Every progress bar in a basket makes a promise about distance. Get the distance wrong and you are telling a customer the finish line is miles away at the exact moment they can see it.
A homeware retailer I work with ran into this today. The offer was simple. Spend £100, get free delivery and a free gift. Two rewards, one number.
Then a screenshot of the checkout arrived. A shopper at £70 was looking at a bar barely a sixth full. Seventy per cent of the way there, and the bar was telling them they had hardly left the car park.
Nobody had typed a wrong number. That was the trap.
Here is what was actually going on. The basket app spaces its reward markers evenly along the bar, whatever the money says. Two rewards put the first marker a quarter of the way along. With both set at £100, the bar crawled towards that first marker at quarter speed, about 17% full at £70, then leapt to full the moment the hundredth pound landed. Right at £0. Right at £100. Wrong everywhere a shopper actually makes up their mind.
The fix was to give the checkout one real reward, so the bar now moves with the money. £50 shows half full, as it should. The basket still shows both markers, with the second one drawn in by the shop’s own code.
Same day, same offer, the other end of the bar. Once unlocked, the celebration panel on a phone stood 373 pixels tall, a victory parade parked in front of the checkout button. It is now 135. Two ticks say it. The sentence announcing it went.
A progress bar is not decoration. It is a road sign, and a sign that says 80 miles when you are 30 away does not make anyone drive faster. It makes them turn round.