How to increase tips without asking for them

Tips are a design problem. A tip jar depends on someone noticing it. A terminal prompt depends on a server handing it over. A checkout screen shows the same three options to every guest, every time.

Put the presets above the total, not below it. Show the dollar amount next to the percentage so nobody does math while their food is going cold.

Keep the options honest. Three presets and a custom field is enough. Guests who feel pushed tip less, not more.

Then look at the data by shift. If one service consistently runs lower, the problem is usually pace, not the screen.