The flawed metric most marketers look at
A lot of self-proclaimed email experts obsess over sign-up form conversion rates. They run an A/B test on a pop-up, see that one offer collected 1% more email addresses, and declare a winner on the spot.
That is a mistake.
When you optimise your sign-up forms, submission rate is not the metric that matters most. What happens to the revenue after someone gives you their email address is what pays the bills. A form can generate thousands of leads, but if those leads buy once at a tiny order value or never convert at all, the offer has failed.
The real test: 15% off versus $50 off
We ran a split test for an ecommerce client comparing two distinct introductory incentives. One version offered 15% off, while the other offered $50 off.
On paper, $50 sounds like a substantially larger discount, especially to a customer browsing mid-tier items. Plenty of marketers would assume the fixed dollar discount would destroy the percentage offer. In reality, the form submission volume was practically identical, pulling roughly 10,000 submissions per variant.
If you stopped looking at the data right there, you would call the test inconclusive. But the moment you look at the backend Shopify data and Klaviyo attribution, the winner is obvious.
Why percentage discounts drive higher average order value
The code for 15% off dramatically outperformed the $50 off code across gross sales and discounted orders. It almost doubled the total revenue generated from the sign-up flow.
The mechanics behind this come down to buyer psychology. Customers know that with a percentage discount, the more they spend, the more they save. A fixed dollar discount caps the perceived reward immediately, so shoppers only add enough to their cart to qualify for the threshold.
You can see the difference directly in the numbers. The percentage discount generated an average order value of $422, compared to just $383 for the $50 discount. That extra $39 per order adds up quickly when you are processing hundreds of orders a week.
What about your profit margins?
Brand owners often panic about percentage discounts on big carts. They worry that if a customer spends $1,000, a 15% discount means giving away $150 instead of capping the loss at $50.
Here is the thing: you are still walking away with substantially more top-line cash and a higher average order value. If your margins are so fragile that a standard welcome discount wipes out your profit on a high-value order, you have a pricing problem, not a discount problem.
Your acquisition discounts should already be factored into your unit economics. You should easily break even or make a profit on the first transaction. If you cannot afford a 15% introductory offer, you need to revisit your margins rather than throttling customer spend with restrictive vouchers.
Stop running tests on solved problems
Agencies love convincing brand owners to run endless tests on things that have already been proven across thousands of stores. Testing fixed dollar amounts against percentage discounts is usually a waste of your time and traffic.
We already know how customer incentives work at scale. Percentage discounts encourage larger basket sizes, drive higher order values, and generate more total gross revenue for your store.
Stick to the fundamentals. Give new subscribers a clear percentage discount, build clean automations behind it, and let customers spend as much as they want.
Final Thoughts
Optimising your sign-up forms is about maximising downstream revenue, not just email submissions. Percentage-based discounts consistently deliver higher average order values because they reward customers for building larger carts. Set your margin expectations properly from the start and let the math work in your favour.
Build high-converting forms for your store
If you want to turn more website visitors into high-value buyers with proven capture strategies, take a look at our sign-up form services to see how we can help.
