Almost everyone has held a stamp card with just two empty boxes left and gone back in for exactly that reason. Not because that day’s coffee was essential, but because the card was almost full. That pull is not an accident, and it is not a lack of willpower. It has a name, and it has been studied in real detail. Understanding why stamp cards work also makes you better at designing one.
The café study that explains it all
The most important source on this isn’t marketing, it’s research. In 2006, Ran Kivetz, Oleg Urminsky, and Yuhuang Zheng published a study in the Journal of Marketing Research that, among other things, tracked real café customers over several months. The guests had a classic collector card: buy ten coffees, and the eleventh is on the house.
The result was clear, and it’s the whole reason this article exists. People did not buy their coffee at an even pace. The closer they got to the free reward, the shorter the gaps between visits became. In the final stretch before the goal, they visibly sped up. The card itself had changed their buying behavior.
The goal-gradient effect: closer to the reward, faster back
Researchers call this acceleration the goal-gradient effect. The idea itself is old. In early experiments, even rats ran faster the closer they got to the food. But Kivetz and his colleagues were the first to demonstrate it cleanly in real human purchase decisions.
For you at the counter, that has a very practical meaning: a stamp card earns its value not at the start, but right before the end. A guest with a single stamp barely thinks about you. A guest with eight out of ten stamps has a goal within reach, and a reachable goal pulls people back. That’s exactly why it matters so much that guests can see their progress at any time. A card sitting forgotten in a drawer, with nobody sure of the count, can’t create that pull.
The effect also explains the most common, self-inflicted disappointment with loyalty programs: a goal set too far away. Asking for twelve stamps on something a guest buys twice a month means the acceleration never kicks in. They’re stuck in the slow first third forever. We work through how to find the right goal for your business in “How many stamps should your card have?”.
The starter stamp: gifted progress pulls people in
Perhaps the most surprising part of the study isn’t about the end of the card, but its beginning. Kivetz and his colleagues compared two groups:
- One group got a card with ten empty boxes: zero done, ten to go.
- The other group got a card with twelve boxes, two of which were already stamped, meaning ten real purchases to the reward either way.
The effort was identical: both groups had to buy ten times. And yet the people with two gifted stamps completed and redeemed their cards more often, and faster. The technical term for this is endowed progress, progress handed to you as a gift. What decides isn’t the real distance covered, but the feeling of having already set off. Someone starting at “2 of 12” has mentally already stepped inside the program. Someone starting at “0 of 10” is still standing at the door.
That’s the subtle but decisive difference from the goal-gradient effect. One describes how the pull grows near the end; the other describes how you get people moving in the first place. Both point the same way: a visible path that already feels underway motivates more than a blank slate ever could.
What this means for your card
A single well-designed study gives you three very concrete decisions to make. More of the fundamentals live in the guide to loyalty programs.
1. Make progress visible. The pull only forms if guests actually know how far along they are. On paper, that means a card people carry with them and look at. Digitally, the card lives in the phone anyway and updates itself after every visit. Progress sits right there on the lock screen, with nobody having to go looking for it.
2. Give away the first stamp. Instead of “0 of 10,” start guests at “1 of 11” or “2 of 12.” The real effort stays exactly the same, but the feeling changes: they’re already in. The best moment for this is the very first scan. Whoever sets up their card gets the starter stamp on the spot, and never walks away with a blank one.
3. Keep the goal reachable. The goal-gradient effect only works if the end is in sight. Do the math on how often your guests actually come back: daily coffee with ten stamps is two weeks, perfect. A haircut every six weeks with ten stamps would take over a year, too far. Adjust the stamp count until the goal sits in weeks, not months.
Honesty still matters most here. A starter stamp is a friendly nudge, not a trick. The reward has to be real and the path has to be fair. People notice very quickly when a goal has been artificially stretched out, and at that point, the effect flips into its opposite.
Frequently asked questions
What exactly did the Kivetz study measure?
In 2006, Kivetz, Urminsky, and Zheng analyzed, among other things, real collector cards at a café (buy ten coffees, get the eleventh free). They observed that guests sped up their purchases the closer they got to the reward, with the gaps between visits getting shorter. In a second comparison, they showed that people who started with gifted stamps completed the card more often and faster, even though the real effort stayed exactly the same.
What’s the difference between goal-gradient and endowed progress?
The goal-gradient effect describes how motivation grows the closer the goal gets: the pull is strongest near the end. Endowed progress, the “gifted head start,” describes the beginning. People who feel they’ve already covered some ground (say, 2 of 12 instead of 0 of 10) are more likely to stick with it. One works at the end of the card, the other at the start. Both point toward a card with visible progress and a small head start.
Does the effect still work on a digital card?
The study is from the paper era, but the mechanism runs on visible progress, not on the material. A digital stamp card in Apple Wallet or Google Wallet actually has an edge here: it can’t get lost, it’s practically always on hand, and the current count appears automatically on the lock screen after every stamp. With Treuly, the starter stamp can be added right at the first scan. The gifted progress from the study becomes part of the flow, not extra work.