The setup
Four friends at a bar for three hours. The tab is open under Sam's card. During the night:
- Round 1: everyone gets their own drink (four different drinks).
- Round 2: Rae buys a round of four shots for the table.
- Round 3: everyone gets their own drink again.
- Round 4: only three people are still there; each gets their own drink. Alex has already left.
- Sam orders one solo drink at the end.
The tab itemized
- Round 1: Alex $12, Rae $14, Casey $10, Sam $12 → $48
- Round 2 (shots for the table): 4 × $7 = $28, bought by Rae
- Round 3: Alex $12, Rae $14, Casey $10, Sam $12 → $48
- Round 4 (Alex left): Rae $14, Casey $10, Sam $12 → $36
- Sam's last drink: $12
Subtotal: $172.
Tax and tip
- Sales tax at 8%: $13.76
- Tip at 20%: $34.40
Final: $220.16.
Everyone's share of the subtotal
Attributing each drink to the person who consumed it, and splitting the round-of-shots four ways since all four were there and drank one:
- Alex: $12 (R1) + $7 (shot) + $12 (R3) = $31
- Rae: $14 (R1) + $7 (shot) + $14 (R3) + $14 (R4) = $49
- Casey: $10 (R1) + $7 (shot) + $10 (R3) + $10 (R4) = $37
- Sam: $12 (R1) + $7 (shot) + $12 (R3) + $12 (R4) + $12 (last) = $55
Total: $172. ✓
Proportional split of extras
Extras: $48.16. Each person's share = (their subtotal / 172) × $48.16.
- Alex: $31 + $8.68 = $39.68
- Rae: $49 + $13.72 = $62.72
- Casey: $37 + $10.36 = $47.36
- Sam: $55 + $15.40 = $70.40
Sum: $220.16. ✓
Reimbursing Rae for the shots
Rae bought the round of shots ($28), but the cost was split across all four people in the numbers above. That means Rae already got compensated for the shots in her per-person total — no separate reimbursement needed.
If instead Rae had wanted to gift the round to the table, she would absorb the $28 herself: her per-person total goes up by $28 × ($21/$28) = $21 (the three shares that would have gone to Alex, Casey, Sam), and each of the others' totals goes down by $7 plus their proportional share of tax and tip on that $7.
What made this work
- Sam kept the tab open (one card, one receipt).
- Alex leaving early didn't complicate the math — she just paid for what she actually had.
- The shot round was treated as "shared item split among people who had one" — the fairest default for shared drinks.
For a running bar tab where people come and go, BillSplitterApp lets each person claim only the drinks they had — and handles the tax and tip proportionally without any per-round math.