five: your current age, your retirement age, your investable capital, your annual contributions, and your target annual spending. From these five it draws three simultaneous paths.

A conservative path — if returns compress and markets disappoint.
A baseline path — if markets behave near historical averages.
An upside path — if conditions lean your way.

These three paths form the envelope. The lower path becomes the Survival Floor. The upper path becomes the Structural Ceiling. The middle path is where your Datum is placed.

A single withdrawal rate cannot answer three structural questions simultaneously. The Sketch uses path-tuned rates:

• The Survival Floor rate is reduced. It asks what the conservative path can sustain under stress.
• The Structural Ceiling rate is elevated. It asks what the upside path could support under favorable conditions.
• The Datum rate sits on the baseline path. It asks what your inputs honestly project.

The 4% rule applies one rate universally — derived from a 1994 study of US returns from 1926 to 1976, then extended to every retiree regardless of path, time, or context. That is a heuristic. The Sketch uses three rates because the Shape has three structural questions, and collapsing them into one answer destroys the information that makes the Shape useful.

Once the envelope is drawn and your Datum is placed, the relationship between them produces a structural reading. The Sketch resolves this in five states.

ABUNDANT — Your target sits below the Survival Floor. The conservative path already supports more than you're asking. The Shape has capacity you haven't decided what to do with yet.

GROUNDED — Your target sits near the lower boundary. The Survival Floor holds it; the space above is your margin. Whether you preserve it or test it is your decision.

EXPANSIVE — Your target sits inside a wide Shape with room in both directions. The question isn't whether the Shape holds — it's which edge is worth testing first.

STRETCHED — Your target is near the Structural Ceiling. The Shape carries it, but the upper paths are doing the work. Less margin means less tolerance for stress or delay.

OVEREXTENDED — Your target is above the Structural Ceiling. No modeled path reaches this lifestyle at current inputs. This is the most useful state the Sketch can produce: it tells you precisely where the gap is and which levers could close it.

These are positions, not judgments. The Shape tells you what is structurally true.

Define the Mass.

The Sketch draws the envelope using broad-stroke assumptions. Architecture replaces them with your actual structure.

Studio treats your retirement as a building you're drafting. Accounts become rooms. Plumbing carries cashflow. HVAC sets the climate. Each room has a different tax treatment, a different set of rules for when you can access it, and a different role in the sequence of withdrawals. A taxable brokerage account is not the same room as a traditional 401(k). A Roth IRA is not the same room as an HSA. The architecture of your financial life is the floor plan of these rooms — and the order in which you move through them determines how long the building holds.

Studio maps this architecture across four account types: taxable, tax-deferred, Roth, and health savings. For each, it models the tax treatment on contributions, growth, and distributions. It sequences withdrawals to minimize drag and extend the life of the portfolio. It layers in Social Security timing — when to claim, how the benefit interacts with other income — and any pension or structured income source.

Liabilities are modeled as loads the architecture must carry before the Shape can fully express itself. A mortgage, a structured obligation, a debt-servicing requirement — each changes the effective spending capacity of every year it's present. Architecture does not ignore them. It places them on the floor plan as fixed loads and builds the model around them.

Apply the Pressure.

A structure that has never been stressed is not a structure. It is a drawing.

Tension applies real pressure to the architecture — running it through the market conditions that will actually try to break it, and measuring where it holds, where it bends, and where it fails.

Studio models tension across four return regimes:

• Historical anchors the model to long-run behavior. The baseline against which everything else is measured.
• Optimistic tests the upper capacity under favorable returns.
• Cautious compresses the model toward the conservative path. How the structure behaves when markets underdeliver.
• Custom Matrix lets you enter your own return triplet. Your view of expected returns, volatility, inflation. The architecture is tested against your assumptions, not someone else's.

Beyond regimes, the engine runs a stress battery of named historical events: the 1929 Depression, the 1970s stagflation, the 2000–2008 Lost Decade. These are not scenarios in the colloquial sense. They are structural tests. Each one asks a precise question: under this regime, does the architecture produce a Shape that holds your Datum? If it does, what margin exists? If it doesn't, which room in the floor plan fails first?

Structure the Noise.

The most dangerous thing a retirement model can do is pretend that uncertainty is manageable with a single number.

It isn't. The future is not a line. It is a distribution — an enormous space of possible outcomes, each with its own sequence of returns, its own inflation path, its own timing of market stress. A deterministic model picks three points in that distribution and calls them the answer. That is useful. It is the right tool for drawing the first outline.

But the architecture you've built — the rooms, the sequencing, the tax treatment, the Social Security timing, the liability loads — deserves to be tested against the full distribution, not three points in it.

Studio runs 10,000 Monte Carlo paths through the complete architectural model. Each path is a different sequence of returns drawn from the defined tension regime. Each path runs the architecture from your current age through your full retirement timeline, measuring the Shape at every year along the way. Not one path. Not three. Ten thousand.

Four modeling lenses apply simultaneously:

• Parametric Log-Normal — draws from a statistical distribution calibrated to historical parameters.
• Empirical (1926–Present) — draws return sequences from actual historical data.
• CAPE Valuation Adjustment — modifies expected returns based on current equity valuations.
• Regime Bootstrap — conditions return sequences on the economic regime present at each point.

The output is not a line. It is a distribution — a cloud of 10,000 possible Shapes, each one honest about its assumptions. From that cloud, the boundaries emerge. This is not uncertainty eliminated. It is uncertainty structured. The noise becomes a surface you can read.

Resolve the Shape.

The Shape is not a separate product. It is the act where the engine resolves everything it has been given into the most honest answer it can produce.

Where the Sketch drew three deterministic lines, the Shape reveals a distribution-derived envelope:

• The Structural Ceiling is the percentile boundary above which the distribution does not reliably reach.
• The Survival Floor is the percentile boundary below which the distribution does not reliably support your Datum.
• Your Datum sits where your target spending intersects the distribution's behavior.

This is the moment of retirement. The architecture has been drafted. The tension has been applied. The noise has been structured. What remains is a measurement — the most complete one the methodology can produce.

They are not estimates of what might happen. They are measurements of what the engine, given everything it needs, believes is structurally true at the moment you stop working.

Live the Shape.

Most retirement tools stop at the finish line. They tell you whether you'll reach retirement. They go quiet on what happens during the thirty years that follow.

Datum FI does not go quiet.

The Lived Shape is the same Shape, re-measured continuously across the years you actually inhabit. The boundaries do not freeze at the moment of retirement. They breathe.

• In years when returns are strong, the Living Ceiling rises. The architecture has more capacity than the year-zero measurement projected. The room above the Datum grows.
• In years when markets stress, the Living Floor compresses. The conservative paths tighten. The room beneath the Datum shrinks.
• Your Datum Range — the band you are actually living inside — shifts with both. Some years carry more. Some carry less. The range within the Range.

This is the part of the methodology that almost every other retirement tool refuses to model. They give you a probability of success. They give you a target balance. They do not give you a structure that adjusts to the markets you actually experience, the spending you actually do, the conditions you actually face.

The Lived Shape does. It treats retirement not as a destination but as a thirty-year continuously-resolved instrument — one that responds to the markets in front of you and tells you, year by year, what the structure can carry.

Strong year → the Living Ceiling lifts. The math says: you can take more.
Stress year → the Living Floor holds. The math says: compress here, the structure still holds.
Quiet year → the Datum Range steadies. The math says: this is the band.

This is not optimization. It is honest year-by-year structural truth, delivered to you in the same Shape language you began with — but now responding to your actual life.