Isolate add-on costs to reduce payment friction

The Pain of Paying and How to Reduce It

Prelec and Loewenstein's research on "pain of paying" established that spending money activates an aversive emotional response - and that different payment framings produce different intensities of this response. Showing a revised total that is conspicuously larger than the previous total makes the incremental spend feel significant. The customer's attention is drawn to the overall number, which now feels higher and more costly.

Isolating the add-on as a separate, small incremental spend ("for just £3") keeps the customer's attention on the add-on cost rather than the revised total. A £3 decision is evaluated differently from a decision that makes a £48 basket become a £51 basket - even though these are the same thing.

The Specific Pattern to Use

On cart pages, post-purchase upsells, and checkout add-on prompts, use this structure:

"Add [item] for just £[small amount]"

Avoid: "Your new total would be £[larger number]"

The word "just" does important work - it signals that the speaker considers the amount trivial, which primes the customer to evaluate it the same way.

Where to Apply It

Cart drawer upsell widgets. Post-add-to-cart modal upsells. Checkout order bumps. Anywhere you are asking the customer to consider an additional cost, frame it as the isolated incremental amount rather than its effect on the total. Let the customer see the total elsewhere - just not in the same cognitive frame as the add-on decision.

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Research: Prelec & Loewenstein (1998), Marketing Science - the red and the black: pain of paying.