Sanity-Checking a Finished DCF

A DCF can pass every formula check — the discounting is correct, the terminal value formula is applied properly, the model ties out to the penny — and still imply that a mid-size regional retailer will be worth more than the entire US economy in forty years. The model isn't broken; the assumptions feeding it are. Checking a DCF's internal arithmetic is necessary but nowhere near sufficient — the numbers it spits out need to be checked against what's actually plausible in the real world.

The checks that catch the most damage

Terminal value as a share of total value. If the terminal value makes up 85–95% of a DCF's total value, nearly the entire valuation rests on assumptions about a period more than a decade out, which should be flagged and stress-tested even if the near-term forecast is well-researched.

Perpetual growth rate versus the economy. A company's cash flows cannot grow faster than the overall economy forever — a terminal growth rate above roughly the long-run nominal GDP growth rate (commonly 2–4% for developed economies) implies the company eventually becomes the entire economy, which is not a plausible steady state.

Implied return on capital in the terminal year. If the terminal-year numbers imply a return on invested capital far above what any company in the industry has sustained historically, the growth and margin assumptions feeding the model deserve a second look.

Cross-check against multiples. If the DCF's implied valuation is wildly out of line with what comparable companies actually trade at, that's not automatically a sign the market is wrong — it's a prompt to check whether the DCF's assumptions (growth, margin, discount rate) are actually defensible, or whether an error has crept in.

Worked example

A DCF for a consumer goods company produces an enterprise value of $8.0 billion, of which the terminal value contributes $7.4 billion.

1. Terminal value share: $7.4/8.0 = 92.5\%$ — a flag that nearly the entire valuation rests on the terminal-year assumptions.
2. Checking the terminal assumptions: the model uses a 4.5% perpetual growth rate, above the roughly 2.5% long-run nominal GDP growth typically used as a ceiling — a second flag.
3. Checking implied ROIC in the terminal year: the model's terminal operating income and invested capital imply a 35% return on invested capital, well above this industry's historical range of 12–16% — a third flag, and now a pattern.
4. Cross-check against peers: comparable consumer goods companies trade at 12x EV/EBITDA; this DCF's $8.0 billion implies roughly 19x the company's current EBITDA — well outside the peer range, consistent with the three flags already raised.

Lowering the terminal growth rate to 2.5% and the implied terminal ROIC to a level consistent with peers brings the DCF down to roughly $5.1 billion — in line with the peer multiple range, and a far more defensible number than the original $8.0 billion.

What this means in practice

Sanity checks are cheapest to run, and most valuable, at the very end of a DCF build, once every number is in place — running them earlier means re-checking after every subsequent change, but skipping them entirely is how obviously wrong valuations survive into a final report. A DCF that fails several of these checks isn't necessarily useless, but every failed check should trace back to a specific assumption that gets revisited and explicitly justified, not silently left as-is.