How to Calculate Your Actual Email Marketing ROI

Your ESP says email generated $200K last month. Your CFO says total revenue was $500K. Is email responsible for 40% of revenue? Probably not.

The attribution problem

Most ESPs use a generous attribution window: 5-day click, 1-day open (sometimes 5-day open). This means if someone opens your email on Monday and buys on Friday through a Google ad, email gets the credit.

With Apple MPP marking most emails as "opened," the 1-day open window captures purchases from people who never saw your email. Your ESP is counting revenue from Apple bots.

How to fix it

Step one: Switch to click-only attribution. Remove the open window entirely. If someone clicked a link in your email and purchased within 5 days, that is email revenue. If they did not click, email did not drive that purchase.

Step two: Compare your ESP revenue against your platform (Shopify, Stripe). If your ESP says email did $200K but your total revenue is $500K and you also have $180K attributed to paid ads and $120K to organic, the math does not add up. Multiple channels are claiming the same purchases.

Step three: Use a simple last-click model as your baseline. The last channel a customer interacted with before purchasing gets the credit. This undervalues email (which often assists earlier in the journey), but it gives you a conservative floor.

The realistic number

In our experience, switching from open+click attribution to click-only reduces reported email revenue by 30-50%. That sounds bad, but the remaining number is real. You are making decisions based on actual performance.

For our e-commerce clients, email typically drives 15-25% of total revenue on a click-only model. For our best-performing accounts, it reaches 30-35%.

Why this matters for your budget

If you are allocating budget based on inflated email revenue, you are underinvesting in channels that are actually driving those purchases. Get the attribution right, and you make better decisions across every channel, email included.

Monthly reporting framework

We report four numbers to clients every month: Email revenue (click-only attribution). Revenue per recipient (by flow). List growth (net of unsubscribes). Deliverability (inbox placement %). Everything else is detail. These four numbers tell you if the program is healthy.