Ask for a record before the guest leaves
Take thirty seconds while the meal is still easy to remember. Write the guest’s meal, their share of common dishes, and whether they already handed somebody cash. A guest who drank tap water may not have agreed to share a round of drinks bought after they left.
Give the guest an estimate they can check
Show the $14 meal and $3 starter share. If the guest leaves $20, mark “received $20; final amount pending” beside their name. That wording lets the group handle the final receipt without treating the extra $3 as a tip or as a promise to cover more food.
Close the bill privately
If someone pays an estimate on the way out, write down the amount received. When the bill arrives, compare it with their final share and send the difference privately. This is easier than asking the entire group to remember their order afterward.
Suppose the guest’s agreed share of the final additions is $2. Their total is $19, so return $1. If they prefer to leave the extra dollar as a tip, confirm that choice. When the group divides the remainder, first deduct the guest’s final share from the actual total, not the amount of cash they happened to leave.