Strip the label away and the two structures have little in common. A single family office (SFO) is a private operation one family owns, staffs and funds to look after its own wealth. A multi-family office (MFO) is a commercial firm that does comparable work for several unconnected families and charges them fees for it. One is a household institution; the other is a business with clients, a price list and a growth plan.
The Carry's test for telling them apart is simple: ask who the office answers to. The distinction matters well beyond the wealth-management trade press. A family office joins a UK startup round somewhere every week, and which kind it is changes who you are actually dealing with, how fast decisions arrive and what the money is likely to do next. Here is how the two differ on who they serve, who pays, and how each behaves on a cap table.
One structure spends its own money. The other is paid to look after someone else's.
What is a single family office?
A single family office is a private company or team that one family owns and funds to manage its own wealth, with no outside clients. The work usually runs past investing into everything that surrounds serious money: tax administration, property, philanthropy, succession.
The defining economic fact is that an SFO is a cost centre. Salaries, systems, office space, legal and compliance support all come out of the family's pocket, in good years and bad. Nothing is sold, so nothing offsets the bill. That is also the source of its appeal. The office answers to one family and nobody else, runs whatever mandate the principals set, and keeps the family's affairs entirely in-house.
In practice the term stretches from two trusted staff and an accountant to a fully built investment operation running direct deals. The label describes ownership, not size.
What does a multi-family office do?
A multi-family office manages investments and administration for several unconnected families at once, as a business. Clients typically pay a management fee calculated on assets, plus charges for services such as reporting, tax coordination or estate work, and in return they share an infrastructure none of them has to build alone.
Some MFOs began life as one family's SFO and opened the doors to others to spread the cost; others grew out of private banks and wealth managers moving up the scale. Either way, the client is buying coverage: an investment team, custody and reporting plumbing, and a bench of specialists that would be hard to justify for a single balance sheet.
Serving unconnected families commercially is also where regulation starts to bite. UK financial services law contains no definition of, and no exemption for, a family office, as Chambers and Partners sets out, and the question of when an office needs FCA authorisation has its own page: does a family office need FCA authorisation in the UK.
How big does a family office need to be?
There is no threshold. No statute, regulator or industry body sets a minimum size at which a family office becomes legitimate, and the round numbers quoted online are conventions rather than rules.
What actually decides it is arithmetic. A dedicated SFO carries a full fixed cost base, so in practice it tends to appear where family wealth reaches nine figures and the running costs stop being the story. An MFO's entry points sit materially lower, because the same costs are spread across its client list. That is the structure's whole reason to exist.
The published research skews large. The UBS Global Family Office Report series, the best-known survey of the sector, draws on offices whose assets average in the billions of dollars, which says more about who answers surveys than about where any entry line sits. Nor is the single-family form fading at the top: roughly two-thirds of the new family offices tracked in 2025 were single-family, per industry reporting.
How does each show up on a UK startup cap table?
Differently enough that hearing 'a family office is joining the round' tells you very little on its own. An SFO in a round is one family's own capital, deployed by someone answering directly to the principal; an MFO is usually a professional allocator putting client money to work under a mandate.
That difference shows up in behaviour. An SFO can move fast on conviction, take an odd-shaped deal because the principal likes it, and hold through a downturn without a committee to persuade. The flip side is that follow-on money depends on one family's appetite and one family's liquidity. An MFO brings process: investment committees, allocation rules, diligence checklists. Slower, but more predictable, and likelier to arrive through funds, structured co-investments or pooled vehicles than through a one-off cheque. The mechanics of those club deals are covered in how family offices co-invest with angels and VCs, and the full map of the routes, from direct deals to funds and SPVs, in how do family offices invest in UK startups.
UK tax adds one wrinkle worth a sentence. SEIS and EIS income tax relief (50% on up to £200,000 a year, 30% on up to £1m, or £2m where at least £1m goes to knowledge-intensive companies, per GOV.UK) belongs to individual investors only, with three-year minimum holds. Family members subscribing personally can claim it; the office as an entity cannot, whichever structure it is. The full eligibility picture is in can a family office claim SEIS or EIS tax relief.
How does a family choose between an SFO and an MFO?
As a build-or-buy decision, weighed factor by factor, and it is rarely permanent: plenty of families keep a small SFO for control and privacy while renting an MFO's infrastructure for the rest. The factors that actually move it:
- Cost against scale. A fixed cost base only earns its keep above a certain size; a fee schedule scales down as well as up. The crossover is arithmetic, and every family's arithmetic is different.
- Control and tailoring. An SFO does exactly what one family wants, at the family's pace. An MFO tailors within a framework built for many.
- Privacy. An SFO keeps everything in-house. An MFO is a firm, with staff turnover and other clients down the corridor.
- Talent. Hiring and keeping an investment team for a single family is hard; an MFO spreads its bench across the client list.
- The startup question. A live direct programme needs sourcing, diligence hours and reserves for follow-ons. Families with that machinery lean towards an SFO or a hybrid; families without it tend to reach startups through an MFO's funds and co-investments.
What none of this is: a recommendation of either structure, or of any provider. This page is general information, not financial, tax or legal advice. Structure interacts with the family's tax position and, at the edges, with the FCA perimeter, so confirm the current scheme rules on GOV.UK, take FCA-regulated advice on the decisions themselves, and, where regulated activity is in question, regulated legal advice too.
Frequently asked questions
What is the difference between a single family office and a multi-family office?
A single family office is a private structure one family owns and funds to manage its own wealth; it has no outside clients. A multi-family office is a commercial firm doing similar work for several unconnected families, which pay fees for it. The practical differences follow from that: an SFO is a cost centre offering total control and privacy, while an MFO offers shared infrastructure at a lower entry point.
What does a multi-family office actually do?
It manages investments and the administration around them for its client families: portfolio management, reporting, custody arrangements, and often tax coordination, estate work and similar services. Clients typically pay a fee based on assets plus charges for specific services. The appeal is access to an institutional-grade team without having to fund one alone.
How much money do you need to set up a family office?
There is no legal or regulatory minimum. The real constraint is cost: a dedicated single family office carries full staffing and infrastructure costs, which is why in practice they tend to appear where family wealth reaches nine figures. Multi-family offices exist precisely to lower that entry point by sharing costs across several client families.
Is a multi-family office regulated in the UK?
There is no family-office category in UK financial services regulation, so it depends on the activities. A firm managing or advising on investments for several unconnected families on a commercial basis is far more likely to be carrying on regulated activities, and so to need FCA authorisation, than a family running its own money. The position is fact-specific, and regulated legal advice is the way to settle it for any particular office.
Is a single family office better than a multi-family office?
Neither is better in the abstract; they solve different problems. An SFO maximises control, privacy and tailoring at a fixed cost that only large fortunes absorb comfortably. An MFO trades some of each for shared costs and an existing team. Which fits depends on scale, on the family's appetite for building an operation, and on what it wants the office to do. This is general information, not financial advice; an FCA-regulated adviser can weigh a specific situation.