How is email marketing ROI calculated?

The basic formula is: (Revenue from email - Cost of email program) / Cost of email program × 100. The result is a percentage. If you spent 500 euros and attributed 10,000 euros in revenue, your ROI is (10,000 - 500) / 500 × 100 = 1,900%.

Let's make the inputs concrete:

Revenue from email = the sum of all conversions tracked back to email clicks within your attribution window. Most ESPs report this if you have conversion tracking set up. Some teams also add revenue from auto-responder sequences, welcome flows, and cart abandonment emails, not just one-off campaigns.

Cost of email program = everything it takes to run email: ESP fees, design costs, copywriting (yours or contracted), testing tools, list management overhead. Many calculations forget the loaded cost of internal time. If you spend 8 hours a week on email at a fully-loaded hourly rate of 100 euros, that's 3,200 euros per month in internal cost alone before any software fees.

Common mistakes that inflate ROI: (1) using last-click attribution that double-counts revenue from subscribers who also saw your ads, (2) excluding list-building costs from the cost side, (3) using a too-long attribution window (90 days) that credits email for purchases that were going to happen anyway.

Common mistakes that deflate ROI: (1) using a too-short attribution window that misses delayed decisions, (2) only counting completed purchases and ignoring lead-stage conversions, (3) not measuring at all and assuming email doesn't convert.

If your calculation looks unusual (either too good or too low), check your attribution window first. It's usually the culprit. Our SOS hotline is free if you're not sure how to set this up for your specific setup. Conversion tracking needs to be solid before ROI calculations mean anything.