How a discounted cash flow model works

The one idea underneath all of it

A business is worth the cash it will hand its owners in the future. A pound arriving in ten years is worth less than a pound today, because today’s pound can be invested in the meantime and because the future one might never arrive. A discounted cash flow model is simply that sentence turned into arithmetic: estimate the future cash, then shrink each future amount according to how far away and how uncertain it is.

Everything else is bookkeeping. The formulas look intimidating, but there are only four moves: project the cash, discount it, estimate what happens after the projection stops, and work out how much of the result belongs to shareholders rather than lenders.

Step one: project the cash flow

The starting figure is free cash flow: the cash a business generates from operations after paying for the equipment and infrastructure it needs to keep running. The usual approximation is cash from operations minus capital expenditure, both of which sit on the cash flow statement.

Use the UNLEVERED figure, which is measured before interest payments. This matters more than it sounds, and it is the source of the most common mistake in homemade models. Unlevered cash flow belongs to everyone who financed the business — lenders and shareholders together. We deal with that in step four.

Then grow it. Our tool offers three patterns. A single rate applies the same growth to every year, which is fine for a stable business. Two stages model a company growing quickly now and settling later. Per-year lets you type each year individually, which is the honest choice when you actually have a view on specific years.

Growth compounds from the previous projected year, not from the starting figure. Ten percent growth for three years takes 100 to 110, then 121, then 133.1 — not to 130.

Step two: discount it back

Each projected year is divided by (1 + r) raised to the power of the year number, where r is your discount rate. Year one is divided once, year two twice, and so on. Money further away is divided more, which is exactly the intuition we started with.

The discount rate is doing two jobs at once: it represents the return you require, and it represents risk. A riskier business deserves a higher rate, which mechanically produces a lower value. There is no objective correct rate. The weighted average cost of capital is the standard estimate, and the tool includes a calculator for it, but it is still an estimate built on further estimates.

By default the tool uses the end-of-year convention, which assumes each year’s cash lands on the final day. The mid-year option assumes it arrives evenly through the year, so it discounts by half a year less and produces a slightly higher value. Neither is more correct; what matters is applying the same convention to the forecast and the terminal value, which the tool does automatically.

Step three: the terminal value, where most of the answer hides

Businesses do not stop after your forecast window. The terminal value captures everything beyond it, and it routinely accounts for well over half the total. That is worth sitting with: most of a typical DCF’s answer comes from the part you did not forecast in detail.

The perpetuity growth method assumes cash flow grows at a constant modest rate forever. The formula takes the final forecast year, steps it up by one more year of growth, and divides by the discount rate minus the growth rate. The step-up matters because the perpetuity starts the year after the forecast ends.

That subtraction is also the method’s weak point. As the growth rate approaches the discount rate, the denominator approaches zero and the value explodes towards infinity. If growth equals or exceeds the discount rate, the formula is meaningless — it describes a company outgrowing the entire economy forever. Our tool refuses to compute this case and tells you why, rather than displaying an enormous or negative number.

The exit multiple method is the cross-check. Instead of assuming perpetual growth, it assumes the business is sold at some multiple of its final-year cash flow. Because it ignores the growth rate entirely, it fails differently, which is precisely what makes it a useful second opinion. If the two methods disagree wildly, your terminal assumptions are doing too much work.

Step four: from the whole business to one share

Adding the discounted forecast to the discounted terminal value gives the enterprise value — the value of the entire operating business, funded by lenders and shareholders together.

Shareholders do not own that. Lenders are paid first. To get the equity value you subtract debt and add back cash, because cash is already owned outright. The result divided by the diluted share count is the value per share.

Skipping this step is the single most common error in an amateur DCF, and it is not a small one. A company with 300 million of net debt and 50 million shares is overvalued by exactly six pounds a share if you forget it. Our tool shows this bridge as an explicit four-line chain so you can check it.

One sign convention catches people out: if a company holds more cash than debt, net debt is negative, and subtracting a negative adds. A net-cash business is worth MORE than its enterprise value per share, not less.

Why the answer moves so much

Small changes in the discount rate and terminal growth rate produce large changes in the output, because both feed a denominator that can approach zero. This is not a flaw in the implementation; it is the nature of dividing by a small difference between two uncertain numbers.

This is why the tool shows a sensitivity grid rather than a single figure. Reading it honestly means accepting that a DCF produces a range, and that the width of that range is itself information. If the plausible range spans a factor of three, the model is telling you it cannot answer the question precisely — and that is a legitimate finding, not a failure.

Treat the output as a way to make your own assumptions explicit and testable, not as a measurement. The model cannot know more than you told it.

Questions

Limitations

• A DCF is only as good as its assumptions, and every assumption here is yours. The tool performs arithmetic; it has no view on whether your inputs are reasonable.
• The perpetuity growth method is extremely sensitive to the gap between the discount rate and the terminal growth rate. Small input changes produce large output changes.
• The model assumes a stable capital structure and a constant discount rate for the whole period. Real companies refinance, change risk profile, and issue shares.
• It cannot value a business with negative free cash flow, which rules out many early-stage companies. A DCF is the wrong instrument for those.
• Cyclical businesses, banks and insurers need different treatment. A single trailing cash-flow figure can badly misrepresent a company at the top or bottom of its cycle.