A discounted cash flow model — DCF for short — answers one question: if you owned this whole business, what is the future cash it throws off worth to you today? Everything else in the model is machinery built around that single idea.
It matters because price and value are not the same thing. The market quotes you a price every second. A DCF is one of the few tools that tries to estimate value from the ground up, independent of what the crowd is paying this morning.
The one idea underneath it: a dollar later is worth less than a dollar now
If someone offers you $100 today or $100 in five years, you take it today — you could invest it, and there's risk the future payment never shows up. So future money has to be "discounted" to make it comparable to money in hand.
A DCF does this to a company's future cash flows. Project the cash for each of the next several years, shrink each year's figure back to today's terms, add it all up, and you get an estimate of what the business is worth right now.
The three things you actually have to estimate
Strip away the spreadsheet and a DCF is just three judgement calls:
- The cash flows. Usually free cash flow — the cash left after the company pays its bills and reinvests to keep running. Not accounting profit; actual cash.
- The discount rate. How much to shrink each future year. For a whole-firm DCF this is the WACC (weighted average cost of capital) — blended cost of the company's debt and equity. Riskier business, higher rate, lower value.
- The terminal value. You can't forecast forever, so after the explicit years (often 5–10) you assume the cash grows at a steady, modest rate forever and capture that as one lump sum. This "terminal value" is frequently the majority of the answer — which is exactly why it deserves suspicion.
A deliberately tiny example
Say a company produces $100 of free cash flow next year, growing 5% a year, and you discount at 10%.
| Year | Free cash flow | Worth today (at 10%) |
|---|---|---|
| 1 | $100 | $91 |
| 2 | $105 | $87 |
| 3 | $110 | $83 |
Each year's cash is real, but the further out it sits, the less it's worth to you now. Sum the discounted years, add the terminal value, divide by the share count, and you have an estimated value per share. Compare that to the market price: higher means potentially undervalued, lower means the opposite — if your assumptions hold.
Where DCFs go wrong
The math is trivial. The assumptions are everything, and small changes swing the answer hard:
- Terminal value dominates. If 70% of your valuation comes from a number you assumed about the year 2045, you're not valuing a business — you're valuing a guess about the distant future.
- The discount rate is a lever. Nudge WACC by one percentage point and "fair value" can move 15–20%. It's easy, consciously or not, to back into the number you wanted.
- Garbage growth in, garbage value out. Plug in heroic growth and any company looks cheap.
This is why a DCF is best read as a range, not a single price — and why sensitivity tables (value across different WACC and growth combinations) are more honest than one headline figure.
How to actually use one
Treat a DCF as a structured way to ask "what would have to be true for today's price to make sense?" rather than a verdict. A reverse DCF flips it: instead of outputting a price, it solves for the growth rate the current market price is implying — then you judge whether that growth is plausible. Often more useful than the forward version, because it pins down what you're really betting on.
Pair it with simpler cross-checks — multiples like P/E and EV/EBITDA, what comparable companies trade at — and treat agreement across methods as the signal, not any single model's output.
The short version
A DCF values a company by its future cash, discounted to today. Three inputs drive it: the cash flows, the discount rate, and the terminal value. The arithmetic is easy; the assumptions are where the judgement — and the mistakes — live. Use it to understand what a price implies, not to manufacture a target you already wanted.