11 people. $650 bill. Birthday girl pays $0.

The scenario

Twelve people at a steakhouse for Sarah's birthday. The understanding is clear: Sarah doesn't pay. She orders the lobster ($65) because, well, it's her birthday.

The bill arrives: $650 including tax and tip. Eleven people need to cover it, including Sarah's lobster. But here's where it gets messy: Mike ordered a $75 porterhouse. Jessica had a $22 chicken dish. Should they contribute the same amount toward Sarah's share?

Split evenly, everyone pays $59. But Jessica, who ordered $22 worth of food, is now paying nearly triple her actual consumption. Meanwhile, Mike's $75 steak is effectively discounted by Jessica's contribution.

The solution

splitty handles birthday dinners elegantly. Scan the receipt. Assign items to everyone except Sarah. Her share—the $65 lobster plus proportional tax and tip—gets distributed among the 11 paying guests based on what they ordered.

Mike, with his $75 steak, contributes more toward Sarah's share. Jessica, with her $22 chicken, contributes less. Fair to Sarah (she pays nothing). Fair to everyone else (contribution matches consumption).