Order summary

A checkout asks for a series of commitments, and the summary is the only thing on the screen that says what they are for. It stays put while the form changes underneath it, carrying the items, their quantities, and every line that adds up to the number at the bottom. Persistence is most of the design: a recap that appears only on the last step is a reveal, and the reader has already spent four screens not knowing what they were agreeing to.

Unexpected extra costs are the single most cited reason people abandon a cart, and the research from Baymard Institute has said so for years. That makes shipping the line to be most careful about. If it cannot be known before an address is given, say so in that row rather than leaving it out, and say what decides it. The rule generalises: every cost gets a row with a name, including the ones a seller would rather not itemise, and a row that cannot be filled yet says why instead of hiding.

The honest version is defined by its dishonest twin. Drip pricing reveals fees one screen at a time so the advertised number stays low and the reader has already invested too much effort to leave by the time the total is real, which puts it squarely in the dark pattern family and, in several jurisdictions, on the wrong side of the law. The tell is not that a total changes: totals should change when the reader changes something. The tell is a total that changes because the seller advanced the step. Recalculate visibly, keep the arithmetic where the reader can follow it, and let a discount insert a named row rather than quietly editing the subtotal.

Beside a summary, a discount field is a small trap worth naming: an empty promo box sends people out of the checkout to hunt for a code they do not have. Keep it quiet, keep it inside the panel, and never let it look like the main action. And where check answers is the same idea for a form, this is the version for money: both put everything that was decided on one screen before it is final, but one is reviewed for accuracy and the other is reviewed for cost, which is why every line here carries a number and the last one is the only one people read twice.