What it really means
The practice of dividing a restaurant tip proportionally based on what each person ordered, rather than splitting it equally. If you ordered $20 worth of food and your friend ordered $60, you should pay $4 in tip (20% of $20), not $8 (half of the total $16 tip). The difference adds up.
The research: Professor Michael Lynn at Cornell analyzed tipping across group sizes. Solo diners tip an average of 19%. Parties of 4-6? Just 11%. That’s a 42% decline—even though the server did more work. Psychologists call it ‘diffusion of responsibility’: everyone assumes someone else will cover it.
Why it matters: On a $400 bill with 8 people, a 20% tip is $80. Split evenly, that’s $10 per person. But if one person ordered $100 worth of food and another ordered $25, should they really tip the same amount? Fair tip splitting says no.
The math: Your tip = (your order total / group order total) × total tip. If you ordered $30 out of a $200 subtotal and the tip is $40, you owe $6 in tip, not $10.
The hack: Apps like splitty calculate proportional tip automatically. When you assign items to people, the tip distributes based on order size. No calculator required. No arguments about who should tip more.
