Definition (canonical)
ROI (Return on Investment) measures how much an investment returned relative to what it cost: `ROI = (gain − cost) ÷ cost × 100%`. Spend 10,000 on a campaign that produces 14,000 of margin → ROI = 40%. It is business's universal comparator — and the most manipulated number in every pitch deck.
Computing it honestly — both sides of the fraction
The fraud usually hides in definitions, not arithmetic. The gain: use MARGIN, not revenue — a campaign "returning" 14,000 of revenue at 30% gross margin actually returned 4,200 against 10,000 of spend: ROI −58%, not +40%; revenue-based ROI flatters by exactly your cost structure. The cost: fully loaded — the agency fee AND the internal hours, tools, and management attention; a "free" organic channel eating half a marketer's year is not free. Attribution: the gain must be INCREMENTAL — sales that would have happened anyway don't count (holdout tests and geo-splits exist precisely to separate lift from noise). The honest template: incremental margin, full costs, stated time window.
Time — the dimension ROI ignores
Raw ROI has no clock: 20% over three months and 20% over three years are different universes wearing the same number. For comparability, annualize: `(1+ROI)^(365/days) − 1` — the 3-month 20% becomes ~107% annualized, the 3-year one ~6%. This is where ROI hands over to its siblings: CAGR for multi-year returns, payback period when the question is "how fast is cash back", NPV/IRR when money's time value and multiple cash flows matter (large capex deserves the full toolkit, not a single ratio). Rule of practice: any ROI quoted without a period is marketing, not measurement.
Using ROI to decide — thresholds and traps
Decision logic: compare against your opportunity cost — the return of the next-best use of money (parking cash, paying down debt, the other project); an ROI of 15% loses to a 20% alternative and wins against 5% — there is no universal "good ROI". Portfolio reading: rank projects by annualized ROI on incremental margin, fund from the top until capital or capacity runs out — but keep two guards: risk-adjustment (a certain 15% can beat a coin-flip 40%) and strategic blindness (brand, infrastructure and compliance investments show terrible short-window ROI and are still mandatory; measure them on longer windows rather than exempting them from math entirely). And when someone shows you 900% ROI — ask for the three definitions: gain, cost, window.
FAQ
ROI vs ROAS? ROAS = revenue ÷ ad spend (a media-buying dial); ROI = margin-based and full-cost (a business decision dial) — a ROAS of 4 can be an ROI below zero on thin margins.
Can ROI be computed before investing? As projected ROI — fine, if labeled and stress-tested; the sin is presenting projections with realized-number confidence.
What about hard-to-quantify returns? Estimate ranges rather than surrendering: retention lift, hours saved × loaded rate, risk reduction — imperfect numbers beat adjectives.
Related: Margin · CAGR · CAC Payback · Break-Even Reviewed: 2026-07-16 · Sources: corporate finance canon