Bill Splitter

Bill Splitter & Tip Calculator

Split any shared expense fairly. Handles tips, unequal splits, and multi-person debt settlement.

Core Capabilities

• Restaurant bill splitting with tip
• Unequal splits (by percentage, ratio, or custom amount)
• Group trip / multi-expense settlement
• Debt simplification (minimize number of transactions)
• Multi-currency rounding

Formulas

Tip Calculation

tip_amount     = bill_subtotal × tip_rate
total_bill     = bill_subtotal + tip_amount
per_person     = total_bill / num_people

# Suggested tip rates
10% = minimal / poor service
15% = standard
18% = good service (US default)
20% = great service
25% = exceptional

Equal Split

each_owes = (subtotal + tip) / n_people

Unequal Split by Item

person_share = sum(person_items) / subtotal × (subtotal + tip)

Debt Simplification Algorithm

Given a list of balances (positive = owed to person, negative = person owes):

1. Sort by balance descending
2. Match largest creditor with largest debtor
3. Transfer min(|creditor|, |debtor|) amount
4. Repeat until all balances zero
→ Result: minimum number of transactions

Usage Examples

Basic Restaurant Split

Input:
  Subtotal: $120
  Tip: 18%
  People: 4 (equal split)

Output:
  Tip: $21.60
  Total: $141.60
  Each pays: $35.40

Unequal Split by Items

Input:
  Alice ordered: $45
  Bob ordered: $30
  Carol ordered: $25
  Tip: 20%
  Tax: 8.5%

Output:
  Subtotal: $100
  Tax: $8.50
  Tip: $20.00
  Total: $128.50
  Alice pays: $57.83 (45% of total)
  Bob pays: $38.55 (30%)
  Carol pays: $32.12 (25%)

Group Trip Settlement

Input:
  Alice paid hotel: $300
  Bob paid dinner: $120
  Carol paid transport: $60
  3 people, equal share

Output:
  Total: $480
  Each owes: $160

  Balances:
    Alice: +$140 (paid $300, owes $160)
    Bob:   -$40  (paid $120, owes $160)
    Carol: -$100 (paid $60, owes $160)

  Settlements (simplified):
    Carol → Alice: $100
    Bob   → Alice: $40

Interaction Patterns

When user provides a bill, always:

1. Confirm subtotal, tip preference, and number of people
2. Ask if split is equal or by item
3. Show breakdown: subtotal / tip / tax / total / per-person
4. For group settlements: show balance sheet + simplified payment instructions
5. Round to 2 decimal places; handle rounding remainder (assign to first person or largest share)

Clarifying Questions to Ask

• "Is this an equal split or by what each person ordered?"
• "What tip percentage? (15% / 18% / 20% / custom)"
• "Is tax already included in the total, or should I add it?"
• "Do you want me to minimize the number of transactions?"

Edge Cases

Output Format

Always present results in a clear table:

BILL SUMMARY
------------
Subtotal:        $XX.XX
Tip (18%):       $XX.XX
Tax (if any):    $XX.XX
TOTAL:           $XX.XX

EACH PERSON PAYS
----------------
Alice:   $XX.XX
Bob:     $XX.XX
Carol:   $XX.XX

PAYMENT INSTRUCTIONS
--------------------
Bob pays Alice:   $XX.XX
Carol pays Alice: $XX.XX