Discount codes lift conversions — but they can also quietly skew who gets credit for them. Coupon sites and browser extensions often claim the last click right before checkout, even when someone else drove the customer. Here's how to measure discounts fairly.
Where the problem arises
- Last-click theft. The customer searches for a code, clicks a coupon site, it becomes the "last channel" and takes credit for a conversion it didn't drive.
- Browser extensions. Coupon extensions can inject an affiliate click in the background.
- Wrong value. If you send the pre-discount value, revenue is inflated; if post-discount without handling returns, a different problem.
How to measure it fairly
- Send the actual amount paid. I.e. post-discount — that's the real revenue.
- Watch which codes and channels actually drive conversions, not just where the last click landed. Context in conversion attribution.
- Evaluate the contribution of coupon channels critically — how much is new acquisition vs. people who'd have bought anyway (see incrementality).
Where server-side comes in
Server-side tracking gives one place to control the conversion value (post-discount) and the attribution logic before data leaves for the platforms. Reliable, complete measurement is also a prerequisite for knowing which channel drove the customer before they found the code.
Summary
Discount codes and coupon sites can steal attribution and inflate credit. You defend against it by sending the real post-discount value, evaluating coupon channels critically and keeping attribution clean — which server-side tracking lets you control from one place. More in the complete guide.