Returns and value: NPV, ROI, EBITDA, and payback

Intuition

When a company decides whether to build a factory, buy a rival, or launch a product, it's really asking one question: will the money we get back be worth more than the money we put in? The complication is timing, cash arrives over years, and a dollar next decade is worth less than a dollar now. The vocabulary of returns (NPV, ROI, payback, EBITDA) exists to make that comparison fair.

Think of it like lending money to a friend. You don't just want it back, you want enough extra to make the wait, and the risk, worthwhile. That "extra" is the return.

Framework

• Time value of money: future cash is worth less than present cash; we discount it back to today.
• NPV (Net Present Value): sum of all future cash flows discounted to today, minus the upfront cost. Positive NPV = value-creating; do it.
• ROI / ROIC: return as a percentage of money invested. ROIC checks whether returns beat the cost of capital.
• Payback period: how long to recover the initial outlay. Fast, intuitive, but ignores discounting.
• EBITDA: earnings before interest, tax, depreciation, amortization, a proxy for operating cash flow, used for comparison and valuation multiples.

Worked Example

A retailer weighs a $2M store renovation expected to add $600K of profit a year for five years. Simple payback = $2M / $600K ≈ 3.3 years, fine for a five-year horizon. On NPV, you'd discount each year's $600K back to today; even at a 10% discount rate the five years of cash sum to well above $2M, so NPV is positive, go ahead. If instead the benefit were only $300K/year, payback stretches past six years and the NPV likely turns negative, kill it.

Now watch payback lie. Project A: $1M cost, $500K/year for exactly two years, payback in 2 years, but total cash is just $1M, so NPV is negative at any discount rate. Project B: $1M cost, $250K/year for ten years, payback takes 4 years, yet $2.5M of total cash means NPV at 10% is strongly positive (the discounted flows sum to roughly $1.5M). Payback crowns A; NPV correctly crowns B. That's why payback is a screen, never the decision.

In the room

Name the lens before the math: "I'll check payback first for speed, then NPV for whether it actually creates value." Narrate payback as one clean division: "$2 million over $600K a year, 20 over 6, call it 3.3 years." For NPV you almost never compute precisely live; reason about it out loud instead: "Five years of $600K is $3M undiscounted, even with a 10% haircut each year, that comfortably clears the $2M cost, so NPV is positive." Directional discounting, spoken confidently, beats fumbling exponents at the whiteboard. And if EBITDA comes up, fence it in one line: "EBITDA tells us about operations, it isn't cash the owners keep." The interviewer is scoring whether time-value thinking is instinctive: do you reach for the discount intuition unprompted, or treat all dollars from all years as equal?

Pitfalls

• Comparing cash flows from different years without discounting them.
• Treating EBITDA as "profit", it ignores real costs like interest, tax, and the capital that wears out.
• Choosing a project on payback alone, ignoring whether the later cash is large enough to justify it.