The Fair Share Standard
High-Signal Summary
Fairness requires precision. HackBill rejects "even splitting." Instead, liability is calculated by summing explicitly claimed items. The tip is then distributed proportionally: if you consumed 20% of the bill's value, you pay 20% of the total tip. If someone opts out, their forfeited tip is split equally among remaining tip-payers.
Why This Matters
The "Even Split" (Total / People) is a social convenience that mathematically penalizes light eaters.
The Subsidy Problem: If User A orders a $50 steak and User B orders a $10 salad, an even split ($30 each) forces User B to subsidize User A by $20. This friction discourages group dining.
The "Zero Math" Advantage
HackBill eliminates the cognitive load of fairness. Users do not need to calculate percentages or tax ratios. They simply tap what they ate. The algorithm instantly computes the exact liability, including proportional tip, in milliseconds.
The Decision Logic
User Claims specific items (e.g., "Burger", "Fries")
Item Share = Sum(Price * Quantity)
Tip Amount > 0
User Tip Share = Total Tip * (User Item Share / Total Bill Subtotal)
Total Liability = Item Share + User Tip Share
Mathematical Proof
| User | Order | Cost | Even Split | Fair Share |
|---|---|---|---|---|
| Alice | Steak | $80.00 | $50.00 | $80.00 |
| Bob | Soda | $20.00 | $50.00 | $20.00 |
*Bob saves $30.00 by using the Fair Share Standard.