You'll have seen it a hundred times - you're about to check out, and a cheerful little message tells you you're a few quid short of free delivery. So you go back and find something else to add, and somehow end up spending more than the postage would ever have cost you.
It's one of the oldest tricks in online retail, and it works because paying for delivery feels like a penalty in a way that spending the same amount on an actual product somehow doesn't.
We rolled one of these out recently on an e-commerce shop we look after - the "spend a bit more to get free shipping" box - and we've now got enough data to take an early look at whether it earned its place.
The short version is that it's looking promising. The longer version has a few more caveats, which we'll get to, because we'd rather tell you the truth than a tidy story.
The short version
Comparing the period before the box went in with the period since, the share of orders qualifying for free shipping climbed from 75.8% to 83.7%. That's a rise of nearly eight percentage points, or a touch over 10% in relative terms - which indicates more people nudging their baskets over the line to avoid the delivery charge.
Average order value, stripping out the shipping itself, went from £34.70 to £37.43, so an 8% lift. People aren't just qualifying for free delivery more often, they're spending more to get there, which is rather the point.
And orders per day went from 2.1 to 3.4 - up a hefty 62%.
On the face of it, that's three numbers all pointing the right way, which is exactly what you want to see.
The longer version
A proper statistician would take one look at this and grumble that there's nowhere near enough data to call any of it statistically significant, and they'd be right. These are early figures from a modest number of orders, not a verdict carved in stone.
The orders-per-day jump is the one to be most wary of. We're heading into the back end of the year, with Christmas on the horizon - and there have been ad campaigns running over the same stretch. Both of those push order volume up regardless of anything we did at the checkout, so pinning that 62% on the free-shipping box alone would be wishful thinking.
The two figures we trust more are the free-shipping percentage and the average order value, because those speak to how people behave once they're already in the basket, which is precisely what the box is designed to influence. Christmas approaching brings you more shoppers, but it doesn't obviously explain why a larger slice of them are topping up to clear the free-delivery threshold. That pattern looks a lot more like the nudge doing its job.
What to take from it
Two things, really. The first is that a free-shipping threshold is a cheap, low-risk change that's very likely earning its keep here, and the early signs are encouraging enough that we'll happily let it run and keep watching.
The second is the more important one, and it's a drum we bang a lot - none of this means anything unless you're measuring it.
If we hadn't had clean before-and-after figures, the box would just be a nice idea somebody had, and we'd be guessing. Because we tracked it, we can see what moved, be honest about what's noise, and make a real decision rather than a hopeful one.
If you're running an online shop and you've never tested something as simple as this, or you're making changes and crossing your fingers rather than watching the numbers, then that's exactly the sort of thing we help with, so let's have a chat.