A cash flow model is not a prediction. It is a structured way of asking: if these things happen, what does the future look like? And what happens if they do not?
The first three guides in this series built a framework for understanding where money sits, how it is invested, and whether it will last. This guide introduces the tool that brings all of that together in a single, coherent picture: the cash flow model. It explains what the model is, what goes into it, how it is used, and what it actually tells you — before you see your own numbers.
A cash flow model is a year-by-year projection of your complete financial life. It takes everything that is known — all your income sources, all your assets, all your expenditure, all your liabilities — and projects it forward to a planning horizon, typically age 90, 95, or 100.
It is not a prediction. No model can predict the future. It is a structured framework for thinking about the future — one that makes every assumption explicit, allows those assumptions to be challenged, and shows what happens to the picture when any one of them changes.
The value of the cash flow model is not the central projection. It is the conversation that the projection enables. Seeing what your plan looks like if you retire two years earlier, if markets underperform for a decade, or if you need care at 82, gives you an understanding that no static questionnaire or investment report can produce.
Not a prediction. Every projection depends on assumptions. If the assumptions change, the projection changes. The model shows what would happen if — not what will happen.
Not a guarantee. A plan that looks sustainable under central assumptions can still be disrupted by events outside the model — unexpected health costs, family circumstances, policy changes.
Not a one-time exercise. A cash flow model is a living document. It should be updated as circumstances change and reviewed at meaningful intervals against the planning ratios it establishes.
A thinking tool. It structures complex, multi-variable financial decisions into a single picture that can be interrogated, challenged, and adjusted.
A communication tool. It translates abstract financial planning concepts into visible, concrete outcomes you can engage with and understand.
A scenario tool. It allows the question “what if” to be answered honestly — not by guessing, but by changing the assumption and seeing what happens to the plan.
A review tool. It establishes the baseline against which future progress is measured — using planning ratios rather than investment performance alone.
The charts and diagrams throughout this guide use illustrative shapes and patterns to show how the model works — not specific figures. Every cash flow model is different because every situation is different. The purpose here is to show the structure of the model: what it contains, how the variables interact, and what the output looks like — before you see your own numbers.
Many people encounter a cash flow model for the first time as a finished output — projections, charts, and conclusions already drawn. The model has already been built; the assumptions have already been set.
This guide reverses that sequence. It explains the model before you see it — so that when you do, you understand what every line means, what every assumption represents, and what questions you should be asking. Understanding the framework means you can engage with the process rather than simply receive its outputs.
Every model starts with a baseline: the best current picture of how things stand. Understanding what feeds the model — and why each input matters — is the first step.
A cash flow model is built from four categories of information: income, assets, expenditure, and liabilities. Each is a variable — change any one and the picture changes. The baseline is not a fixed document. It is the starting point from which every scenario and stress test is run.
Earned income — salary, self-employment income, rental income. When does it start, when does it stop, how might it change? Part-time work in early retirement is a significant variable.
State pension — when does it start (currently age 67), how much is it (full new state pension £11,502 for 2026/27), is it full or partial? State pension is the most valuable guaranteed income most people have.
Defined benefit pensions — when do they start, what do they pay, is there a spouse’s pension? A DB pension income is the closest thing to a personal annuity and transforms the risk profile of a plan.
Other guaranteed income — annuities purchased, rental income from property, trust distributions.
Pension pots — all defined contribution pensions, their current values, their wrapper structures, their investment risk levels, and their charges. Multiple pots from different employers need to be mapped onto a common risk framework (as covered in Guide 2).
ISAs and other investments — current values, wrapper structures, risk levels. The tax treatment on withdrawal is different from pensions and affects the net income the portfolio delivers.
Cash savings — emergency fund, short-term savings, Premium Bonds. These are not growth assets but they affect the sequencing of withdrawals.
Property — primary residence (typically not drawn upon but affects IHT position and care funding options), investment property (rental income and potential sale proceeds).
Essential expenditure — housing costs, utilities, food, transport, insurance. These need to be maintained regardless of market conditions.
Discretionary expenditure — holidays, leisure, dining, gifts. These can be reduced in poor market years — which is the source of the flexibility that significantly improves retirement sustainability.
