A family office is mostly a set of books and the people who act on them: one record of every entity, account and asset a family owns, measured on one set of rules, plus the lawyers, accountants and investment professionals who make decisions from it. Building one means deciding who keeps that record, and who does everything else.
For most of its history the record and the people came as a package, which is why family offices have belonged to fortunes in the hundreds of millions. The record part no longer has to.
What does a family office actually do?
Strip away the mystique and a family office does six jobs:
Consolidated reporting. One balance sheet across every account, property, company and trust, updated as values change.
Performance measurement. What each holding, and the whole family, actually earned on the money invested, net of deposits and withdrawals.
Cash and bills. What comes in, what goes out, how long the cash would last, and whether spending is growing faster than income.
Tax records. Cost basis, realized gains, estimated tax through the year, and a clean pack for the accountant.
Estate records. Who owns what, through which entity, at what percentage, and who should know where everything is.
Coordination. Getting the right numbers to the estate attorney, the CPA and any investment adviser, and acting on their advice.
What does a traditional family office cost?
A lot, which is why few families have one. In UBS’s Global Family Office Report 2025, the 317 single-family offices surveyed served families with an average net worth of $2.7 billion and managed $1.1 billion on average. Their operating costs ran at roughly 0.35% to 0.44% of assets a year. For the smallest group in the survey, offices managing $100 million to $250 million, that’s about 0.42%: around $420,000 a year for every $100 million.
Most of that is people: the staff who keep the books, run the reports, chase the statements and coordinate the advisers. Those salaries don’t shrink in proportion when the fortune does, which is why the model doesn’t scale down to a household with $1 million or $5 million spread across accounts, a home, a rental and a trust.
Which of those jobs are measurement, and which are judgment?
This is the useful line. Look at the six jobs again:
Measurement: consolidated reporting, performance measurement, cash and bills, tax records, estate records. These are records kept on consistent rules. They can be software.
Judgment: what to buy or sell, how to structure ownership, how to reduce tax, how to plan an estate. These belong to licensed professionals, chosen by the family, who are accountable for their advice.
A family office at its best does both, but the judgment is only as good as the record it’s made from. A CPA working from last year’s spreadsheet and six institutions’ statements is guessing at part of the picture. The same CPA working from one current, consolidated record isn’t.
How to set up a trust, form an LLC or structure a holding company is a question for an estate attorney and a CPA, and this essay doesn’t answer it. What follows is the measurement side: once the structures exist, what does the record look like?
What does it look like for a household with a trust and an LLC?
Take a household with:
a joint brokerage account worth $420,000
two 401(k) accounts worth $310,000 together
$60,000 in cash
a home held in a revocable trust, worth $900,000, with a $400,000 mortgage
a 50% interest in an LLC that owns a rental property worth $600,000, with a $350,000 mortgage, $20,000 in the LLC’s bank account, and $5,000 of tenant security deposits it owes back
The common way to add this up nets the home’s mortgage, because it’s the family’s own, but lists the rental at its market value, because it feels like the family’s property. That gives $1,890,000.
The family-office way records each entity on its own books, nets its debts, and counts the household’s share:
Joint brokerage: $420,000
401(k)s: $310,000
Cash: $60,000
Home (trust): $900,000 − $400,000 mortgage = $500,000
LLC: ($600,000 + $20,000 − $350,000 − $5,000) × 50% = $132,500
Household net worth: $1,422,500
The quick sum overstates the household by $467,500, a third. It counts the rental at full value when the household owns half of it, and it ignores the LLC’s mortgage and the deposits it owes back.
The same discipline applies to returns. Say the household put $100,000 into the LLC four years ago, received $6,000 in distributions at the end of each year, and its half is worth $132,500 today. The equity grew from $100,000 to $132,500, which looks like about 7.3% a year. Counting the distributions and when they arrived, the money-weighted return on what the household actually invested is about 12.7% a year. Neither number is wrong; they answer different questions, as essay seven explained. A family office reports the one that says what the money earned.
What does the software do, and what does it not do?
The books of a family office used to need a staff. Software can now keep them for a household:
every account connected read-only, or entered by hand
every trust, LLC and holding company on its own books, with ownership percentages and a consolidated view
returns on the money actually invested, per holding and per entity
cash flow, runway and savings rate
taxes estimated through the year, and a pack for the accountant
a record of beneficiaries and where everything is
read-only access for the family's own CPA, attorney or adviser, granted and revoked by the family
What it does not do is the judgment. It doesn’t recommend investments, choose structures or give tax or legal advice, and it can’t move money. Those decisions stay with the family and the professionals they hire. The family can give its CPA, attorney or adviser read-only access to the same current, consolidated record, and take it back at any time. That’s the sixth job, coordination, without the staff in the middle.
Nothing here is advice. It’s the arithmetic, explained plainly.
If you want the instrument behind the writing: Eudos is the wealth intelligence platform for wealth builders. It keeps every account, property, trust, and entity on its own books, counts each at the household’s ownership share, and measures returns on the capital actually invested. It’s in private beta; the waitlist is at eudos.com.
To see a household kept this way, open the demo, a fictional family’s wealth with no sign-up. The Thompsons have a joint portfolio, an LLC holding a brokerage account, a trust holding a rental, and a family-office entity that ties the LLC and the trust together at their ownership percentages.