What is DCF? The Logic of Future Value

Let’s talk about the "time machine" of valuation. If you’ve looked at a company’s past performance and its current cash flow, you have the history and the present. But to know if a stock is a bargain today, you have to predict its future.

That is where Discounted Cash Flow (DCF) comes in.

It sounds like intimidating math, but the concept is surprisingly logical. At its core, DCF asks a very simple question: "If I knew exactly how much cash this company would generate for me over the next 20 years, how much would that money be worth to me today?"

The Time Value of Money

The foundation is one idea: a pound today is worth more than a pound in a year's time.

Given £100 today, you can invest it, spend it, or pay down a debt. Given £100 in a year, you can do none of those things for twelve months. You have lost a year of use — and if inflation runs at 3%, the £100 buys about 3% less when it finally arrives. You have also carried the risk that it never arrives at all.

Discounting is just a fancy way of saying: "Let's shrink that future money down to match the size of today's money."

The Three Steps of the DCF Machine

DCF isn't just one big equation; it's a three-step process. It’s like building a ladder.

1. The Forecast (Projecting the Future)

You estimate how much free cash flow the business will generate each year.

Free cash flow is the cash left after everything necessary has been paid — operating costs, tax, and the capital expenditure required to keep the business running. In practice:

Free cash flow = Operating cash flow − Capital expenditure

It is what remains once the bills are settled, which is exactly why it represents money genuinely available to the owners. (This is covered in full in Where the cash actually goes.)

• The Year 1-5 Forecast: You guess how much money they will make. Maybe revenue will grow 10%.
• The Year 6-10 Forecast: You guess what happens then. Maybe growth slows down because they run out of new customers.
• The Logic: If the company is a cash machine that keeps printing money, the numbers on this step will be huge. If the business is struggling, the numbers will be low.

2. The Discount Rate (The Price of Waiting and Risking)

Future cash is worth less than cash today, and the discount rate is how much less, per year.

• High risk → high discount rate → lower present value.
• Low risk → low discount rate → higher present value.

The logic: if you are confident of receiving £100 in five years, you would pay close to £100 today less a modest return for waiting. If you doubt it will arrive, you would pay considerably less.

3. The Terminal Value (The Cliffhanger)

Nobody can forecast a company fifty years out, but companies don't stop after ten. So the model splits the future in two: an explicit forecast for the years you can reason about, and a single terminal value covering everything after that.

• The method: assume the business settles into steady, modest growth forever from the end of your forecast period, and value that perpetuity in one calculation.
• The critical step: that terminal value sits at the end of the forecast period, so it must be discounted back to today exactly like every other future amount. Skipping this is the most common error in beginner DCF models, and it inflates the answer enormously.
• Why it matters so much: terminal value routinely accounts for 60–80% of a DCF's total. The majority of your valuation therefore rests on the part you have the least visibility over.

A worked example. A company will generate £10m of free cash flow one year from now. You require a 15% annual return to take that risk.

Present value = £10m ÷ 1.15 = £8.7m

Two years out, the same £10m is worth £10m ÷ 1.15² = £7.6m. Ten years out, £2.5m. Notice how quickly distant cash loses value at a high discount rate — this is why the choice of rate matters so much, and why high-growth companies whose profits sit far in the future are so sensitive to interest rates.

DCF vs. Market Price: The Value Compass

Once you have a DCF figure — call it your estimate of intrinsic value — you compare it to the market price.

• Market price below your estimate: your assumptions imply the shares are worth more than they cost. This is a reason to look harder, not to act.
• Market price above your estimate: your assumptions imply you would be paying more than the business is worth to you.

The important qualification, and it is not a small one. Your DCF is only as good as your inputs, and a modest change in them moves the answer substantially. If your estimate is 480p and the price is 470p, you have learned essentially nothing — that gap is well inside your own margin of error.

What you are looking for is a gap wide enough to survive being wrong. That is the margin of safety, and the final lesson in this track covers it properly. A DCF does not tell you what to do. It tells you what you would have to believe.

When to Use DCF (And When to Ignore It)

DCF is a powerful tool, but it has a temper. It works best for companies with predictable cash flows.

• Good candidates: regulated utilities, established consumer brands, infrastructure, mature industrials. Businesses whose next five years will probably resemble the last five.
• Poor candidates: early-stage companies with no cash flow to project, cyclical businesses where the answer depends heavily on which year you start from, and banks, whose economics make conventional free cash flow close to meaningless — they are normally valued on price-to-book and return on equity instead.
• Not candidates at all: assets with no cash flows. Gold and cryptocurrencies cannot be valued by DCF in any form, because there is nothing to discount. Their price depends entirely on what the next buyer will pay.

The "Why" Behind the Discount Rate

You might wonder, "How do I know what the right discount rate is?"

The discount rate represents your opportunity cost and risk tolerance.

• Lower risk: a regulated water utility with contracted revenues might justify something in the 6–8% range.
• Higher risk: a small, indebted company in a competitive market might justify 15% or more. You are stating that you require a much larger annual return to accept that uncertainty.

How to Read a DCF Model

If you have access to a financial model, don't just look at the "Result" (the final number). Look at the inputs:

1. Are the Growth Rates Too High? If you are assuming the company will grow at 50% forever, the DCF will be massive. That's unrealistic. Growth slows down eventually.
2. Is the discount rate too low? A 3% rate implies near-certainty. For UK equities a range of roughly 8–12% is common, anchored on the 10-year gilt yield plus an equity risk premium. Check what the model actually used — a low rate is the easiest way to manufacture a high valuation.
3. Is the terminal growth rate reasonable? It must be below the long-run growth rate of the economy — realistically 2–3%. Anything higher implies the company eventually becomes larger than the economy containing it, which is arithmetically impossible. And note that the terminal growth rate must always be below the discount rate, or the formula produces a negative or infinite value.

Summary: The Logic of Future Value

DCF is about translating "promises of the future" into "reality of the present."

• Predict: How much cash will they make? (The Forecast)
• Discount: How risky is it? (The Discount Rate)
• Calculate: How much is that worth today? (The Intrinsic Value)

If the calculated Intrinsic Value is significantly higher than the Market Price, you have found a margin of safety. It means you are buying the future cash flow of a business for a price that gives you a cushion if things don't go exactly as planned.

Remember, this is an estimate. It is the best guess you can make using logic and data, but it is not a crystal ball. Use it as a compass, but never forget that the compass points the way; it doesn't drive the ship.

Disclaimer: This lesson is for educational purposes only and does not constitute financial advice. Discounted Cash Flow models require significant assumptions and are subject to uncertainty. Always do your own research before making investment decisions.