Group Expense Splitter & Debt Simplifier
A completely free, privacy-first, zero-login alternative to Splitwise. Add your travel group or roommates, log shared expenses, and let our graph-theoretic cash flow algorithm compute the absolute fewest payments needed to settle all debts.
1. Group Members
2. Log Shared Expense
Simplified Settlement Plan
The greedy min-cash-flow algorithm cancels transitive obligations, ensuring the group settles completely in the fewest possible transactions.
Individual Net Balance Waterfall
Green bars denote creditors (members who paid more than their share and are owed money). Red bars denote debtors (members who must transfer funds to square up).
Recorded Expenses History
| Description | Paid By | Amount | Split Among | Action |
|---|
The Min-Cash-Flow Greedy Algorithm
In an unoptimized group of $N$ people, if everyone settles directly with whoever paid for each meal or Uber, there can be up to $\frac{N(N-1)}{2}$ separate transactions. Our engine transforms the ledger into a directed flow network and executes a greedy settlement reduction:
\text{Net}_i = \sum \text{Paid By}(i) - \sum \text{Fair Share of}(i)
2. Partition into Debtors and Creditors:
\mathcal{D} = \{ i \mid \text{Net}_i < 0 \}, \quad \mathcal{C} = \{ j \mid \text{Net}_j > 0 \}
3. Greedy Matching Iteration:
d = \arg\max_{i \in \mathcal{D}} |\text{Net}_i|, \quad c = \arg\max_{j \in \mathcal{C}} \text{Net}_j
m = \min(|\text{Net}_d|, \text{Net}_c)
\text{Transfer: } d \xrightarrow{m} c
\text{Net}_d \leftarrow \text{Net}_d + m, \quad \text{Net}_c \leftarrow \text{Net}_c - m
4. Complexity: Reduces at most $\mathcal{O}(N^2)$ messy payments down to exactly $\mathcal{O}(N-1)$ clean transfers.
5 Critical Group Expense & Roommate Pitfalls
1. Unequal Housing Utility in Group Vacation Rentals
Splitting an Airbnb strictly per capita creates resentment when one couple gets the master bedroom with private en-suite ocean views while another guest sleeps on a pullout sofa. Fair splits should weight square footage, private bathrooms, and bed quality.
2. Foreign Exchange Rate & Credit Surcharge Drifts
On international trips, splitting in local currency (e.g. € or ¥) but reimbursing weeks later in USD causes friction due to FX shifts and 3% foreign transaction fees charged to the primary payer's credit card. Always calculate using the actual converted debit on the payer's bank statement.
3. The Alcohol & Auto-Gratuity Tax Drag
In restaurant group dinners, non-drinkers frequently subsidize high-margin cocktails. Furthermore, large parties trigger mandatory 18-20% auto-gratuity and local sales tax, turning a $30 entree into a $42 liability. Itemizing drinks separately prevents social conflict.
4. The "I'll Buy the Next Round" Psychological Bias
Informal reciprocity fails because human memory exhibits loss aversion: people remember drinks they bought for others far more vividly than drinks others bought for them. An objective digital ledger eliminates reciprocal scorekeeping anxiety entirely.
5. Settlement Drift & Venmo Stalling
Debts not settled within 48 hours of a trip ending experience exponential decay in repayment probability. Generating and sending a definitive settlement plan immediately upon departure prevents uncomfortable reminders weeks down the line.
Graph Theory, Conservation of Flow & Min-Cash-Flow Optimization Mathematics
Naive debt settlement across N participants requires up to N(N-1)/2 individual transactions. Our settlement engine applies a greedy minimum cash flow reduction on directed debt graphs to cap settlement transfers at at most N - 1: