Bill split calculator: how to calculate who owes what
By the Tab Tender team · 5 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.
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.
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.