How to Use Seisan-kun
4 simple steps to calculate fair bill splits accurately
4つのステップ
Step 1: Create a Group
Start by creating a group with a name that helps you remember it later. Use names like the event name or member names. You can also choose the settlement currency (e.g. JPY, USD) here — handy for splitting bills on trips abroad.
Step 2: Add Members
Add the people who will participate in the bill split. Only members added to the group will be included in the settlement.
Step 3: Record Payments
When someone pays, record the payment details. Enter who paid, what for, and how much. Also specify who benefited from the payment. You can apply weighted calculations here.
Step 4: Confirm & Execute Settlement
The app automatically calculates who owes whom and how much. Review the settlement details and you're done! Everyone just needs to send their payments.
About Weighted Calculation (Keisha)
Seisan-kun's standout feature is its support for weighted calculations. Unlike standard bill splitting where everyone pays the same, weighted calculations automatically adjust amounts for situations like:
Weighted Calculation Examples
- Drinking or not: Non-drinkers pay less, drinkers pay more
- Duration of stay: Late arrivals pay less, those who stayed the whole time pay more
- Food consumed: Those who ate more pay more, less pay less
- Custom cases: Organizers covering planning costs, or other custom weightings
How Weighted Calculations Work
When recording a payment, you can set a coefficient for each member (e.g., 1x, 0.5x, 1.5x). The app automatically calculates the amount each person should pay based on these coefficients—no complex math needed.
For example, if 5 people go out and someone pays 5,000 yen total:
- Standard split: 1,000 yen per person
- Weighted split (non-drinker at 0.5x): Drinkers 1,200 yen, Non-drinker 800 yen
This achieves a truly fair bill split where nobody loses out.
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