DCF Sensitivity Analysis

A DCF model produces a single number—but that number rests on guesses. Sensitivity analysis shows how much that output shifts if your assumptions change. It’s the honest accounting of how much your valuation depends on hope versus fundamental math.

Why sensitivity analysis matters

Every DCF is built on assumptions: the discount rate, terminal growth, reinvestment rates, far-future profit margins. Change any one of them, and the output changes. Often by billions of dollars.

A naive analyst might build a single “base case” and declare it the value. A thoughtful analyst builds a base case, then asks: What if I’m wrong? If I’m wrong by 0.5%, does that destroy the investment thesis? Or does the thesis hold even across a wide range of plausible outcomes?

Sensitivity analysis answers that question. It’s also a tool for spotting fragile assumptions: if a 1% change in WACC swings your valuation by 30%, you’re overly dependent on nailing that single input, and your margin of safety is thin.

The two-way table: WACC and terminal growth

The classic sensitivity output is a two-dimensional table. One axis is WACC (say, 6% to 11%); the other is terminal growth rate (say, 1% to 4%). Each cell shows the resulting equity value.

Here’s a stylized example for a $5B revenue firm:

This table tells a story. At 8% WACC and 3% growth, value is $48B. But if you’re wrong and WACC is actually 7%, value jumps to $57B. If growth is 4% instead, it’s $56B. If both assumptions are off in your favor, you get $66B.

But here’s the kicker: if WACC is 10% (higher risk than you thought), or if long-term growth is only 1%, the valuation collapses to $31B. The range is $31B to $79B for the same company. Which assumption gets right determines whether you buy, hold, or sell.

Why these two inputs?

WACC and terminal growth are the heavyweights of DCF because they drive the terminal value—often 60–80% of total value. In a standard DCF, terminal value is:

TV = Year 5 FCF × (1 + g) / (WACC − g)

Notice the denominator: WACC minus growth. As growth creeps toward WACC, the denominator shrinks and the fraction explodes. A 3% growth at 8% WACC gives a denominator of 5%. A 3.5% growth at 8% WACC gives 4.5%. That 0.5% shift widens the terminal value multiple by 11%.

Similarly, a 0.5% shift in WACC from 8.0% to 7.5% widens the denominator from 5% to 4.5%, also an 11% increase in value. The sensitivity is symmetric in WACC and growth—a dangerous symmetry, because WACC is often more controllable (you can research competitor costs and debt spreads) while growth is speculative.

Building a sensitivity table

The mechanics are simple:

1. Define your base-case assumptions: WACC = 8%, terminal growth = 3%, forecast free cash flow = $2B in year 5.
2. Choose a range: WACC from 6% to 10% (±2%), growth from 1% to 5% (±2%).
3. For each WACC–growth pair, plug into the DCF formula and calculate resulting equity value.
4. Plot the results in a table, highlighting your base case.

Most software (Excel, financial modeling platforms) makes this a one-line lookup or data-table function. The art is choosing the ranges. Too narrow, and you’re not stress-testing. Too wide, and you include implausible scenarios (a 5% perpetual growth rate for most mature companies is fantasy; a 6% WACC assumes no equity risk premium).

One-way sensitivity: isolating single inputs

A one-way sensitivity holds everything constant except one variable and plots the result as a line graph.

For instance, hold WACC at 8% and growth at 3%, then vary the profit margin assumption from 4% to 8%. You’ll see a line sloping upward: higher margins mean higher cash flows and higher value. If the line is steep, margin assumptions matter a lot. If it’s flat, you’re less exposed to that input.

One-way sensitivity is useful for identifying your true risks. Many analysts assume cost inflation, tax changes, or capital expenditure surprises are decisive, only to run a sensitivity and discover that 99% of the value swing comes from terminal growth assumptions, not operation detail.

Multi-factor sensitivity: scenarios

A richer approach is scenario analysis: define a “base case,” a “bull case,” and a “bear case,” each internally consistent.

• Base case: 8% WACC, 3% terminal growth, 5% margin. Value = $48B.
• Bull case: 7% WACC (lower risk perceived), 4% growth (competitive strength holds), 6% margin (scale advantages). Value = $66B.
• Bear case: 9% WACC (higher risk), 2% growth (commoditizing market), 4% margin (price pressure). Value = $38B.

This three-point range ($38B to $66B) reflects a realistic band of outcomes tied to strategic narratives, not just mathematical extremes.

Using sensitivity to set a price target

A disciplined investor combines sensitivity analysis with a margin of safety.

Suppose sensitivity shows a range of $35B to $65B. You’re not equally confident in all outcomes. You might assign:

• 50% probability to base case = $48B.
• 25% probability to bull case = $66B.
• 25% probability to bear case = $38B.

Probability-weighted value = 0.5×$48B + 0.25×$66B + 0.25×$38B = $51B.

If the stock is trading at $40B, it’s cheap. If it’s at $55B, it’s fair. If it’s at $65B, it’s expensive—the market is pricing in the bull case with high confidence, leaving no margin for error.

Pitfalls: garbage in, garbage out

Sensitivity analysis doesn’t cure bad assumptions—it exposes them.

If your base case WACC is 5% (unrealistically low cost of equity), a sensitivity table will show absurdly high valuations even in the “bear case.” Garbage assumptions produce garbage ranges. Before running sensitivity, sanity-check your inputs against peers, historical data, and risk-free rates.

Also, sensitivity analysis can encourage false precision. A table suggesting value is “between $40B and $60B” might imply confidence you don’t have. The true answer is: I don’t know. This range shows what factors matter most, and how wide the uncertainty is.

Finally, don’t assume the axes are independent. If interest rates rise, WACC rises and growth often falls (corporations cut capex). Sensitivity tables treat them separately, which understates tail risk in a rising-rate environment.

Communicating sensitivity results

A clean sensitivity table beats pages of prose. One table and one sentence—“Base case value is $48B; plausible range is $38B–$66B; key driver is terminal growth assumption”—conveys more than paragraphs of caveats.

For presentations, highlight the base case cell. Color-code the table: green for upside, red for downside, yellow for the central band. Let the visual reveal which regions are most likely and which are outliers.

And always state your assumptions clearly: “Assumes WACC of 8%, calibrated to current Treasury rates plus 3.5% equity risk premium; terminal growth of 3%, consistent with long-run GDP growth; margin expansion from 5% to 6% over 5 years based on operational initiatives.”

See also