Email marketing ROI is the return generated by your email programme divided by what it cost to run, expressed as a ratio or a percentage. The formula is not the hard part. Deciding what counts as revenue and what counts as cost is the hard part, and it is where most published ROI figures fall apart.
The formula, and the two arguments inside it
ROI = (attributable revenue − programme cost) ÷ programme cost
Argument one: which revenue is attributable? If a customer receives your newsletter on Tuesday and buys on Thursday after a Google search, is that email revenue? Under last-click, no. Under a 7-day view-through window, yes. The two answers can differ by several times, and neither is wrong — they are answering different questions. Pick one, write it down, and never change it mid-comparison. Email attribution covers the options.
Argument two: what counts as cost? This is where the famous benchmark quietly cheats.
Why the $36 per $1 figure is not your number
The widely cited claim that email returns roughly $36 for every $1 spent comes from marketer surveys, and it has two properties worth understanding before you repeat it.
First, the denominator is usually just the platform subscription. Not the salary of the person writing the emails, not the designer's time, not the cost of the discount codes. If you count a $50 monthly subscription as the entire cost of a programme that occupies a person three days a week, of course the ratio is spectacular.
Second, the numerator is usually last-click attributed revenue with no incrementality test. Some of the customers who clicked an email and bought would have bought anyway. Email is unusually prone to this because it reaches people who are already customers — the population most likely to purchase without prompting.
None of which means email is a bad channel. It is a very good channel, and it is almost certainly your cheapest per dollar of revenue. It just is not thirty-six times better than everything else.
Calculating a number you could defend
Costs, all of them:
- Platform subscription, including overage
- Hours spent × loaded hourly cost — writing, design, build, QA, analysis
- Design and template work, amortised
- Deliverability tooling and list verification
- Discounts and incentives given specifically in email
- A share of any CDP or data infrastructure email depends on
Revenue, honestly:
- Attributed revenue within your fixed window, deduplicated across campaigns and flows
- Minus expected returns and refunds at your normal rate
- At gross margin, not at top-line revenue, if you are comparing against channels or making a spend decision
Gross margin is the step that most changes the answer. A campaign that produces $10,000 of revenue at 30% margin contributed $3,000. Comparing a $10,000 revenue figure against a $2,000 cost gives 5:1; comparing the $3,000 contribution gives 0.5:1. Those lead to opposite decisions.
The incrementality question
The honest way to know what email contributed is a holdout: exclude a random 5–10% of the eligible audience from a campaign or a flow, then compare revenue per person between the holdout and the treated group. The difference is incremental; everything else is revenue you would have earned regardless.
Holdouts are uncomfortable because they involve deliberately not emailing people who might buy. They are also the only method that answers the question. Run one on your highest-volume automated flow — the abandoned cart is the usual candidate, and often the most surprising — and keep it running permanently. The cost is a few percent of that flow's revenue; the return is knowing whether the flow works.
Where the returns actually come from
When you break email ROI down by campaign type, the pattern is consistent across businesses:
Automated flows dominate. Abandoned cart, welcome, post-purchase and win-back typically account for a minority of sends and a majority of revenue, because they fire at the moment of intent. They are also built once and run for years, which makes their ongoing cost close to zero and their ROI arithmetic unusually favourable.
Broadcasts carry the relationship. Newsletters and announcements convert at lower rates but keep the list warm, which is what makes the flows work at all. Measuring a newsletter purely on its own attributed revenue undervalues it.
Reactivation is high variance. Sometimes excellent, sometimes negative once you count the deliverability cost of mailing dormant addresses.
If your ROI is disappointing and your flows are not built, build the flows before optimising anything else. For a month-to-month scoreboard that survives list changes, revenue per subscriber is the companion metric to this one. Our ROI calculator will put rough numbers on the upside for your list size.
The cost lever nobody pulls
The denominator is under your control in a way the numerator is not. Contact-based pricing means your platform cost rises with list size whether or not the new contacts ever buy — so a list that doubles doubles the cost while the revenue lags. Pricing that charges for sends rather than for stored contacts keeps the denominator tied to activity. That is why unlimited contacts is a pricing decision rather than a feature, and it is worth checking against your own numbers on the pricing page.
Frequently asked questions
What is a good email marketing ROI?
Any positive figure calculated with full costs and gross margin is a genuinely good result, and most well-run programmes land somewhere between 3:1 and 15:1 on that basis. Ratios above 30:1 almost always come from counting only the software subscription as the cost.
Should I use revenue or gross margin in the calculation?
Gross margin, for any decision about whether to spend more. Top-line revenue overstates contribution by whatever your cost of goods is, and for physical products that is most of it.
How do I prove email caused the revenue?
Run a holdout. Exclude a random slice of the eligible audience, compare revenue per person against the treated group, and the difference is the incremental effect. Nothing else distinguishes revenue email caused from revenue that would have arrived anyway.
Which email type has the highest ROI?
Triggered automated flows, by a wide margin. They are built once, run indefinitely, and fire at the moment someone has shown intent, so both sides of the ratio work in their favour.
