Bill split calculator: how to calculate who owes what
By Mitch R, Tab Tender Team · 3 min read · Updated June 7, 2026
To calculate who owes what: add up each person's items to get their subtotal, then add their proportional share of tax and tip (their items ÷ the bill's subtotal × the total tax and tip). The sum of everyone's totals equals the bill. A bill-split calculator does this for you from the receipt.
Working out exactly who owes what on a shared bill is a small, annoying math problem: it's not just dividing by the number of people, because tax and tip have to be shared fairly too. Here's the simple formula, a fully worked example you can copy, and the fastest way to skip the arithmetic entirely.
On this page
The formula
Each person's fair total has two parts: the items they ordered, plus their proportional share of the tax and tip. The proportion is just their items divided by the bill's subtotal.
- Person's subtotal = the sum of the items they ordered.
- Their share of tax + tip = (their subtotal ÷ bill subtotal) × (total tax + tip).
- Their total owed = their subtotal + their share of tax + tip.
- Check: everyone's totals should add up to the final bill, to the cent.
A worked example
Say three friends have a $90 subtotal, with $7.20 tax and $18 tip ($25.20 in shared charges). Alice ordered $40, Ben $30, and Cara $20. Each person's share of the $25.20 is their slice of the subtotal:
| Person | Items | Share of tax+tip | Total owed |
|---|---|---|---|
| Alice | $40.00 | 44.4% → $11.20 | $51.20 |
| Ben | $30.00 | 33.3% → $8.40 | $38.40 |
| Cara | $20.00 | 22.2% → $5.60 | $25.60 |
| Total | $90.00 | $25.20 | $115.20 |
The mistakes people make
- Splitting tax and tip evenly instead of proportionally — it overcharges whoever ordered least.
- Tipping on the post-tax total by accident, or tipping again on top of an automatic gratuity.
- Rounding each share independently so the parts no longer add up to the real bill.
- Forgetting shared items (an appetizer) belong only to the people who actually had them.
How do you handle a discount or a coupon?
A whole-bill discount — a coupon, a happy-hour deal — comes off the same way tax and tip go on: proportionally to each person's share of the subtotal, so everyone's total drops by the same percentage. A discount tied to one item (a comped entrée) simply comes off that one person's subtotal before you work out anyone's share.
What if someone paid part of the bill in cash?
Treat a cash contribution as a prepayment: calculate everyone's fair total the normal way first, then subtract what that person already put in from what they owe. If they overpaid, the difference is money the group owes them back. The order matters — work out the fair shares first and apply the cash second, so the proportions stay correct.
Or skip the math with a free calculator
You don't have to run these percentages by hand. Tab Tender is a free bill-split calculator that does it from the receipt: snap a photo (or paste a digital one), tap who had each item, and it computes everyone's exact total — tax and tip spread proportionally, parts reconciled to the cent. Then it hands each person a pay link for their share via Venmo, Cash App, or Zelle, so calculating who owes what and actually collecting it happen in one step.