How to split group expenses systematically

Separate shared from personal costs

Shared costs like rent and internet are split by headcount or an agreed ratio.

Personal costs, like an item bought for one person, should be charged only to them, not pooled.

Use the net-balance principle

Instead of recalling who paid what, compute each person's net balance: paid minus should-pay.

Positive means they should be reimbursed; negative means they owe more. This keeps settling simple and transparent.

Set a settlement cycle

• Roommates: settle monthly with the utility bills.
• Friend groups: settle after each trip or event.
• Teams: settle on the company reimbursement cycle.

Example: 3 roommates

Rent 9,000 + internet 600 + utilities 1,200 = 10,800 ÷ 3 = 3,600 each.

This month A paid the full 9,000 rent, B paid 600 internet, C paid 1,200 utilities.

Net: A overpaid 5,400, B owes 3,000, C owes 2,400 → B sends A 3,000, C sends A 2,400. Done.

When someone stays only part of the month

Do not automatically divide every bill by three. First agree whether fixed costs such as rent or internet remain each person's responsibility for the whole month. The group may choose to allocate utilities by days present.

For a 900 THB electricity bill over 30 days, suppose A and B stayed 30 days each and C stayed 10 days. There are 70 person-days. A and B each owe about 385.71 THB, and C about 128.57 THB. Adjust the rounding so the shares still total 900 THB.

Days present are a group convention, not a measurement of actual electricity use. Use separate meter readings or another agreed method if consumption differs substantially.