What the data actually shows
The classic demonstration is Prelec and Simester's study, memorably titled 'Always Leave Home Without It' (2001). In auctions for tickets, they found people were willing to pay substantially more when told they would pay by credit card than when told they would pay in cash — a sizeable gap for the identical item. The method of payment, not the price or the product, moved how much people would spend.
Later behavioral research built this into a broader idea: the 'pain of paying.' Work in this tradition (associated with researchers such as Zellermayer and Soman) links payment methods that feel less tangible to higher spending and to weaker memory of what was spent. When the act of paying is nearly invisible — a tap, a saved card, an app that charges later — the spending leaves a fainter trace, and fainter traces are easier to repeat.
The general pattern across this literature is consistent in direction even where the size of the effect varies: reducing the friction and salience of payment tends to loosen spending. Tap-to-pay and one-click checkout are the most frictionless methods yet, which is part of why they are so widely adopted by sellers. The exact magnitude depends heavily on the person, the purchase, and the study, so the honest framing is a reliable nudge rather than a fixed percentage.
Why this feels different from how it actually is
Cash makes the cost concrete in a way digital payment does not. You watch a physical thing leave your hand and your wallet get thinner, and that small, slightly uncomfortable moment is exactly the feedback that makes you pause. A card or phone collapses that moment into a beep, so the same purchase simply feels lighter.
It also feels different because the consequence is delayed and abstracted. With cash, the money is gone now. With a card, the reckoning arrives weeks later on a statement that lumps dozens of unrelated purchases together, so no single buy ever feels like much. The brain that approves the purchase and the one that pays the bill barely meet.
And because frictionless payment leaves a weaker memory, you genuinely lose track. People routinely underestimate what they spent over a month when most of it went on cards or apps, not because they are careless but because each transaction barely registered. The convenience that makes digital payment pleasant is the same property that makes it forgettable.
What the research says to do about it
The most direct lever is to re-introduce friction where it helps. Some people use cash or a prepaid amount for the categories they tend to overspend on — eating out, impulse buys — precisely because the act of paying becomes tangible again. The point is not to abandon cards but to put a deliberate speed bump in front of the spending you actually want to slow.
Restoring visibility is the other research-supported move. Because digital spending leaves a faint trace, anything that makes the total visible again — checking a running balance, a simple spending tracker, or a card app that pings you after each purchase — partly rebuilds the feedback that cash provided for free. The pain of paying can be reconstructed on purpose.
Adding a small pause to frictionless flows also helps. Removing saved cards from shopping sites, turning off one-click checkout, or imposing a short waiting period before non-essential purchases reinserts the moment of decision that tap-to-pay erases. None of this requires more discipline in the moment — it works by changing the moment itself.
What the research says does not help
Simply resolving to 'be more careful with the card' tends not to work, because the effect operates below deliberate attention. The whole point of the pain-of-paying research is that the friction does the work; willpower applied at the register is fighting against a system specifically engineered to feel effortless.
Switching everything to cash is rarely the answer either. For many people cash is impractical, and the research does not say cards are bad — it says frictionless payment is easy to under-feel. Blanket avoidance throws away genuine convenience and security to solve a problem that targeted friction handles better.
Chasing rewards and points as a spending strategy can quietly cut the other way. Cashback and points are real, but they only pay off if they do not nudge you to spend more than you would have, and the same low-friction psychology that earns the rewards is what loosens the spending. The data does not say rewards are a trap, only that they do not cancel the underlying effect.
Real numbers in context
Cash is now a small and shrinking share of how people pay. In the United States, cash accounts for only roughly a fifth of payments by number and a much smaller share by value, with the rest on cards and digital methods (Federal Reserve Diary of Consumer Payment Choice). For most people, in other words, the frictionless mode is now the default mode, not the exception.
The size of the spend-more effect is real but should be held loosely. Prelec and Simester (2001) found people would pay markedly more by card than cash for the same item, and the broader pain-of-paying literature points the same way, but the magnitude varies widely by purchase and person. The dependable takeaway is the direction — less tangible payment tends to mean looser spending — not a single headline percentage.