How much does living alone cost compared to sharing?

Per person, more at every step of the curve. On the 2023 survey's comparable categories, a one person household spends about $791.10 a week, while each person in a two person household accounts for about $736.20: a single-person premium of about 7 per cent against a couple, and the gap keeps compounding: each person in a five person household accounts for barely half what one person alone spends. The dwelling, power, insurance and car are household costs, and the fewer people share them, the more each carries.

What does a second person add to a household budget?

About $681 a week on the measured averages, far less than doubling the one person figure, because the second person joins an already-running household. By the fifth person the marginal cost is about $-46 a week. Each additional person costs less than the one before.

Do these figures mean flatting saves money?

Yes, and they measure how much: sharing spreads the household-level costs, which are the majority of any budget, across more people. The same arithmetic is why a couple separating nearly doubles total costs, and why a retiree living alone needs well over half a couple's budget. It is the most powerful budget lever most people never think of as one.

Are bigger households in the data just richer?

They spend more in total and have higher household incomes on average, but the per-person figures fall as size rises regardless. The economies of scale are physical, one roof and one power connection shared, rather than an artefact of who earns what.

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What Household Size Does to a Budget

Household size explains more of the difference between two budgets than income does, and almost every budgeting comparison ignores it. The measured figures, from the 2023 survey, per household and per person:

Household	Weekly total	Per person
1 person	$791.10	$791.10
2 people	$1,472.40	$736.20
3 people	$1,762.60	$587.53
4 people	$2,143.90	$535.98
5 people	$2,097.50	$419.50

Read down the right-hand column and the whole guide is in it: the cost of a person falls every time another person joins the household. One person alone carries about 7 per cent more per head than each half of a couple, and by five people the per-person figure is barely half the solo one. The totals are averages over all households of each size, at 2023 prices, summed across the categories published cleanly for every size (4 suppressed categories excluded from every row).

Why the curve falls: households, not people, spend

Most of a budget is attached to the dwelling rather than the people in it. The rent or mortgage, rates, insurance, the power connection, the broadband, the car in the drive: none of these know how many people live behind the door. Food, clothing and personal spending scale with heads; nearly everything else scales with households. So each additional person shares the fixed base a little further and adds only their per-person costs on top.

The measured marginals make it concrete: the second person adds about $681 a week to a one person household's total, while the fifth adds about $-46 to a four person one. Each person costs less than the person before, and the first person, who buys the whole fixed base alone, is the dearest, with each arrival cheaper than the last.

One caveat belongs here rather than in a footnote: these are averages across all households of each size, and bigger households differ from smaller ones in more than headcount, in age, income and where they live. The curve is real and physical, but the exact dollar gaps carry those differences inside them.

The decisions the curve actually prices

Flatting is the curve used deliberately: three people splitting a household's fixed base each live near the falling end of the per-person column, which is why the flat is the standard answer to a starting salary, priced in the flatting guide and the rent split calculator.

Separation is the curve run backwards, and it is brutal: one household's costs become nearly two households' costs while total income stays the same. The near-doubling, not lawyers, is the main reason separation is financially devastating, and the relationship-ends pathway starts from exactly this arithmetic.

Widowhood in retirement is the gentlest version of the same fact: the survivor keeps most of the couple's fixed base on a reduced income, which is why the retirement spending guide insists a couple's plan be tested at the one person figures.

A new baby, against instinct, moves the total least of the four: an infant adds per-person costs to an existing base. The real financial event of a child is the parental income change, not the household spending change, which the having a baby pathway takes in order.

Test Your Knowledge

Quiz on the size curve

1. What happens to the cost per person as a household grows?

It falls with every additional person, because the fixed household base is shared further

It rises, because bigger households need bigger houses

It stays constant

It falls until three people, then rises

2. Which costs scale with the number of people?

Rent, rates and insurance

Food, clothing and personal spending; the dwelling-attached costs do not

All costs equally

Power and broadband

3. Which life event does the curve price most brutally?

A new baby

Separation: one household's fixed base becomes nearly two, on the same total income

A flatmate moving in

Children leaving home

4. Why does a new baby move household spending less than people expect?

An infant adds per-person costs to an existing household base; the real financial event is the change in parental income

Babies are subsidised into costlessness

The survey does not count children

It moves spending more than any other event

5. What caveat rides with the exact dollar gaps between household sizes?

The figures are medians, not averages

Households of different sizes also differ in age, income and location, and those differences sit inside the gaps

The survey excludes renters

There is no caveat; the gaps are pure size effects

Frequently Asked Questions

How much more does living alone cost per person?

About 7 per cent more than each half of a couple: $791.10 a week against $736.20 per person, on 2023 figures.

What does each extra person add?

Less each time: about $681 a week for the second person, falling to about $-46 for the fifth.

Where is the full split?

Every category by household size is in the household spending section, and the budget calculator benchmarks your lines against your own size.

Related calculators and guides

Budget Calculator, benchmarked to your household size.
Flatmate Rent Split Calculator, the curve used deliberately.
What retirement actually costs, when two becomes one.
What it costs to live in NZ, the totals this guide divides.
What your income decile spends, why size confounds income comparisons.