One-off expenditure — home improvements, car replacement, helping children with deposits, significant travel. These appear as specific year events in the model.
Mortgage — outstanding balance, monthly payment, when it ends. A mortgage ending in retirement is a significant positive cash flow event that can reduce the required withdrawal rate substantially.
Other loans — personal loans, car finance, any other structured debt obligations.
Future known liabilities — school fees ending, a known future commitment that will cease.
IHT position — the estate value above the nil-rate band represents a future liability if estate planning is not addressed. This is a liability to the estate even if not to the individual’s cash flow.
A retirement income picture does not stay constant. It typically moves through distinct phases, each with different implications for how much needs to be drawn from the investment portfolio. The phasing is different for everyone — but the pattern below is common:
Every cash flow projection depends on assumptions. The single most important thing you can do with a financial plan is understand what those assumptions are — and challenge them.
A financial projection is only as good as its assumptions. An optimistic growth assumption can make a fragile plan look robust. An unrealistic inflation assumption can hide a real purchasing power problem. This chapter puts every assumption front and centre — not buried in small print, but visible, named, and available for discussion.
A cash flow model is only as good as the assumptions behind it — growth rate, inflation, charges, longevity, tax, and withdrawal sequencing all shape the result. These will be set out clearly in your own outcome report, along with how sensitive your plan is to each one. The right response to seeing a cash flow model is not to accept the projection. It is to ask about the assumptions. Some useful questions:
Investment performance is not a planning metric. It measures what markets did, not whether your plan is working. The planning ratios introduced here measure what matters: the health of the plan itself.
A portfolio that returned 8% last year when the market returned 10% is not a planning failure — it is an asset allocation and risk profile question. A portfolio that returned 12% last year but has a 6.5% withdrawal rate and no longevity plan is not a planning success. Investment performance measured in isolation tells you almost nothing about whether the plan is on track. The planning ratios do.
The following ratios are the types of measures a planning dashboard tracks. Your own model will calculate these from your actual figures — the descriptions here explain what each one means and why it matters.
The cash flow model is the hub. Every variable that affects the plan is a spoke. The planning conversation is the process of deciding which spokes to examine — and in what order.
A cash flow model is not a fixed document. It is a living framework with a central projection — the hub — and a set of variables that can be adjusted to explore different futures. Which variables matter most differs for every plan. The hub-and-spoke structure makes that exploration visible and systematic.
The hub is the baseline model: the central projection built on agreed assumptions, showing what the plan looks like if things go broadly as expected. It is the reference point against which every variable is tested. On its own it is informative. As the centre of a hub-and-spoke framework, it becomes a genuine planning tool.
The hub does not change. What changes is the spoke being examined — one variable at a time, so the effect of each is clear and attributable. Changing multiple variables simultaneously produces a result that is difficult to interpret. Changing one at a time produces insight.
Each spoke represents a variable that can be adjusted in the model to explore a different future. The list below describes what each spoke tests and why it matters — not as a prediction of what will happen, but as a structured way of understanding what the plan can and cannot absorb.
Not every spoke is equally important for every plan. The variables that most affect plan sustainability differ depending on the income structure, the withdrawal rate, the time horizon, and the degree of flexibility available. Part of the planning process is identifying which spokes carry the most weight for your individual situation — and focusing attention there.
Where income is predominantly from portfolio drawdown with little guaranteed income, the growth assumption, sequence of returns, and spending flexibility spokes carry the most weight. Small changes in these variables have large effects on sustainability.
The conversation focuses on: is the withdrawal rate sustainable? What happens if markets underperform in the early years? How much spending flexibility exists?
Where significant guaranteed income covers most income needs, the inflation assumption and longevity horizon spokes tend to dominate. The portfolio is a top-up rather than the primary source.
The conversation focuses on: is the guaranteed income keeping pace with inflation? Is the plan robust to a very long life?
When planning to retire before state pension age, the retirement timing spoke is critical — combined with the income level and sequence of returns spokes. The pre-state-pension years are the most expensive and the most exposed to sequence risk.
