Flatmate rent splitter: fair to the cent

Four ways to split, and when each is fair

• Equally. Everyone pays the same. Simple, and fair when the rooms are similar and everyone is home about the same amount.
• By room size. Enter each bedroom's floor area (or any relative number, such as 3 for a big room and 2 for a small one). Rent is shared in proportion. Useful when one person has the master bedroom with an ensuite.
• By income. Each person pays the same share of their income. Some couples and close friends prefer this; it needs everyone to be comfortable sharing what they earn.
• By days present. For someone moving in or out partway through, or away for a few weeks. Enter the days each person lived there during the period and both rent and bills are weighted by days.

Bills such as power and internet are often shared equally even when rent isn't, because everyone uses them about the same. Leave "split bills equally" ticked for that, or untick it to split bills the same way as the rent.

Worked example

An invented three-bedroom flat pays $2,160.00 rent a month, plus $286.50 for power and $89.99 for internet. Aroha's room is 14 square metres; Ben's and Mere's are 10 each. Split by room size with bills shared equally:

• Aroha: $889.41 rent + $125.50 bills = $1,014.91
• Ben: $635.30 rent + $125.50 bills = $760.80
• Mere: $635.29 rent + $125.49 bills = $760.78

The three totals add up to $2,536.49, exactly the rent plus the bills. Splitting $1,000.00 three ways equally gives $333.34, $333.33, $333.33: someone has to take the extra cent, and the calculator gives it to the first person in the list, so the shares never fall short of the bill. If Mere had moved in with only 10 days of a 28-day period left, splitting the power bill by days present would give Aroha $121.55, Ben $121.54, Mere $43.41.

Common mistakes

• Mixing periods. Rent is often weekly while power is monthly. Convert everything to the same period first, or the split will be wrong. A monthly bill is roughly 12 ÷ 52 of that amount per week.
• Rounding each share up. If everyone rounds up to the nearest dollar, the flat overpays; round down and the account goes short. Keeping the cents avoids both.
• Forgetting shared spaces. Weighting by bedroom size only shares out the bedrooms. Kitchens, lounges and bathrooms are used by everyone, so some flats split part of the rent equally and only the rest by room. You can do that by running the calculator twice.
• Not agreeing first. The fairest method is the one everyone agreed to before the first bill arrived.

Limits and privacy

This is a calculator, not tenancy advice. It doesn't cover bonds, who is named on the tenancy agreement or what happens when someone leaves; for those questions, start with the government's Tenancy Services website, tenancy.govt.nz. Names, incomes and amounts stay in your browser and are never sent or saved. Only the split method is kept in the page address after the # sign. To add GST to a shared invoice, use the GST calculator.

Last reviewed: 2 October 2026