The metric that answers “was it worth it?”
Return on investment (ROI) is a percentage that measures how much you gained or lost relative to how much you spent. It’s used to evaluate marketing campaigns, business decisions, product investments, financial assets, and almost any situation where you spend money expecting a return.
The formula looks simple, and it is — but the results are only as useful as the inputs. Understanding what goes in and what doesn’t is the difference between a meaningful ROI figure and a misleading one.
Calculate ROI instantly with ROI Calculator.
The ROI formula
ROI = (Net Profit / Cost of Investment) × 100Where:
- Net Profit = Revenue generated minus the cost of investment
- Cost of Investment = Everything you spent to generate that revenue
Example: You spend £5,000 on a marketing campaign and it generates £8,000 in revenue.
- Net Profit = £8,000 − £5,000 = £3,000
- ROI = (£3,000 / £5,000) × 100 = 60%
A positive ROI means you made more than you spent. Negative ROI means you lost money. Zero ROI means you broke even.
What to include in “cost of investment”
This is where ROI calculations most often go wrong. People include the obvious direct costs but miss the less visible ones, producing an inflated ROI figure that doesn’t reflect reality.
Include:
- Direct spend (ad budget, software licenses, agency fees)
- Staff time (at an hourly rate — even internal staff has a cost)
- Tool and platform costs specific to the project
- Any overhead directly attributable to the investment
- Opportunity cost if relevant (what else could that money have done?)
Common omissions:
- Internal staff hours spent planning, executing, and reviewing
- Partial costs of shared tools or infrastructure
- Time spent on revisions or fixes
If you run a £2,000 ad campaign but your marketing manager spent 20 hours managing it (at £50/hour), the real cost is £3,000, not £2,000. The ROI changes significantly.
Interpreting the result
A positive ROI doesn’t automatically mean an investment was worthwhile. Context matters:
Time period — A 10% ROI over one month is excellent. A 10% ROI over five years is poor. ROI doesn’t account for time unless you calculate annualised ROI.
Risk — A 15% ROI from a safe, predictable source may be more valuable than a 25% ROI from something unreliable.
Comparison — ROI is most useful when comparing alternatives. A 40% ROI on campaign A vs. 80% on campaign B with the same budget tells you where to invest next.
Threshold — Many businesses set a minimum acceptable ROI (hurdle rate). An investment might have positive ROI but still be rejected because it doesn’t exceed the threshold needed to justify the risk and effort.
Marketing ROI specifically
Marketing ROI has an additional complication: attribution. When a customer converts, which touchpoint gets credit? The first ad they saw, the last email they clicked, or all interactions equally?
Last-touch attribution — 100% credit to the final interaction before conversion. Simple but ignores everything that built awareness and consideration.
First-touch attribution — 100% credit to the first interaction. Overvalues awareness channels.
Linear attribution — Equal credit to every touchpoint. More accurate but harder to act on.
Time-decay attribution — More credit to touchpoints closer to conversion. A reasonable middle ground.
For most purposes, last-touch or linear attribution gives a workable approximation. The important thing is to use the same model consistently when comparing campaigns.
When to use other metrics alongside ROI
ROI is excellent for comparing investments of the same type, but it doesn’t capture everything. For business decisions, consider pairing it with:
Payback period — How long until the investment pays for itself. A 200% ROI achieved over 5 years may be less attractive than a 100% ROI achieved in 6 months.
NPV (Net Present Value) — Accounts for the time value of money. More accurate for long-term investments but requires estimating a discount rate.
Customer Lifetime Value (CLV) — For customer acquisition, the ROI of acquiring one customer depends on how much they spend over their lifetime, not just their first purchase.
Use ROI Calculator for quick calculations, and Growth Rate Calculator to measure how your returns are changing over time.