The conversation focuses on: what does retiring earlier cost the plan? What is the minimum income needed to make it work?
The traditional financial review asks: how has the investment performed? The hub-and-spoke model asks something more useful: has anything changed that affects which spokes matter, and what does the plan look like now that we test them?
A year in which markets fell but the plan remains robust against the key spokes is not a planning failure — it is a plan working as designed. A year in which markets rose but the withdrawal rate has crept upward and the inflation assumption is looking optimistic is a year that deserves a serious planning conversation regardless of investment performance. The hub-and-spoke framework is what makes the difference between a review that measures market performance and one that measures plan health.
The spokes above address assumption changes — what happens when the numbers in the model shift. There is a second, equally important category: circumstance changes — events in your life that alter the actual inputs to the model, not just the parameters around them.
These are fundamentally different in nature. An assumption change flows through an existing model. A circumstance change may require the model to be re-built from a new reality — because the facts themselves have changed. A plan built on one set of circumstances cannot simply be updated with a new growth rate when those circumstances no longer exist.
The following register describes the life events that most commonly require a model rebuild — and identifies which inputs typically change when each event occurs. It is not a checklist of risks. It is a recognition that a well-maintained cash flow plan accommodates the normal complexity of a life.
Each event is presented with the inputs it typically affects and the reason a planning conversation is warranted. The conversation determines what the new inputs should be. This register explains why that conversation matters.
An assumption change typically affects one variable: inflation rises, growth falls. A circumstance change often affects several inputs simultaneously — and those changes interact. A redundancy at 58 changes income, retirement timing, pension contribution capacity, and possibly the risk profile all at once. The combined effect is not the sum of four separate spoke adjustments — it is a new planning reality that requires a fresh model.
Assumption changes can be modelled in advance and planned for. Circumstance changes arrive at a specific moment — and decisions made in the weeks immediately following can be difficult or impossible to reverse. A pension decision made in the weeks after a bereavement without a re-anchored cash flow model can lock in an outcome that a more considered process would have avoided. The timing of the planning conversation matters as much as its content.
Tax wrappers, investment construction, withdrawal rates, longevity, inflation, income phasing — no single tool can hold all of these simultaneously. The cash flow model can.
The three previous guides in this series each addressed a different dimension of financial planning. The cash flow model is where all three dimensions converge. It is the only tool that can hold tax efficiency, investment construction, and retirement sustainability simultaneously — and show what happens when any one of them changes.
Every one of the following statements can be simultaneously true at the same time — which is why reducing financial planning to any single measure is always insufficient:
A financial plan reviewed against the wrong metrics at the wrong time for the wrong reasons is not a review — it is a performance report. This chapter explains what a meaningful review looks like.
Annual reviews built around investment performance create a predictable and unhelpful pattern: if markets are up, the meeting is comfortable; if markets are down, it is anxious. Neither is a useful proxy for whether the plan is working. The planning ratio framework replaces this with a set of meaningful conditions that actually indicate whether the plan needs attention.
Rather than a calendar-driven review process, the following triggers indicate when a planning conversation is genuinely warranted. Any one of these should prompt a review regardless of when the last one took place — and their absence in any year means the plan is on track and a light-touch review may be sufficient.
This guide has introduced the cash flow model as an educational framework. The next step is to build your own model using your actual numbers. That process begins with a structured data-gathering questionnaire, which collects the information needed to set the model’s parameters.
This series of guides is produced by Iain Ford, Director, FEP&G Ltd for educational purposes only. Nothing in these guides constitutes financial advice, a personal recommendation, or a regulated activity. The illustrative figures, planning ratios, scenario outputs, and projections shown are used for conceptual illustration only. They do not represent predictions of future performance or outcomes for any individual. Investment values can fall as well as rise. You may get back less than you invest. Past performance is not a reliable indicator of future results. The planning ratios and review trigger framework are illustrative tools — appropriate thresholds for any individual will depend on their specific circumstances and should be agreed with a qualified adviser. Always seek advice from a qualified, FCA-regulated financial adviser before making financial planning decisions. © Iain Ford, FEP&G Ltd 2026.